Distortions in the form of disagreement between percept and reality.
Study of sensory processes, first contact between the organism and the environment. Focus on less complex aspects of experience.
Interested in conscious experience of objects. How do we form conscious representations?
Meaning how we know the world. Lies between perception and learning and is very broad.
Used to describe the whole process which leads to identification and interpretation of stimuli. Assumed to incluce a sensory (or registration) phase, a perceptual (or interpretation)stage, and a cognitive (or memoric) phase.
Analysis of all stages of information processing.
Based on the notion that for any given aspect of the observer's sensation there is a corresponding physiological event.
Modularity of perception
Views the mind as a set of distinct units or mudules, each of which is complete in itself and has a specific funcition with specific neural hardware.
Believes that all information needed to form a conscious percept is available in the stimuli that reach our receptors.
Are fixed properties of a stimulus.
Acition possibilites which are available to the observer: Picking up an object and using it.
Label for the calculating features of objects or aspects of the environment from aspects of the stimuli reaching the observer.
In addition to the information from our senses we use our previous experiences, our expectations, and so forth.
"State that our final conscious impression may involve combining a number of different factors to ""construct"" the final percept."
First person data
Subjective date by the person who experiences.
Third person data
Objective data. Gathered through carefully experimentation.
The study of the relationship between the physical stimuli in the world and the sensations about them that we experience.
Problem of it: Measure the minimum intensitiy of a stimulus that we can perceive.
How different do stimulu have to be?
Addressed by measuriing sensation intensity.
Invovles being able to attach learned label or category name to the stimulus just encountered.
A threshold that lifts the sensation over the threshold of consciousness.
Describes the relationship between stimulus itensitiy and yes responses of the existence of the stimulus.
Method of constant stimuli
In this the experimenter selects a constant or fixed set of tones to present. The tones differ in their intensity, some heard very easily and others not heard at all. Commenly a S-shaped curve is obtained from this method. Although it can produce useful estimates of absolute threshold, its main drawback is that it is time consuming because each stimulus has to be presented a number of times to get a stable estimate of the likelihood that it will be detected.
Method of limits
In this the experimenter begins by presenting an observer with a stimulus at an intensity high enough to be easily heard and then decreases it s intensity in small steps until the observer reports I no longer hear it. On average, the descending series yield lower thresholds than the ascending series.
Keeps the stimuli hovering around the threshold by adapting the sequence of stimulus presentations to the observer's responses.
Is the simplest example of adaptive testing to find thresholds. Using the observer's previous responses to determine the stimulus series allows the experimenter to zero in on the threshold quickly and efficiently, with few wasted trials and with a high degree of reliability.
Are trials were no stimulus is presented. An honest and accurate observer should always respond no on catch trials. But even honest observers often report that they really hear something like the tone they are trying to detect, even when it is not there!
Signal detection theory
"It acknowledges that any stimulus must be detected against a background of ongoing internal noise in our sensory systems as well as ongoing noise in the environment. In this theory, there is no absolute threshold
Is the level that is above a particular level. Motivation and expectation can determine where the criterion is placed. For example a radiologist may set a criterion value that is quite low, not wanting to miss any danger signals.
In signal detection theory it refers to the average amount of sensory activity a given signal adds to the average amount of sensory activity present in the absence of the signal (noise). It is not effected by the location of the criterion. Sensitivity is measured by the distance between the centers of the signal absent and the signal present distributions, which is called d'.
Simple reaction time
Is defined as the time between the onset of a stimulus and the beginning of an overt response to it. The actual delay before we can respond to a stimuls is surprisingly long. It takes at least 160ms to respond to a tone and at least 180ms to respond to light. The less intense the stimulus is, the slower the reaction time will be.
Is a stimulus that the others are compared with.
The threshold for the perception of a difference between the standard and the other stimuli. If discrimination is good, the threshold will be small, meaning that small differences between stimuli are noticed.
Point of subjective equality
Is point at which an observer can not tell that two stimuli are different even if they are differnt.
Interval of uncertainty
Stimuli in this region are perceived as very similar to the standard stimulus.
Just noticable difference
The average across the direction of the differences.
Negative time error
When stimuli are presented that are separated in time, the first is judged to be less intense than the later stimulus. Results from the fact that we are judging the currently sensed stimulus against our memory of the previous stimulus and our memories are not as vivid or as sharp as the stimulus currently being perceived.
Describes the relation between the size of the difference threshold and the magnitude of the standard. This constant, which is usually less than 1, indicates the proportion by which a standard stimulus must be changed so that the change can be detected 50% of the time. The larger or more intense the comparison stimulus, the larger the absolute stimulus change must be to be noticed. Turns out to be a remarkably good description of our ability to make discriminations.
Choice response time
Involves making one of several different responses depending on the stimulus presented. If we are forced to respond quickly, the likelihood of making an error will naturally increase.
Speed-accuracy trading relationship
Is a S-shaped curve relating response accuracy to response time. Response accuracy is limited at the lower end of the curve by the probability of guessing correctly by chance. If one pair of stimuli is relly more difficult to discriminate than another pair, then the more difficult pair will result in both lower average response accuracy and longer average response times.
We have it when we are dealing with an experience in which it makes sense to ask 'How much?' or 'How intense?' This and the metathetic continuum are present in the same sense impression.
We have it when we have an experience in which the only question it make sense to ask is 'What kind?' This and the prothetic continuum are present in the same sense impression.
In this, individuals are asked to assign a number directly to the magnitude of a sensation.
Is based on discrimination ability and formed the bassis for the first psychological scales.
Describes the relation between the sensation intensity and the intensity of the physical stimulus. It says that as we increase the magnitude of a physical stimulus, the magnitude of our sensory experience increases rapidly at first, but then more slowly as the stimulus becomes more intense.
Power Law (Steven's law)
Stevens' power law is a proposed relationship between the magnitude of a physical stimulus and its perceived intensity or strength. It is often considered to supersede the Weber�Fechner law on the basis that it describes a wider range of sensations, although critics argue that the validity of the law is contingent on the virtue of approaches to the measurement of perceived intensity that are employed in relevant experiments.
Method of magnitude estimation
People assign numbers that indicate the intensity of their sensation such as loudness and brightness.
In this the observer is aked to match sensation magnitudes across sensory modalities. Example: Squeeze something until the pressure feels as strong as a light is bright.
It s the system for measuring the performance of a communication channel.
Is defined by each necessary question, structured to eliminate exactly half of the alternative answers.
If the observer is presented with a stmulus and gives the correct label as a response, information (the correct label) has been transmitted through the channel represented by the observer. If the response matches the stimulus perfectly for all stimuli, then the observer is a perfect information transmitter.
The human mind is only able to identify about 7 (plus or minus 2) different stimuli that vary along a single physical dimension. It seems that identification accuracy imporves directly as the number of dimensions along whuch a set of stimuli varies increases.
Is the time required to identify the stimulus and is directly related to the difficulty of identification.
States that identification response time is a linear function of the bits of information in a stimulus. It is sensitive to a wide range of fators such as experience with the stimulus, attention, and motivation.
The study of sensation and perception goes well beyond the specific measurement techniques and it is important to understand the basic fundamentals!
Are the basic building blocks of the nervous system. A neuron is a structure consisting of a single cell that can communicate with it s neighbors using a combination of electrical and chemical means.
Conducts information about the outside world to other neurons.
Conducts information between neurons.
Conducts nerve impulses from the central nervous system outward to the muscles.
Contains the nucleus, which includes the genetic material and a large variety of molecules that govern the functioning of the neuron.
Are usually long fibers that conduct nerve impulses toward the many other neurons with which each neuron connects.
The branching structures that receive information from incoming nerve fibers of other neurons.
Neurons that are covered by protective and nutritive cells.
"Glia cells form this sheath around the axon
Is formed by many neurons together and carries information from one part of the body to another.
Central nervous system (CNS)
Consists of the brain and the spinal cord.
Nerves that are within the central nervous system.
Are the tracts in the central nervous system. They are white because of the myelin sheaths.
Regions that appear gray and consist of clusters of many cell bodies.
Information is passed from one neuron to another by electrochemical changes. When a neuron is unstimulated or 'at rest', the inside is electrically negative with respect to the outside. The typical resting potential for a neuron is about -70 mV.
Sodium and potassium are the most important substances for neural action. The pump is an on-going biochemical process.
A change in electrical potential from the resting potential toward 0 mV and beyond.
A change toward a more negative potential than the resting potential.
Action potentials (or neural spike)
Abrupt changes in a cell's state. This process takes only a few ms. Spikes are communicated from one neuron to another more quickly when the axons are large. In myelinated axons, spikes can travel at speeds up to 300 million meters per second!
It is the period following a neural spike and during this time the neuron is much more difficult to excite.
The quantitative changes in a cell's state. For many sensory neurons, the more they are stimulated, the greater is their change in electrical stimulation.
Takes place every time the axons of one neurons ends and the axons of another neuron begins and is a complicted chemical process.
Measures the spike responses of individual neurons. The electrode is inserted into the cell body or the axon, and the potential difference between the test electrode and a comparision electrode located outside the cell is recoded by a computer.
Is used together with a standardized map of the brain of the research animal and allows the researcher to place electrodes in very precise locations in the brain or in a nerve. In general, an increase in firing rate that occurs when a specific stimulus is presented means that the neuron is being excited by that stimulus. A decrease in the firing rate indicates that the stimulus causes an inhibition of the overall activity level of the neuron.
By observing the relation between where a lesion or ablation had occured and which functions are affected, much information can be gained about sensory processing and brain function. Results are often difficult to interpret.
Regional cerebral blood flow (rCBF)
Technique involves injecting into a person a relatively inert radioactive substance that goes where the blood goes without being absorbed.
Is the outer covering of the eye, which is seen as the white of the eye. It is a strong elastic membrane.
Is a simple fixed lens that begins to gather light and concentrate it so that it will eventually form a sharp image on the rear interior surface of the eye.
The colored membrane surrounding the pupil. Is in control of the amount of light entering the eye.
The light enters through this hole into the eye. The size of the pupil is controlled by a reflex. The constriction of the pupil in bright light serves an important function, similiar to that of reducing the size of the aperture in a camera. In dim light, the ability to discriminate details is less important than the increased sensitivity obtained by increasing the overall amount of light entering the eye, so the pupil increases in size and let more light in. When we are really interested in something, the pupils enlarge, as if the eye were trying to gather more light.
Is directly behind the pupil and it s curvature determines the amount by which light entering it is bent.
Is the process by which the lens changes it s focus. When the lens is flat, distant objects will be in focus. When the lens is rounder, near objects are in focus. After about 40 years of age, the ability of the lens to change focus decreases with age because the inner layers of the lens die, causing the lens to lose some of it s elasticity.
Refers to how close an object may be brought to the eye before it can no longer be held in focus and becomes blurry.
Is an eye which has normal accommodative (focusing) ability.
A condition in which the eye is either too short or if the light rays are not bent sharply enough by the cornea, distant objects are seen clearly, but it is difficult to bring near objects into focus -> Farsightedness
"If the eye is too long or if the light rays are bent too sharply by the cornea, near objects are in focus
Phototoxic lens brunescence
Is browning of the lens after long-term exposure to certain UV-B components of sunlight. It leads to a premature aging effect in which the lens takes on a yellow-brown tint early in adulthood.
A screen of neural elements at the back of the eye. Is horizontally organized. Otherwise the many blood vessels providing the photoreceptors blood supply would partially block the light input.
Is a light-absorbing layer in daylight active animals, which lies underneath the retina. This dark layer reduces the amount of reflected and scattered light that could blur or fog the image.
In night active animals the light that penetrates the retina is relfected back through the retina by this shiny surface.
Is the transformation of a phsysical entity (light) into a neural signal.
Transduct the physical energy into neural signal. Humans have two types of photoreceptors. Rods and cones.
Are long, thin, cylindrical cells which are responsible for brightness. NOT located in the fovea.
Shorter, thicker, and more tapered cells. Responsible for colorvision. Are mostly located in the fovea.
Are neurons with two long extended processes. One end makes sysnapses with the photoreceptors and the other end with large ganglion cells.
Are connected to the biopolar cells.
Are closest to the receptors layer. These cells typically have shorter dendrites and a long horizontal process that extends some distance across the retina. Modifies together with the amacrine cells the visual signal and allow adjacent cells in the retina to communicate and interact with one another.
Are found between the ganglion cells and bipolar cells. Modifies together with the horizontal cells the visual signal and allow adjacent cells in the retina to communicate and interact with one another.
Is an imaginary line from the center of the retina that passes through the center of the pupil and here is the most important section of the human retina located.
A yellow patch of pigment located in the region of the origin of the optic axis.
The fovea is critical in vision. Whenever you look directly at an object, it means that the eyey are rotated so that the image of the object falls on the fovea. The photoreceptors are very densely packed in this region. The fovea contains just cones, no rods at all! Outside of the fovea the number of cones decreases rapidly. The number of rods, on the other hand, increases radpidly a sone leaves the foveal region, reaching a peak concentration at about 20�.
Duplex retina theory
Differentiates the visual system in scotopic and photpic vision.
Is the rod system for vision under dim light conditions.
The conesystem which Is for vision under daylight or bright conditions.
People who have no vision in dim conditions. Scotopic vision is entirley dpendent on rods.
These people find normal levels of daylight painful, totally lack color vision, and have very poor visual acuity. Implication is that a functioning cone system is necessary for both normal photopic vision and for the perception of color.
Is the pigment in the rod. It regenerates in the dark with the help of vitamin A. The absence of vitamin A in the diet can show up in epidemics of night blindness. Carrots will indeed your night vision.
Pigment in the cones.
Is the neural pathway from the ling axons of the retinal ganglion cells. It exits from the eye by means of a hole through the retina and the scleral wall. At the center of the optic nerve lie the blood vessels that sustain the metabolic needs of the eye.
Is the region where the optic nerve leaves the retina. There are no photoreceptors in this region.
A region of the retina on which the presence of light alters the firing rate of a cell.
A burst of neural impulses immediately following the onset of a stimulus. Can be thought of as detectors of brightness relative to some average level of intensity.
The cell gives a burst of impulses beginning at the termination of a stimulus. Serve as detectors of relative darkness.
The majority of cells. Small cell body, short branches, dense branching. Slow conduction rate, small receptive fields, color sensitive. May be resposible for detailed form analysis, spatial analysis, and color vision.
Minority of cells, large cell body, sparse branching. Rapid conduction rate, large receptive field, color bind, high-contrast sensitivity. May be responsible for motion detection, temporal analysis and depth perception.
Visual map in the brain. Relative distances and directions between points of lights are preserved, although absolute distances and directions may be greatly distorted.
Information traveling out of the eye along the optic nerves. The two optic nerves come together at a point that looks like an X. All light from the left side of your visual field is mapped onto the right brain and all light from the right side of your visual field is mapped onto the left brain.
Is the oldest visual pathway in evolutionary terms. It is still very important for the perception of motion and for the control of eye movements.
Here a number of fibers from the optic tract branch off oth brain steam instead of to the midbrain. The vast majority of ganglion cells arriving at this location are the magno type in primates. In this structure, information from the various senses is combined and integrated. Structure is in constant communication with higher cortical regions.
Signals which represent feedback based on previous information that has already been sent to the brain. Magnocellular type cells.
Is the dominant pathway for humans and other primates. The devision into two parallel streams of processing that began in the retina - a slower-acting one for detailed form and color vision and a faster-acting one for movement perception - continues into the brain.
Lateral geniculate nucleus
Is a structure in the thalamus and the major termination for the optic tract in the primary visual pathway. It is arranged in six layers. Cells in this structure neceive neural signals not only from the retina but also from higher visual centers in the cortex.
Is a form of large fan of fibers which consists of the axons of the lateral geniculate neurons that leave the geniculate.
Visual Area 1 (or Primary visual cortex or striate cortex)
Is the most important cortical visual region because it is the first stop in the cortex and almost all of the signals received by the other cortical regions pass through it and are returned to it by back projections. It segregates three major types of visual information - form, color, and motion - and routes these outputs to separate cortical regions for processing.
Is the foveal region of the retina in humans.
Visual Area 2
Visual area V2, also called prestriate cortex, is the second major area in the visual cortex, and the first region within the visual association area. It receives strong feedforward connections from V1 (direct and via the pulvinar) and sends strong connections to V3, V4, and V5. It also sends strong feedback connections to V1. V2 cells show a small amount of attentional modulation (more than V1, less than V4), are tuned for moderately complex patterns, and may be driven by multiple orientations at different subregions within a single receptive field.
Examining the anatomical structures of the cortical cells.
Is the relationship in area V1 that the neurons at the center of the visual map are able to register much finer details than those in outer reaches of the map.
Condition in which a patient is blind to a part of the visual field when the corresponding piece of visuall sensitive primary cortex is damaged.
Is the complete loss of vision as the result of occipital lobe lesions.
They have generally little spontaneous activity and never seem to respond to diffuse illumination covering the whole screen. The stimulus that really gets them firing vigorously is a dark or light bar that is flashed in the appropritate location and orientation in the receptive field. Thus they seem to have Orientation specificity.
It is more complex in the sense that it will respond to an edge of particular orientation regardless of where that edge appears within the visual field. As a result, complex cells have larger receptive fielnds than do simple cells. Complex cells prefer the edge to be moving in a direction that is at 90 degress to the orientation of the edge.
Found in area V1. It s receptive field not only responds to an edge of a particular orientation, moving in a certain direction, but it does so only when the edge is of a specific length. Cells with these receptive field properties are not randomly intermixed in area V1.
Blobs�are sections of the visual cortex where groups of neurons that are sensitive to color assemble in cylindrical shapes. These areas receive input from parvocellular cells.
Interblobs are areas between blobs which receive the same input, but are sensitive to orientation instead of color. They output to the pale stripes of area V2.
A region of cortex containing all 360 degrees of orientation specificity, and including a region responsive to both the left eye and the right eye.
From V1, axons send neural messages directly and in parallel to many other visual maps. These other visual areas in the cortex are referred to as prestriate cortex.
Because area V1 and V2 represent visual information in similar ways and because both of these visual ares send axons to almost all of the other prestriate visual areas, these two areas are refered together.
"Contains a visual map, separate from areas V1 and V2. It is a complete point-to-point correspondence map of the visual field. Their receptive fields tend to be specific for edges of particular orientation
V4 is tuned for orientation, spatial frequency, and color. Unlike V1, V4 is tuned for object features of intermediate complexity, like simple geometric shapes, although no one has developed a full parametric description of the tuning space for V4. Visual area V4 is not tuned for complex objects such as faces. May be important for perceptually glueing the color onto the objects rather that it belongs to, and thus establishing clear boundaries between regions of the visual field.
A loss of color vision only to one side and at other times complete color vision loss.
Is specilized for detecting the speed and direction of motion. All neurons in V5 are senstive to color. They are senstive to the overall direction of motion of an entire object. The neurons have very large receptive fields.
Unability to predict the speed of approaching objects.
"Seems to be specialized to answer the question ""Where is it?"". From the occipital lobe to the parietal lobe. Also called dorsal stream."
Condition in which a patient is able to recognize an object but not reach for it.
"Answers the question ""What is it?"". From the occipital lobe to the temporal lobe. Also called ventral stream."
The lower temporal lobe.
Inability to identify objects just by sight.
These patients can see all parts of the visual field, but the objects that they seen mean nothing to them.
Superior tempral cortex
Neurons in this region have been found to respond selectively to faces and to particular movements of faces.
Dynamic receptive fields
It turns out that neurons in V1 have receptive fields that are much more dynamic than was originally thought. This view suggests that individual visual cortical neurons are part of a network, or a complex circuit and that a given cell may change it s tuning from one situation to another.
Vision depends on the presence of light. Photometric units are used to describe light, and these units are, by convention, expressed in terms of enegy. There are two ways by which light can reach the eye: (1) Directly from a radiating source such as light bulb (2) Indirectly by reflection from surfaces that have radiant energy falling on them.
Is the amount of energy coming from a light source.
The unit of radiance.
Is the amount of light falling on a surface.
The amount of light reflected from a surface.
The percentage of light falling on a surface that is reflected.
The amount of light reaching the retina.
The phenomenal impression of the amount of light that is being emitted from a source or reflected from a surface. Is the psychological attribute corresponding roughly to the physical measures of illumiance and luminance. Depends on the current stat of sensitivity of the eye.
The phenomenal impression of the percentage of reflected light relative to the total light falling on a surface.
Is the unit of brightness. Each bril represents about 1/10 of a log unit above threshold of detection for a human observer.
Is adaptation to darkness and takes much longer than adaptation to bright environments.
Is the adaptation to bright environments.
Is daylight vision provided by the cones. Cones quickly reach their level of maximal sensitivity while rods take longer to adapt.
Is twilight vision provided by the rods. Rods are more senstive to light but at the expense of giving up color vision.
Is the change in the brightness of light of different wavelenghts as the intensity is changed. We are more sensitive to blue-green light under dim viewing conditions. Red light is virtually equivalent to no light at all for the rods. Thus pilots get briefed under red illumination, then function efficiently in the dark without waiting the many minutes necessary to completey dark adapt by the rods.
Describes the photochemical reaction of any light-sensitive substance, whether it be film or visual pigments.
This means that a weak stimulus must be presented for a long time in order for it to be detected, whereas a more intense stimulus can be presented for a shorter duration and still be detected. The size of a stimulus also affects ist detectability. Increasing the stimulus size might be thought of as simply filling in the center of the receptive field with light, thus adding more on responses to the overall activity.
Describes a tradoff relationship between area and intensity. Fluctations of only a few photons may affect our perception of brightness.
Simultaneous brightness contrast
Our perception of the brightness of targets often depends more on the luminance of adjecent object than on the luminance of the target itself.
The fact that a light surround depresses the apparent brightness of a target suggests that some form of spatial interaction is present. This interaction must invovle some form of inhibition, where an actively stimulated portion of the retina will suppress other nearby retinal activity. The more a neuron is stimulated and the closer it is to another neuron, the more intensely it will inhibit each other. In the part of the retina exposed to the lightest surround, many neurons are active and are actively inhibiting their neighbors. This inhibition from the light surround should reduce the response of the receptors exposed to the inner square, making it appear dimmer.
Two bands of blurry lines are visible at the points marked by the arrows in a figure. One is darker than any other part of the figure and the other is brighter. Their presence can be explained by lateral inhibition. The physiology of the retina implies that inhibitory effect should take place over a limited distance and that targets that are relatively far away from one another should not be affected. But this is not the case!
This principle suggest that the highest luminance in a pattern tends to appear white and serves as a standard by which all of the other luminances are perceived. When the highest luminance increases, the standard against which the others are judged is raised and all other surfacces in the scene appear to be darker, not because they have changed, but rather because they are now darker relative to the highest one.
High-level cognitive processing and computational mechanisms may play a role in other brightness phenomena. The revers of brightness contrast is called brightness assimilation. There is evidence that how we distribute our attention over a pattern influences whether brightness contrast or brightness assimilation occurs. In general, the part of the visual field to which we are attending - or at least the part that is viewed as the figure or object, rather than the background - shows greater brightness constrast. Regions that are not directly attended to then show brightness assimilation.
The color stimulus
"Color vision might have evolved in our history in response to a specific environment. Colored light does not exist
Color circle (or Color wheel)
In this arrangement, the separated colors are separated according to their hue.
Is the psychological dimension that most clearly corresponds to variations in wavelength.
Stimuli which contain only one wavelength.
Stimuli which are generated by Newton's prismatic separation of light.
Color spindle (or Color solid)
Combines the three psychological attributes hue, saturation, and brightness.
Used to catalog the various colors in which each page represents a horizontal or a vertical slice through the color solid.
Are colors that appear to be the same even though they are really made up of different wavelengths of light.
Combining three of these colors create a color that perfectly matches another monochromatic color.
Additive color mixing
The process of combining different wavelenghts of light in order to produce new colors.
Substractive color mixing
Is mixing paints in order to produce new colors. Each addition of pigment to the mix results in more wavelenghts being absorbed by the pigments and thus in less light being reflected toward the eye of the observer. You are essentially subtracting all of the wavelenghts, leaving only a muddy gray appearance.
Are colors whose mixture produces an achromatic gray.
CIE chromaticity space
Can represent any color as a point in the color space. It has been arranged so that y represents the proportion of green in the mixture and x represents the proportion of red in the mixture. For example, if we had a color specified as 0.2x and 0.6y, we would know that it is composed of 20% red, 60% green, and (substracting 80% from a total of 100%) 20% blue.
By this any color stimulus is specified in the CIE color system. It is simply the x- and y- coordinates for the hue of the stimulus and the z-coordinate for the brightness of the stimulus.
Describes those colors that can be produced by a particular TV or monitor screen.
We can deduce cones are the retinal receptors that provide the first stage of color response. We can differentiate million of different colors and we need only a few different retinal receptors, each with a different wavelength sensitivity to do so. It is suggested that there are three types of receptors, one responsive to long wavelenghts (L cones), one for medium wavelenghts (M cones), and one for short wavelenghts (S cones). This theory finds very convincing support from studies of people with defective color vision.
According to the trichromatic theory of color vision, we can predict different varieties of color abnormality. Color defects are genetically transmitted on the X chromosome.
Individuals with a malfunction on only one type of the cones. They should be able to match all other colors with a mixture of only two primaries. There are 3 forms of this condition.
Individual would be insenstive to long wavelenghts normally perceived as red light because his L cones are not functioning properly.
"Individual have a malfunction in the M cones. They are still able to respond to green light
Absence or malfunction of S cones. Individuals see the long wavelenghts as red and the shorter ones as bluish-green.
Colors matched by these individuals require more red or more green than do color matches of normal observers.
Physiological basis of trichromatic theory
In general: In humans there are three major groups of cones. There are virtually no S cones in the central fovea region, which suggests that all observers are dichromats for small targets seen in central vision. The relative rarity of S cones probably also explains why blue contributes less than red or green to many aspects of the visual process. In the far periphery of the retina, we are totally color blind.
With this device a norrow beam of monochromatic light is focused on the pigment-bearing outer segment of a cone. As tiny amounts of light of various wavelenghts are passed through the cone, the amount of light absorbed at each wavelenght is measured. The more light of a given wavelength is absorbed by the cone pigment, the more sensitive is the cone to light of that particular wavelength.
Are intermediate light levels when both rods and cones are active to some degree.
Are women who have one cone type more than other individuals. They are more color senstive than normal persons.
Are neural processes in which four primate colors (red, blue, green, and yellow) are arranged in opposing pairs. One opponent process would signal the presence of red or green, and a separate process would signal blue or yellow.
Physiological basis of opponent-process theory
Neural responses are subject to both excitatory and inhibitory influences caused by interaction between neighboring units. By the time the analysis reaches the level of the retinal ganglion cells, there is clearly an opponent-process coding.
Account for around 70% of the geniculate neurons. Contains opponent-process neurons. Contains L-M (red-green) opponent neurons.
Account for about 10% of the neurons. Seems to be specialized in carrying brightness information.
Neurons which are interleaved between the parvocellular layer and account for 10%. Contains opponent-process neurons.
These are perceived colors, in the absence of the appropriate wavelenghts of the light, that can be made to appear in a certain flickering black-and-white display. May arise because of the interaction between the magnocelluar system, which carries brightness information, and the parvocelular system which carries color information. The latter system is slower and still responding after the magnocellular system has indicate that a flash of colorless light has come and gone.
Blue-greens and violets begin to appear bluer when the intensity is increased. Comes about because the red-green opponent-process cells are slightly more sensitive than the blue-yellow cells.
Proloned exposure to colored stimuli also produces a shift in the perception of hue. This fatigue of a specific color response are due either to selective bleaching of one particular photopigment or to fatigue of one aspect of the neural response of an opponent-process system.
Are fatigue effects due to prolonged stimulation localized to only one region of the retina.
Simultaneous color contrast
Inhibitory interactions between adjacent color systems which can result in hue shifts.
Color assimilation effect
Is very similiar to the brightness assimilation effect.
Cogntive factors in color perception
We remember colored scenes better than black-white scenes. The remembered color of familiar objects often differs from the object's actual color. Patients suffering from depression are more likely to agree that the lights in their surroundings seem dimmer than usual. Color is a psychological achievement, not simply a direct effect of the physical variaton of wavelengths of light.
Results from air compression as a guitar string moves forward and rarefraction as it moves back. Sound waves can be transmitted for great distances even though the individual molecules of the medium vibrate only over very small distances. This is done when air molecules collide with those next to them, thus moving the pressure wave through space. Each of these collisions loses a bit of energy, so the pressure variations are less intense as the sound wave moves away from the source.
Is a simplest sound wave, a sine wave.
Is the distance from one peak of the wave to the next, which also represents a single cycle from one maximum pressure through a pressure minimum and back to the maximum again.
Is the number of cycles completed during one second.
Is the measure of frequency. One Hertz is equivalent to one cycle per second.
Is the change in pressure produced by the sound wave.
1 bel equals 10dB.
Is the measure of sound pressure levels. Loudness increases as the sound pressure level increases. Sound pressure amplitude is the most important determinant of loudness.
Refers to the particular part of the comprassion-refraction cycle a wave has reached at any designated instant of time. Any point in a cycle can be specified by number of degress from 0� to 360�.
If two pure tones are at exactly the same place in their respective cycles they are in phase. If two pure tones are perfectly in phase, their pressure changes coincide and the amplitude of the resulting tone is the sum of those of the two tones.
Is the difference between the phase angles of two pure tones.
Active noise suppression
Uses the principle that ti out of phase tones also have the same pressure amplitude, they actually cancle each other completely. Thus unwanted sounds can be eliminated.
An additional psychological property of complex sounds. Means that two different instruments produce different wave forms even when they re playing the same musical note.
Refers to decomposite a complex waveform into a set of sine waves.
Ohm's acoustical law
Refers to the fact that the ear forms a mechanical Fourier analysis on complex sounds, allowing us to hear the various simple sounds that went into a complex sound.
Internal structure of the ear in fishs which is filled with fluid and there are tiny hairs that protrude into the fluid and bend when it moves in response to sound stimulation from the water outside.
The labyrinth became the cochlea in mammals, birds and crocodiles.
What you see from the ear from the outside.
The fleshy part of the visible from the outside. Affects sound localization.
Ear canal (or External auditory meatus)
Acts as a passive amplifier increasing the amplitude of certain sound frequencies through resonance.
Eardrum (or tympanum)
Vibrates to transmit the sound waves.
In this, the vibrations of the ear drum are transmitted by three tiny bones. Increases the pressure applied to the oval window. The structures in the middle ear amplifies the vibrations which are transmitted by the eardrum by a factor of about 30. But it can also decrease the pressure at the oval window relative to that of the eardrum. It is a protective mechanism designed to reduce damage to the ear.
The three tiny bones Malleus (Hammer), Incus (Anvil) and Stapes (Stirrup).
A small membrane-covered opening in the middle ear. Is the boundary between the middle and inner ear.
When the tiny bones in the middle ear cannot conduct sound vibrations because they are fused together of because there is a break in the chain connections this condition results.
The pressure of the air in the middle ear is kept approximately equal to that of the surrounding atmosphere by this. A pressure differential would cause the eardrum to bulge and stiffen resulting in less responsiveness to the sound striking it.
A condition in which bacteria travel to the middle ear and cause infections that can also result in temporary hearing loss.
The inner part of the ear that has three tubes.
Is the first tube in the inner ear and thus at the oval window. It s far end is called the apex.
Another tube in the inner ear which is connected to the apex. It has it s own membrane-covered opening at it s base, which seperate it from the airspacce in the middle ear.
Is the membrane-covered opening at the tympanic canal base, which seperate it from the airspacce in the middle ear.
Is a fluid in the tubes of the inner ear that resambles salt water.
Is the third canal of the cochlear. It is formed by two membranes.
Is only two cells thick and has no function other than to form one wall of the cochlear duct.
It supports the movements of the cochlear fluid into neural signals.
Is a third mebrane in the cochlear duct that extends into the cochlear duct from Reissers membrane.
Organ of Corti
Some hairs of this structure are embedded in the tectorial membrane. It contains hair cells that covert mechanical action in the cochlea into neural signals that are sent to the brain.
Inner hair cells
The hair cells transmit the energy. A single row of about 3000 of them is found on the inner side of the cochlea.
Outer hair cells
There are five rows of outer hair cells in the cochlea.
Each hair in a bundle is connected to nearby hairs in the same bundle by linking filaments. Because of these links, all of the hairs in a hair bundle tend to move together. This is important for the transduction of sound in the organ of Corti. There are evidences that hair cells can be stimulated to regenerate even in humans!
Receives about 30000 nerve fibers which make connections with the base of the hair cells in the cochlea.
Type 1 fibers
95% of the nerve fibers which make connections with inner hair cells. The have large diameter axons and are covered with a myelin sheath that allows them to conduct neural impulses considerably faster than do the small-diameter, unmyelinated type 2 fibers.
Type 2 fibers
5% of the nerve fibers which connect to outer hair cells. Type 2 fibers might carry different information than type 1 fiber.
Is a part of the brain steam that sends signals to the hair cells. Thus the hair cells not only send sensory (afferent) information to the central nervous system vie the spiral ganglion but also receives out-going (efferent) signals.
Mechanical tuning on the basilar membrane
When the stapes vibrates against the oval window, it causes the fluid to move down the vestibular canal. This vibration eventually reaces the helicotrema and then moves around the bend to cause fluid motion in the tectorial canal. Together these movements cause a sort of shearing action that produces pressure waves across the chelear duct. These pressure waves, in turn, cause mechanical waves to travel down the basilar membrane from the stiffer, narrower base to the looser, broader apex.
Provides additional tuning by modifying the mechanical vibrations before they reach the inner hair cells, thus sharpening the mechanical tuning of the basilar membrane. The hair themselves add the required energy to their own motion when stimulated with a motion to which they are tuned. In mammalian hearing, the outer hair cells are the source of the mechanical amplification.
Means that sounds are actually emitted by the ear. Arise from the operation of the active process that amplifies the traveling waves. Is eliminated by admistering aspirin in monkeys. Drugs that reduce the ability of the outer hair cells to move also reduce otoacoustic emissions, suggesting that these internally generated sounds may arise from the activity of the hair cells.
Refers to the process of changing mechanical vibrations in the ear to into electrochemical fluctations, which are the code of the central nervous system. It happs in the organ of Corti. The bending of hair cells is transducted into electrical changes in the hair cells by a mechanism that involves the tip links that go from the shorter hairs to their longer neighbors. Potassium ions, which have a positive charge, flow into the hair whenever one or more pores are open. This causes a depolarization that may go up to 20mV. This electrical event triggers the release of neurotransmitter substances from the bottom of the hair cells. These neurotransmitters stimulate the dendrites of the spiral ganglion cells, which then generate the action potentials that go up the auditory nerve to higher brain centers.
Electrical activity of the auditory nerve
After transduction in the cochlea, the information in a sound is encoded into patterns of electrical activity in the auditory nerve. The axons from spiral ganglion neurons make up this auditory nerve.
Threshold response curve
Refers to curves which results from the variation in sensitivity with the frequency of the sound.
Each neuron has it, for this it s neural absoulte threshold is lowest.
Neurons that respond to pure tones.
Shows how the firing rate of auditory neurons in response to a tone of constant intensity varies as we change the frequency of the tone. Auditory nerve tuning arises from the mechanical properties of the basilar membrane and the active process.
Demonstrates the effect that outer hair cell responses have on the responses of the inner hair cells. Arises from mehanical actions of outer hair cells stimulated by the second tone that act much like lateral-inhibition in vision. This reduce the response of the basilar membrane nearby and thus diminish the response intensity that the inner hair cells would normally procude for the frist tone.
If the stimulation continues unchanged, the firing rate drops over time, eventually reaching a much lower rate near the background rate. The various phases of adaptation correspond to various stages in the depletion of available neurotransmitters at synapses with the inner hair cells. The long-term adaptation effects are thought to be the neural basis for auditory perceptual adaptation, which is the decrease in the perceived loudness of a low-level pure tune that is listened to for a long period of time.
Each neuron would tend to fire in phase with the sound wave, although one may fire iony about every second peak, whereas another fires only about every fifth peak.
Altough tuned neurons do fire more rapidly as the sound pressure level increases, they only do this up to about 30 to 50dB above their threshold. At this point, the neuron is firing as fast as it can, it is saturated. But the greater a sound's pressure amplitude, the more individual neurons will fire in response to it.
Used to comensate for deafness caused by non-functioning of the hair cells. A computer sends tiny electrical signals to the electrodes to stimulate the auditory nerve to fire similary to the way it is made to fire by the hair cells in normal-hearing persons.
Interconnection between areas in the brain.
The axons from the spiral ganglion neurons that make up the auditory nerve projects to this.
Ventral cochlear nucleus
Neurons here send half of their axons to each side of the brain in the superior olive.
Dorsal cochlear nucleus
The axons here cross all over to the opposite side of the brain. Thus it appears that much of the auditory information from the right ear is initally sent to the left side of the brain and vice versa.
Primary auditory projection area (or A1)
Is a part of the superior temporal cortex.
Auditory where and what streams
There seems to be a general division of the auditory system into what and were subsystems.
They give a burst of responses immediately after the onset of a tone and then cease responding, no matter how long the tone persists.
Exhibit a similar burst of firing at the onset of a tone but this is followed by a pause and then a weaker sustained response until the tone is turned off.
Give repeated bursts of firing followed by short pauses with the vigor of successive bursts decreasing.
Give an inital vigorous burst of firing when the tone is turned on.
Reduce their response rate below their spontaneous activity level at the onset of the tone and then give a burst of activity at it s offset.
Is the response of the basilar membrane. Because different points along it vibrate most stronlgy for different frequencies of sounds. It produces a frequency map where progression across the cortex is associated with a systematic rise or fall in frequency responsiveness.
The right auditory cortex is specialized for processing slowly changing narrow-band sounds, like melodies, whereas the left auditory cortex is specialized fro processing more rapidly changing sounds like speech. The left cortex is even active when lip reading without auditory stimuli! The organization of the auditory cortext changes with expriences. It is invaded by visual and touch processing in the early dead and it also changes over relatively short periods of time with conditiong and learning.
Frequency sweep detectors
These neurons respond only to sounds that change frequency in a specific direction and range.
Is the difference between the absolute threshold (ear is most senstive to frequencies between 1000 and 5000 hz) for hearing and the pain threshold of the ear for any given frequency of sound.
The required amount of engery required for hearing can arrive as a high pressure over a short time interval or as a lower pressure over a longer interval. Hughe's law describes this relationship.
There is a critcal duration beyond which temporal summation does not occur, there is a critical band of frequencies beyond which adding tones does not failitate detection. The critical band is much narrower for low frequencies than for high frequencies.
Sound presentations to one ear.
Sound presentations to two ears. The threshold for them is about one half that for monaural presentation. Binaural thresholds can be lower than monaural threshold even if the sounds are not presented simultaneously to the two ears.
Happens when sound we want to hear is obscured by sound we don't want to hear. The greatest masking effects is found for tones with frequencies similar to that of the masker. If sounds are separated by more than about 300ms, there is no measurable masking. If is likely that the masker is lowering the sensitivity of the hair cells, or their synapses with auditory nerve fibers, thus raising the threshold of the target.
When target and masker are presented at the same time, this masking occurs.
Upward spread of masking
While there is also substantial masking of tones higher in frequency than the masking sound, tones of a lower frequency are relatively unaffected by the masker. Tones of higer frequencies produce vibration patterns nearer to the oval window.
Occurs when target and mask are presented simultaneously to different ears, although the masker must be about 50dB more intense than in simultaneous masking.
The Weber fraction for sounds is smallest for stimuli in the middle range of frequencies (1000Hz to 4000Hz). The sound pressure-difference thresholds are about 33% smaller for sounds presented simultaneously to both ears than for those presented only to one ear. This is because the binaural presentation gives the observer two chancces to hear the difference. Binaural frequency difference thresholds are about 33% smaller than are monaural ones.
Our auditory systems construct a sort of auditory space to localize sounds with our bodies at the center. Azimuth is the angular difference from the straight-ahead direction.
One ear receives the sound a direct path from the source whereas the other ear is in the sound shadow. The shadowed ear receives only those sounds that are bent around the hear or diffracted by the edge of the head.
Sound level difference
The sound pressure at the the shadowed ear is lower than that the the ear receiving the sound directly. Sound level difference between the ears is larger the farther the source is from 0� azimuth. The increase in sound level difference with increasing azimuth serves as a cue to the direction the sound came from.
Describes the difference between the arrival of the sounds at the two ears.
Two process theory of sound localization
It is suggested that we localize low-frequency sounds by using time differences at the two ears caused by differences in distance from the source, while we localize high-frequency sounds by using the sound intensity differences at the two ears caused by the sound shadow.
Minimum audible angle
Is the smallest amount of spatial separation of two sequentailly presented acoustic events that can just be detected.
The fusion of sounds and their early echoes into one auditory event, and the localization of that fused sound at the source of the earliest-arriving sound.
Sound which has a distinct quality, like an echo, is a cue to the distance of a sound source from an observer.
Observers seem to correct for the fact that actual sound pressure diminishes rapidly as the distance from the sound sourc icreases.
Head-related transfer function (HRTF)
Is a mathematical description of exactly how each frequency in a sound is amplified or damped by the body parts near the ears, depending on it s direction. It describes all of the information avaiable at the two ears regarding the location of a sound source. HRTFs of different people are of course different. However, humans are sufficiently similar so that a generic HRTF can be created.
Different neurons are tunes to particular time or intensitiy differences. It is possible that such neurons constitute a kind of map of auditory space, with each neuron having a region of auditory space to which it responds best, a sort of auditory receptive field. The auditory map could be based on, or at least calibrated by, the more precise map of visual space. Maybe the neurons just pass the information to higher cortical centers for computing sound localizations.
Is a subjective dimension that is thought to directly reflects sound pressure. However, depends on interactions of serveral factors.
Is thought to reflect sound frequency.
A loudness of 1 sone has any sound whose loudness matches that of the standard sound, a 1000Hz stimulus at a level of 40dB.
Equal loudness contour
Shows the sound pressure levels at which tones of different frequencies appear to be equally loud as a standard tone. For tones briefer than about 200ms, we must increase sound pressure level of a shorter tone to match the loudness of a longer tone.
Spectral loudness summation
The summation of loudness across critical frequency bands by the auditory system.
All are frequencies in some range.
Refers to the pitch of isolated sounds, or at least sounds in a nonmusical context. The most important physical determinant of acoustical pitch is the frequency of the sound stimulus. Varying the pressure level of a tone alters it s pitch.
The lowest frequency, and usually most intense, pure tone in a complex sound. Determines the pitch of a complex sound.
Have a higher frequencies than the fundamentals. Are muscally overtones. Determines the timbre of a sound.
The pitch of a sound with this characteristic sounds the same as the pitch of a sound that contains both fundamental and harmonics.
Asserts that different pitches are encoded as different places of maximum vibration along the basilar membrane. Has difficulties explaining the missing fundamentals illusion.
Asserts that pitch is encoded in terms of an overall frequency of firing in the auditory nerve. Pitch is determined by the overall pattern of spike potentials traveling up the auditory nerve, the number of which rises and falls depeding on the number of spiral ganglion neurons firing at any moment. According to it the missing fundamental is signaled by the neurons that respind to harmonics below 4000Hz.
Describes how neurons fire in groups or squards. An increase in the pressure of a sound, although not changing the volley frequency, would increase the number of neurons firing at each pressure peak, both by stimulating additonal neurons that had not previously been firing and by increasing the firing rate in those neurons that were not yet saturated.
May consist of any number of sound-producing events. Each sound source or event varies in spectrum, duration, location, time, and so forth.
Auditory scene analysis
We must build separate mental representations of the events from the sound mixture we receive. To do this, we must infer backward from the mixture of sounds we receive to the events that generated them.
Is a fast, involuntary, probably innate process. Sounds that have similar patterns over time or that have similar frequency spectrac are grouped into separate auditory streams. Can create illusions.
"Are higher level hypotheses or expectations based on knowledge of familiar sounds. These schemas are learned through experiences. It takes longer to operate than the grouping processes do
Intended to say
The goal of speech perception is to develop in the listener's consciousness a meaningful representation of what the speaker intended to say. Speech is special, there are special mechanisms for producing and perceiving speech.
How each speech sound is produced.
How specific sounds distinguish words in a language.
A speech sound that is used in language to distinguish one word from another.
They arise because the sound waves created by the passage of air from the lungs across the vocal cords and out through the articulators are affected by the position of the various parts of the vocal tract. For the same vowel sound corresponding formants are located at higher frequencies for the child than for the adult.
Is the idea that for each phoneme in an utterance we should be able to find a corresponding segment of the physical speech signal.
The notion that there must be some constant set of acoustic features associated with each perceived phoneme.
Is speech special?
There is a distinct difference between our perception of speech and of other sounds and speech perception is accomplished by a specialized set of neural mechanisms in humans. But at least some of the special properties of speech sounds are not specific to humans. It is yet not clear how special speech perception is and how much of what is heard is in the signal and how much is constructed in the mind of the listener.
Is the experience of percept invariances in�sensory phenomena�that can be varied along a continuum. Consonants show it, vowels do not.
The value of voice onset time that devides a voiced b region from an unvoiced p region.
When the visual and auditory inputs are incongruant, the percept is often a compromise phonetic percept. In this case 'da'. But we don't need visual cues to understand speech.
In this affects what we see what we hear.
The context in which speech occurs can serve the function of embadding as t often does for vision. The possible meaningful words that can occur in speech provide a context that influence what is perceived in an ambiguous speech stimulus.
Are words that sound alike when spoken but convey different meanings.
Phonemic restoration effect
Restored phonemes can cause shifts of phonemic categorical boundaries. We hear the speech units that the immediate context suggests should be in the phrase, even if they are not physically present.
Feature detectors (or Template matching)
Feature detectors for speech are usually conceptualized as neurons specialized for the detection of specific aspects of the speech signal. An auditory template may be viewed as a stored abstract respresenation of certain aspects of speech that develops as a function of experience and serves the same function as a feature detector.
Usually postulate several stages of processing.
An active model of word identification. In this model passive anaysis initally identifies the phonemes of a word. These then activate a corhort of words in memory that have similar phonemes. At the end, all words in the cohort are eliminated except the most appropriate one.
Implements passive feature detection at three interacting levels (1) Acoustic feature detectors whose output is the input to (2) phoneme detectors whose output is the input to (3) word detectors.
Has both active and passive elements. In this theory, perception of speech sounds is accomplished by a special processing mode that is both innate and part of a more general specialization for language that humans possess.
"Or edges are sudden changes in light intensity across space. Specific cells in V1 are edge detection cells that signal in the presence of a contour. Contours are the basic building blocks of visual perception
Shapes are separated from the background or from other shapes by contours.
Is a region in the retinal image where the light intensity changes abruptly. Examples can be found at the edge of a blackboard or the outline of the moon against the night sky.
Emergent (or second-order contour)
These are contours, which are not physically there but constructed by the perceptual system from the first-order contours that are present. Also called subjective contours. Created by pregnanz combined with other organization processes.
Is a visual field that contains no abrupt luminance changes and thus no contours.
Natural blank out: Snow blindness. A feeling that you can't see, after prolonged viewing, but this is not attributable to any loss in the ability of the individuals to detect changes in luminance if they do occur.
Refers to the ability of the eye to resolve details.
Test of visual acuity, is measured with a Snellen chart of letters.
Is a measure of the size of the retinal image.
Vernier (or directional acuity)
Requires an observer to distinguish broken lines from unbroken.
Resolution (or grating acuity)
Is measured by an observer's ability to detect a gap between two bars or the orientation of a grid of lines.
Resolution of details less than about 10 sec of arc. In this case, the visual performance seems to have gone beyond the resolution imposed by the physical size of the receptors. It might exist because high-level cells are specifically tuned to particular acuity details, like gaps, breaks, or offsets.
Factors affecting visual acuity
Acuity is best in the central fovea and drops off rapidly as we move into the periphery. The part of the retina that is highest in visual acuity contains mostly cones, which send their signals to parvoganglion cells. Because cones operate only at high lights of illumination, we could then predict that there would be better acuity at high lumination levels.
Is the tendency to accomodate the eye inappropriately near, even when the object of interest is far away.
Implies that it is possible to analyze any pattern of stimuli into a series of simpler sine wave patterns.
Sine wave grating
Each pattern of the stimulus is seen as a regulary varying pattern of light and dark if seen alone. By adding together a number of sine wave gratings we can produce any specific light distribution.
Square wave grating
In this grating, the light changes are sharp and give a boxlike intensity pattern.
Spatial modulation transfer function
Is a graphic or mathematical description of the way in which certain spatial frequencies are accurately reproduced while others are lose because the system cannot resolve them.
Is a measure of the difference between the highest and the lowest luminance levels in a pattern.
Is the difference between maximum and minimum lumiance levels divded by some average or pooled estimate of the overall amount of light.
Used to measure the modulation transfer function in humans.
Is the amount of contrast needed for you to detect that there is a grating present in a pattern, rather than a uniform gray. Sensitivity decreases rapidly for higher spatial frequencies, meaning that we need more contrast to see these stimuli. The eye is an optical system, containing a lens, and any such system has a high-frequency cutoff. Our sensitivity changes when we grow older.
Neural spatial frequency channels
The first stage of spatial frequency analysis can be accomplished by retinal receptive fields. Every receptive field is tuned to a sine wave frequency whose half cycle is equal to the size of it s cental excitatory or inhibitory region. Two types of responses tend to cancel each other out, thus the total response of the ganglion cell with this receptive field is low. There may be a number of different channels in the visual system, each tuned to a different range of spatial frequencies. There is some evidence that the magnolike low spatial frequency channels interact with and can inhibit the parvolike higher spatial frequency channels.
The neural mechanisms that could perform a Fourier analysis of a visual image. They are filtering out all but a select set of stimuli and passing on information about only those to which they are tuned.
Difference of Gaussian filter (DOG)
Spatial filter that results from the combination of excitatory (meaning that neural responses increase toward the center of the filter's field) and inhibitory (meaning that neural responses actually decrease the likelihood that other nearby neurons will react).
Is a combination of a bell-shaped Gaussian distribution with a sine wave, and the important result of this is that it results in a new kind of filter that has an orientation in two dimensions can can produce responses that look like the orientation specific neurons in the visual cortex that respond best to bars or edges with a specific tilt.
Explanation: A receptive field that is center-excitatory and aligned with an intersection will have a larger net amount of inhibition in it s surround than will a same-size receptive field centered in the space between two squares. This means that, the intersections will be registered by the ganglion cells as containing less light than the vertical and horizontal regions between squares. The illusion does not occur when the interesections are being fixated directly because the receptive fields are smallest for neurons in the fovea region of the retina and they increase in size with distance from the fovea.
Is the reduction of our visual acuity for any one of the group of contours. The same excitatory and inhibitory neural interactions that enhance the visibility of contours make it more difficult to perceive contours under certain conditions. Crowding effects are much greater in certain clinical conditions. The crowding phenomenon is a kind of simultaneous masking because the target stimuli ad those that flank it are presented at the same time.
Clinical condition, which is associated with diminished visual acuity, often in one eye, but usually without any obvious visual pathology. May result from a failure of the neural contour detection and enhancement mechanisms at the level of the organization of simple reciptive fields.
Refers to a reduction in the visibility of a contour or target that is caused by the presentation of a second stimulus that is close to the target in space and/or time.
A masking stimulus that consists of some array of contours that overlap the same position in space.
A masking stimulus that contains closely adjacent but non-overlapping contours.
Interstimulus interval or stimulus onset asynchrony
Is the time between the presentation of the target and the presentation of the mask. This determines what you actually see when the target and the mask are seperated in time.
Affecting the visibility of a target that was presented earlier and is now gone. Is strongest when a brief interval of about 50 to 100 ms intervenes between the presentation of the target and the mask.
In the natural world the perception of contours can be very complex. In order to analyze an image appropriately, the visual system must be able to group contours that truly belong together. There is a cooperative grouping process in human vision that seeks to extend edges as well as a competitive grouping process that do not have the same orientation. For contour perception to occur, there must be not only spatial variation in the intensity of light but also variation over time in the pattern of illumination on the retina.
Is the representation of the original image in which only the edges have been preserved and coded as points.
Differentiate shapes in our consciousness from other shapes.
Those feature that help you to differentiate one stimulus from another.
In this task, an observer looks for the presence of a single target item in an array. When the identification of the target is independet from the number of distrecter items, then the target is said to pop out and the feature that differentiate the target item from the others is though to be a basic visual feature.
Simple features which are combined in a hierarchical fashion.
Figures that cannot be explained by simple examining the component parts. The Gestaltists were interested in processes that cause certain visual elements to seem to be part of the same figure or grouping and certain others to seem to belong to other figures or groups. Their basic observation was that elements or features within a visual pattern do not seem to operate independently. They demonstrated that the organization into figure and ground is in our mind, not in the stimulus.
Neurons in the visual system that are tuned for specific types of contours, edges, angles, and so on. Feature identification involves matching the retinal image to these physiological templates. New templates can be build through learning.
Is the classical template-matching theory.
The perception is not only organized but it renders our interpretation of the stimulus into something that is regular and systematic. Thus perception seems to be trying to make the world simpler and more interpretable.
Gestalt laws of perceptual organization
These laws help us to explain the way in which we organize sounds as well as visual forms or events over time. An attempt to create perceptually the most stable, consistent, and simplest forms and patterns possible within a given visual array.
Law of proximity
States that elements close to one another tend to be perceived as a unit or figure.
Law of similarity
States that similar objects tend to grouped together.
Law of good continuation
States that elements that appear to follow in the same direction tend to be grouped together.
Law of common motion (or fate)
A sort of variant of good continuation and states that elements that move together tend to be grouped together.
Law of closure
States that we tend to ignore gaps between elements in order to form a closed figure. Is a powerful organizer of perception and works in conjunction with other mechanisms.
Law of Pragnanz
States that the organization of the visual array into perceptual objects will always be as good as the prevailing conditions allow. The perceptual systems work to produce a perceptual world that conveys the essence of the world.
Means conveying the essence of something. Allows us perceptually to heal broken patterns, which are actually more common than complete patterns in the visual field.
Meaning they belong to the figure. Shape contours are labled very early in the grouping process. Correct contour labeling can be achieved in a number of ways, including the assignment of contours to different depth planes.
Meaning they are simply a consequence of one object interposed in front of another.
Collections of tiny contour elements or shapes that do not differ in average brightness or color. The orientation of element contours is a much more important aspect of their contribution to texture regions and edges than is the local spatial relation between the contours.
Texture segregation is usually easy and automatic when there are differences in the number, densitiy, or type of few claes or local features that are called texton. Color, brightness, and relative contrast can sometimes overpower shape differences in our perception of textural regions.
Human texture segregation is sensitive to the polarity of the luminance relations between elemtns and the background. Positive polarity refers to an element being brighter than the background.
Refers to an element being darker than the background. Sensitivity to polarity of the contrast between elements and backgrounds indicates that automatic texture segregation is based on some very crude comparisons.
Higher spatial frequency
Like smaller details or shaper contours are more likely to be seen as being figures. Figure perception may be more intimately associated with the parvocelullar than with the low-spatial-resolution magnocellular system.
Is defined in terms of the amount and complexity of information needed to describe a particular stimulus or perceptual organization. Figures with the lowest complexity are apt to be seen as 2D, figures with greater image complexity as 3D. Generally it is the organization with the lowest figural complexity that is most likely to be seen.
Symmetrical figures contain less complexity and are easier to see and to remember. It takes people longer to recognize horizontal symmetry and also longer to detect deviations from horizontal symmetry. Might by evolutionary in nature. Symmetry and regularity not only simplify our perception of the world but they appeal to us at an aesthetic level. The perception of beauty is strongly biased towards more symmetry. Since pregnanz biases us to see all stimulus patterns as more regular and symmetrical, it must then be helping us not only to encode visual patterns more rapidly and efficiently but also to view our friends and lovers as more attractive.
The perception of the actual distance of an object.
Where our bodies are positioned relative to other objects in the external environment.
Estimates of the distance between objects in the einvironment.
Three assumptions (1) All the information we need to see three dimensionally is present in the retinal image or in relationships among parts of the retinal image (2) Visual scene is anaylzed by the brain in terms of whole objects and surfaces rather than in terms of elemantary stimulus attributes (3) The impression of depth or distance arises immediatly in the observer on viewing the stimulus and needs no further computation or any additonal information based on inference or experience.
The desctiption of processes used to create computer programs which will duplicate the visual process.
Modularity of perception
Views the mind as a distinct set of units or modules, each of which is complete in itself and has a specific function with dedicated neural hardware that do a specific bit of processing or computation.
Suggests that perception is like other mental processes in that, in addition to the information available at the moment, we can use infomation based on our previous experience, our expectancies, and so forth. Visual perception goes beyond the infomation given in the visual scene.
Emphasizes the combining of several sources of information to build or assemble our conscious experience of what is out there.
Signals iin the stimulus that we are often not consciously aware of but that function to shape our perceptual responses.
Pictoral depth cues
Your impression of the relative distance in a visual scene is based on a set of cues.
The cues for depth are also available when only one eye is used to view the scene.
Interposition (or occulsion)
A nearer object tends to block the view of a more distant object. It s only a cue for for relative distance.
Means that the missing parts of the figure are perceptually present even though there are no physical stimuli to support that conclusion.
Is the shading that defines the shape of an object. Provides considerable information about the surface shape via pattern of light and dark regions.
Rises from the presence of a second object or surface lying in the path of the light source. Signals shape only through a distorted silhouette of the objects casting the shadows.
In this cue, the image of a very distant object, such as a distant mountain, will be slightly bluer in hue and hazier or less distinct in appearance than the images of nearer objects that are physically the same color.
Relative brightness (or relative contrast)
The light from more distant objects must travel through the atmosphere for a greater distance and may be subject to increased absorption or scattering of the light by the particles in the air. Thus, a more distant object may appear to be less bright.
Retinal image size
The comparison of the sizes of objects in the visual field, relative to each other, is an important part of the process of perceiving relative distance.
In a study, observers tended to judge double-sized playing cards as being much closer to them and half-sized cards as being mich more distant then the normal-sized card. Familar size information are used in conjunction with the changing retinal size to gain the impression of changes in relative distance. As long as the objects are well-known and the distances not too extreme, familiar size can give you absolute depth information, not merely relative depth information.
Parallel lines in the real world, such as railroad tracks, appear to converge, and objects appear to get smaller and smaller in a systematic fashion as their distance increases.
The point where all the perspective lines converge, and objects diminish to invisibility.
The combination of linear perspective and retinal size information into one cue. The gradient (continuous change) is the change in the relative size and compactness of the object elements.
The depth impression associated with texture gradients.
Height in the plane (or relative height)
Refers to where an object is relative to the horizon line. Proximity to the horizon line signals the greater distance.
Structural (or physiological) cues
Arise from muscular responses and adjustments of the eye.
The process that the shape of the lens must change (actually it s amount of curvature changes) in order to keep the retinal image in clear focus. Relaxed accommondation, where the lens is relatively flattened, is necessary if distant objects are to be clearly focused on the retina, whereas a strongly curved lens is needed to image closer objects on the retinal surface. Is a rather slow process and is also limited in the range of observer-to-object distances over which it is useful.
When the eyes move in different directions.
If an object is close to you, you must rotate your eyes inward (toward the nose) in order to focus it s image on the fovea. Convergence and accomondation are weaker depth cues, the eye will use other depth cues preferentially to adjust the eye.
When a target is farther away, the eyes must move away from each other in an outward rotation (toward the temples).
The nearer the object is to the retina, the faster will be it s motion across the retina relative to other objects. Is a good cue for relative distance but not for absolute distance. The accuracy of depth perception depends on the speed with which the head is moving.
Kinetic depth effect (or structure-from-motion)
The fact that motion cues can give us information about the relative depth of parts of an object.
Is the ability to extract depth information from the binocular views. Many people perform in visual tasks up to 30% faster and more accurately when using both eyes.
Each eye has a different view of the objects seen by both eyes and hence a different image of the world. Biocular disparity is the difference between the two eyes' images.
The process by which we merge the disparate images of the two eyes into a single unified percept.
The failure of the two eyes' views to merge completely. Also called double vision.
Crossed VS Uncrossed disparity
Objects more distant than the point of fixation are seen in uncrossed disparity, whereas closer objects are seen with crossed disparity.
An imaginary curved place when we map out all of the points where targets are at about the same convergence or fixation distance in visual space.
The area at which all points in a visual space are fused into single images.
Is a measure of an individual's sensitivity and is based on a comparison to a fixed value for normal or averge. There are large individual differences in stereoscopic depth perception.
An optical instrument which places different stimuli into the two eyes simultaneously. It produces that the disparate images fuse and the objects are seen as if they were an actual 3D scene.
Pictures which sprang into 3D depth when viewed with the eyes converged in front of (crossed disparity) or behind (uncrossed disparity).
If stereopsis is based on the action of disparity-tuned detectors, each of which responds to one disparity value in the arrayy, any dot potentially could be combined with any other dot. Each of the many possible combinations would produce a different depth perception. The task for the visual system is to find the dots in one eye that correspond to the same dots in the other eye. Explanation: Neurons tuned to the same dispartiy cooperate, whereas those tuned to different disparities inhibit each other. Once disparity is detected higher visual centers get involved, with much of the actual depth processing going in V3.
Interaction of depth cues
The accuracy of our perception of depth often depends on the information of several cues. In general, addition of depth cues does increase the accuracy of depth estimtes. Sometimes the addition creates a new emergent depth cue. In many cases, the relative influence of cues will depend on learning and experience. When the cues are in conflict, they can actually result in a reduction in the perception of depth.
Surface deletion & Surface accretion
Can be powerful cues to depth, even when defined only with random-dot displays.
Emerges from a combination of simpler cues. Is a difference in the relative rates of motion with the images in the two eyes. There are neurons in the striate cortex that are sensitive to leftward motion in one eye at the same time that they are sensitive to rightward motion in the other eye.
Subject contours (or illusory contours)
Contours that are not physically present in the retina but are perceptually visible. Any form of occulsion cue, if it is strong enough, can produce a subjective contour. Even infants as young as 8 months see subjective contours. Good evidence that subjective contours depend on our ability to organize the world into surfaces seen at varying distances. Subjective contours may even be processed in the same regions of the brain that process physical contours.
Is the direction relative to our bodies.
Is the object or stimulus relative direction.
It uses as a reference location the midline of the body.
The midline of the head is used as another reference location for right and left.
Is the position in the head that serves as our reference point for the determination of headcentric straight ahead.
Feedback from eye movements could help in determining the visual direction of an object. Both are processed in the parietal lobe. Efference arises from the movement commands sent to the eye muscles.
Arises from feedback from the eye movement itself.
The preferred eye in visual tasks. Sighting dominance is important because the visual direction associated with straight ahead is more strongly influenced by the dominant eye.
Development of space perception
In certain simple animals the perception of direction and distance is inborn. In higher animals, experience may play a larger role.
Tests the depth perception of animals and humans. Some depth perception seems to be independent from experience and inborn. Ultimately experience and innate factors interact to produce an animal's ability to perceice depth.
Refers to the fact that there are particular ages and durations of time when depriving an animal of a particular type of visual experience may produce the largest perceptual deficits. The perception of depth and distance cannot be understand fully unless we assume that some components are explained by inborn factors, whereas others may require active experience to emerge. But even the innate components of perception must mature.
Objects and surfaces in relation to one another. Scenes have intrinstic properties.
The direction and intensity of the light-producing regions in the environment.
Determines the nature of the image through the reflectance of the various objects that come in contact with light.
Is determined with reference to an imaginary line perpendicular to the surface, called the surface normal.
The relationship between the viewer's eye and the scene.
Often occur in situations in which the guess made by the visual system about one of the scene factors is inappropriate.
A smooth variation in the luminance of an image. The visual system tends to interpret shading with the assumption that light shines from above the scene.
Interpretation of a relation between two or more edges as though it will hold for a variety of possible viewpoints.
Assumptions ragarding scene perception
(1) Light shines from above (2) Surfaces are generally convex (3) Objects tend to rest on surfaces (4) Scenes are generally viewed from above (5) Images fare generally generic for a scene
Our perceptions of objects and scenes do not vary nearly as much as the fluctations in the images of those same objects and scenes.
The ability to see an object as being the same size despite changes in objective distance and retinal image size. We estimate distance and size together and adjust our perception of size in accordance with our distance judgement. This has the effect of perceptually enlarging more distant objects. This effect is stronger when more information about distance is avaiable to the observer.
Upper line appears to be longer. Caused by the fact that the two converging lines are automatically and unconsciously interpretated as cues to distance.
Relationship between apparent size and distance
The operation of size constancy enlarges the line that looks like the interior corner of a room because it is judged to be at a relatvively farther distance.
This occurs when the moon on the horizon appears to be larger than the moon when it is high in the sky, despite the fact that it is exactly the same size. When you look toward the horizon, you have a larger number of depth cues for distance, indicating that the moon is farther away than even the most distant point you can see. Our brain seems to assume, in the absensce of any contradictory knowledge, that the distance from us to these objects must not be very great.
Refers to the perception of the enduring shape of an object, despite wide variations in the shape that is projected from that object to our eyes. There is a very close relationship between size constancy and shape constancy because both depend on distance perception for their operation. Even in the absence of prior experience with a shape, we make assumptions about shape orientation.
Box allignment illusion
Edges are seen in this illusion as physically parallel. It depends on the assumptions observers make about linear perspective.
The proportion of light that is reflected from an object's surface, independent of the amount of light that is shining onto the surface.
The amount of light sources in the scene that falls on the object.
It is not the total retinal illumination that matters but rather the ratio of the intensities of the two patches of light on the retina. Might work through the mechanism of lateral inhibition.
One stimulus is chosen as a reference or an anchor and the lightnesses of all other stimuli are judged against that anchor. Commonly the anchor is simply the bringtest or the largest stimulus in the field.
Within limits, we will see a red apple as red whether it is viewed under the white light of the sun, blue light, or yellow light. Is our ability to detect the surface color of an object despite variations in the color of the external illumination falling onto it. The major physiological mechanism involved in color constancy are those associated with adaption processes.
Even though objects are often in motion across our retina, we do not experience them as moving. Instead we interpret this movement as belonging to the head or eyes. Is controlled by feedback mechanisms from our eyes and head movements.
Object position constancy
As I move around an otherwise stationary scene, these relations remein the same despite my ongoing change in viewpoint on the scene.
Egocentric direction constancy
The relative position of objects with respect to me. The head is used as the reference for this.
Covert spatial orienting
The mental process in choosing to view one object and not another. It results in visual benefits for the attended objects.
Overt spatial orienting
Is involved in making eye movements
Is the finding that large changes made to a scene will go unnoticed by an observer unless focused visual attention is devoted to the object undergoing the change.
Figure and Ground
Figure has owership of the edge at an image boundary. Ground is the shape whose visible boundaries are defined by the accident of one object occluding another.
Stimuli that have been carefully constructed to contain different kinds of information at each of several levels.
Global vs Local stimuli
Seeing forest before the trees. Maybe because low spatial frequency information is transmitted through the visual system more rapidly than high spatial frequency information. Low can be carried by the rapid magnocellular stream of processing.
Data driven processing
This type of processing is characterized by a fixed set of rules or procedures that is applied to all incoming data. The visual patterns that are encountered will automatically trigger certain operations.
Conceptually driven processing
In this type, higher-level processes such as memories of past experiences and expectations base on knowledge of the world and previous events or the surrounding context guide an active search for certain patterns in the stimulus input. Both processes must occur for perception to be complete. Only conceptually driven processing would make us see only what we expect du see and we would likely make too many mistakes to survive.
Identification by parts
For example geon theory. For this, an image has to be analyzed in parts and linked to known objects in long term memory. But some objects can be molded mich more readily by geons than other objects.
Identification by views
The descriptions in this model represent views of an object from a particular vantage point and distance. Maybe both are important for identification. By parts for general classes of objects, by views for details.
The meaning of a scene. Provided by the objects that are associated with one another.
Refers to the relative location of the objects and surfaces in the scene. There are specialized brain regions devoted to the representation of the positions of objects in space.
Is rich in meaning but at the same time impoverished in it s retention of specific details incidental to this meaning.
Scene boundary extension
The tendency to fill in a drawing with more detail about the background than was actually there.
Are the basic units of our perceptual experience. Events consist of relations among objects and actions. Similar to sentences or phrases in natural language.
Occur many times in a seccond an cause the retinal image to shimmy from place to place on the retina no matter how hard we tray to hold our eyes completely still. The enr result is that contours in the retinal image are continually moving over a number of different retinal receptors.
Stabilized retinal image
Requires an observer to wear a special contact lens that moves with the eye and has a mirror or a tiny projector mounted. Thus, the image stays on the same retinal receptor no matter how the eye moves.
Our perception of any event does not occur in 'real time', but rather we live in teh past. We refer to an overestimation of the length of a stimulus as visible persistence. The duration of it depends on the adaptive state of the eye.
Meaning that two stimuli appear to form a single unified stimulus. The longer the time interval, the less the stimuli unify. In a study, harder to see a missing dot when the time interval increases from 0 to 100ms.
Means that a stimulus that occured later in time interferes with the processing of an earlier stimulus.
This pattern of accuracy is sho for a first shape and is taken as evidence that there is a perceptual competition when two objects are flashed in quick succession. It is the temporally later shape that wins the competition for accuracy.
The spotlight of attention. It is limited in the amount of detail it can register at once.
Critical fusion frequency (CFF)
Measures the temporal resolution. When observers are asked to discriminate a light that is flickering between on and off, the CFF can fall anywhere between 10 and 60 cycles per second. This varies so much because it is sensitive to a number of variables.
"The rapid ""where"" stream, which is a magnocellular-dorsal system. Most important time keeper for vision and we are lesse aware of it compared to the other stream."
"The slower ""what"" stream, is a parvocellular system."
Active neurons have a tendency to cause other neurons with which they are connected to fire precisely the same temporal pattern on a millisecond scale. This is thought to form the basis of consciousness!
An attempt by higher brain processes to compensate for the task-specific deficiencies of lower visual processes. Refers to the trail of visible persistence that is left by an object in motion. Contributes to difficulty in seeing the precise shape of an object in motion, although it may assist in determining it s trajectory.
Suppression of motion smear
Motion smear is suppressed when an object in motion follows a predictable path. This is conveyed by the magno pathway inhibiting the parvo stream.
The likelihood that you see a target is greatly reduced if the stimulus is presented when there is another target nearby in both location and time.
When two targets are present, the first interferes with the perception of the second. The weakest masking form.
Perception is impaired by the presence of an extraneous stimulus presented at the same time.
In this, the target and the mask are presented to only one eye.
In this, the target is presented to one eye and the masking stimulus to the other. Shows an U-shaped masking function. Strongest for masking at 100ms.
Based on the assumption that it takes a certain amount of time for a target to be processed well enough so that we can recognize it. Then masking appears because the processing of the first target is not completed befor a second pattern (the mask) appears in the same spatial location.
Auditory continuity illusion
Is the perception that a tone continues through noise (even though it is not physically present).
Phonemic restoration effect
In this, the auditory system of the listener supplies missing parts of speech when the stream of speech is interrupted by other sounds. The missing information is determined from the meaningful content. Occurs also in vision. The percepual system is filling in to effectively heal stimuli and make them perceptually whole in order to correct of distortions or gaps.
"Is the few seconds of our current experience of ongoing consciousness
In this, many philosophers state, occurs our immediate experiences.
Involves different measurable aspects of experience.
One of the most common judgements that we make about time flow.
Order (or sequence)
Involves the determination of which event came first, second, and so forth.
Events occured either after each other or simultaneuously.
Planning of an ordered sequence
Anticipation bevore an event actually occured.
Assumes that there is some physiological mechanism that we can use as timer for our perception of time. Idea: Flow of subjective time is related to some body mechanism that acts in a periodic manner with each period serving as one 'tick' of the biological timer. There are propably several biological clocks in animals. 30ms seems to be the smallest time difference that can be discriminated by humans. These 30ms may form the smallest perceptual unit because it is the most irreducible unit of neural communication.
In this, time is derived via some cognitive process that is based on things like how much sensory information is processed.
Varies with a cycle of roughly 24 hours. Can be demonstrated experimentally in the absence of light or temperature changes. Most of us will start to begin a day in these experiments that is approximately 25 hours long.
Refers to the synchronization between the biological clock and the local day-night cycle. Body time does eventually adapt to a new time zone at a rate of 1/2 to 1 hour per day.
Light is the primary zeitgeber. Light can reset the biological clocks of animals reared in the dark.
Suprachiasmic nucleus (SCN)
The SCN contains only a few thousand cells. However, it has large effects on our timing behavior. SCN receives input from the visual system.
It is normally secreted at night and appears to reset the circadian clock of the SCN. The internal circadian timer of blind people is not normal.
Are variations in a stimulus that occur so quickely that there is no corresponding change in the perception.
Each moment of exerperience is about 100ms in duration, which would be the shortest perceived duration a stimulus can have. In one study, the minimum duration of a stimulus in consciousness was around 60 to 70 ms. The minimal resolvable time varies with age, drug intake and the distribution of attention.
When there is a biological pacemaker, it makes sense that it would speed up or down with other physiolgical processes in the body. At higher body temperature the speed of physiological activities increases, and this causes the pacemaker to tick more rapidly. Physical time seems to pass more slowly and duration estimates become longer in hyperactive children.
The ticking rate of the cognitive clock depends on this. The greater the number of events, or the more changes that occur, during an interval, the faster your cognitive clock ticks and thus the longer is your estimate of the amount of time that has passed.
Filled duration illusion
Refers to the fact that a duration filled with stimulus events is perceived as longer than an identical time period empty of any external events.
Processing effort model
An increase in the amount of information processing required during an interval leads to an increase in the estimated duration of the interval.
Storage size model
The more items you store in memory, during an interval of time, the longer you judge the time to be.
Temporal processing model
The more attention you pay to the passage of time, the longer the time interval appears to be. Anything that draws our attention away from actually monitoring the passage of time should shorten our sense of time passing. Also, as people age, the passage of larger units of time seems to be much faster. The total amount of time that older people have experiences serves as a reference level and the perceived duration of any time interval is compared to this baseline.
There are single neurons that are sensitive to the presence of motion in a particular direction and at a particular velocity in their receptive field. Many motion specific cells are found in V5, the medial temporal part of the brain.
Suggests that there are neurons that become fatigued after repeated exposure to the same movement. This bias the system in favor of seeing motion in a direction opposite to that of the original stimulus.
It involves exposing the eye to a moving pattern such as a field of stripes. Prolonged viewing of such a stimulus temporarily reduces an observer's ability to detect motion in the same direction as the stripes. Consistent with the idea that our brains contain movement-sensitive celles that are tuned to a particular direction and speed.
The apparence of motion can be archieved by the sucessive presentation of two stationary images. Used in the cinema. The medial temporal cortex is actively involved in 'constructing' the apparent motion out of the nonmoving input displays.
Model for the arrangement of movement neurons. In this model, simple cortical cells with their receptive fields fire and will be compared by a comparator cell to produce the output. The older tectopulvinar pathway is more involved in motion perception than the newe geniculostriate pathway. Especially the magnocellular system is most responsive to movements.
With this technique, the importance of the magnocellular system in motion perception can be shown. It shows that the magnocelluar system responds better to luminance differences than the parvocellular system.
Is the correlation between the movements of dots in successive frames. Humans are very sensitive to small correlations in these displays. Changes are recognized that involves only 5% of the dots.
The system that responds to image changes.
The system that interprets motion from our eye and head movements.
The only information is the movement of the target relative to the observer's position in space.
Is the movement of target relative to other objects. Humans are much more sensitive to these changes.
Motion correspondance problem
How do we correlate motion to different objects? For that we have a preference for proximity in space and in time
Because individual motion sensors consider only a small region of any given image, information from the local signals must be integrated by the visual system in order to determine the global direction of an object in motion.
Refers to a perceived motion that is caused by real motion of the sourrounding context. Used in the cinema
Stimulus onset asynchrony (SOA)
Refers to the time that elapses between the onset of one frame and the onset of the next frame in apparent motion.
Motion sequences shown on TV and cinma, where each successive frame lasts only a few ms and the spatial displacements of an object from frame to frame are only a few minutes of arc. Govered by primitive and preattentive short-range processes. Activates Reichardt-type sensors, with small time and space parameters, that take only luminance changes as input.
Apparent motion of only one or two objects over much larger spatial displacements with longer temporal intervals. Higher level cognitive processing mechanisms play a role in this motion detection. The long-range motion displays activate sensor cells with larger spatio-temporal windows that are stimulated by luminance, color, texture, and even motion.
Random-dot kinematogram (RDK)
Refers to random-dot displays used to create motion sequences.
Structure from motion
Relative motion information alone is sufficient to enable the processes responsible for shape perception to operate. It is V5 that seems to be implicated in the brain, specifically the dorsal section of the medial superior temporal cortex.
Ability to identify other humans and their activities solely from the patterns of motion made by their trunk and limbs. Infants as young as 4 months seem to notive that biological motion is different from other forms of motion. Under some circumstances, some objects can only be identified by their unique pattern of motion.
Time to collision
Refers to judgements about whether and when two objects will collide
Refers to calculations of an object's time to collision obtained from the ratio of the object's size on the retina to the rate of cange in it s retinal size over time.
Linear optical trajectory
Means in practice that baseballer run so as to maintain the path of the ball on their retina in as straight a line as possible.
Eye-head motion system
Operates largely without our awareness.
Smooth pursuit movement
Following the path of a physically moving object. It is designed to keep the image of the target on the fovea, which is the part of the retina that can register the greatest detail.
Voluntar pursuit movement
Allows us to keep a moving object at the center of our gaze.
Reflex pursuit movement
Keeps images of objects relatively fixed in one place on your retina despite the fact that your head may be moving. Only found in animals that have foveas.
Underestimation of speed and distance when a target moves
We see the world as stationary although we are moving.
Objects seem to maintain a fixed position relative to us, despite the rotations of both our head and eyes.
Proprioceptive (or eye position information)
Motion is detected via feedback information from the six extraocular muscles that control the eye movements. It enables the visual system to monitor eye position.
In this theory, the information is flowing in from the eye muscles to the brain that is the crucial message for the interpretation of movement.
In this theory, the interpretation of the origin of movement is based on information from the message sent out from the brain that initiates an eye movement. Based on Helmholtz. Many researchers believe that both theories are needed to provide a full explanation of the eye-head movement system.
Sitting in a train, seeing movement, believing the self is moving, but the train next du you is moving. Is important because it reveals the interplay between the visual and vestibular systems in the perception of body motion.
Our perception of self-motion depends on an analysis of the continually changing aspects of the retinal image as we move. There seems to be a complex interaction between the visual and the nonvisual inputs to give us a feeling of self-motion. The right hemisphere might be more important than the left for self-motion perception.
As we move forward, the visual array in front of us is a radially expanding pattern in the center of our visual field and a laterally translating pattern in our periphery.
Focus of expansion
Is the center of the outward flow in self movement. It indicates the direction of your movement. Stimulation of the peripheral visual field is necessary to induce the feeling of self-motion.
Informs us about the position of our body in space using evolutionary old mechanical mechanisms. Takes place outside of consciousness. Motion sickness is often caused by a mismatch between visual and vestibular or kinesthetic inputs.
Contains the structures for the vestibular systems.
Most of the fibers leaving the vestibular nuclei are motor or efferent fibers.
A process by which several inputs combine to produce a single coherent perception.
The various ways by which we select among all that is there to be looked at, listened to, felt, smelled, or tasted are grouped as attention.
Means that attention is drawn or pulled to a source of sudden change in your sensory world.
Filtering out the other events, attending to only one of the serveral available distinct and separable sources of information about the world.
The distingt and separable sources of information about the world.
Searching for a relevant stimulus in the environment, scanning your sensory world for particular features or combinations of features.
You are expecting something to happen and in preparing for that event you momentarily attended to 'empty space' until it happend. Our expectations interact with how we direct our attention. Cues caused enhanced activity in frontal, parietal and temporal lobes, indicating that these areas are part of a network involved in decoding the cue and directing voluntary attention to an expected target location.
Paying attention to a single target or event.
"Dividing attention among several targets or events. Very difficult but under some conitions possible without depressing performance
Responses such as flicking the eye in the direction of a sound or peripheral movement occur autmatically. The most effective orienting stimuli are loud sounds, suddenly appearing bright lights, changes in contours, or movements in the peripheral visual field.
Seen attional orienting.
Unseen attentional orienting.
Refers to the fact that visual stimuli seem to be more capable of drawing our attention to particular locations in space than auditory stimuli.
A special abrupt-onset stimulus. Faciliate responses to targets near the cue for about 100 to 200ms.
Information in advance about where or when something is likely to happen.
We imagine that our attention can gaze about indepently of where our eyes are looking. Attention seems to jump from point A to point B like a saccade. Three aspects 1) Locus 2) Extent 3) Detail set
Is the region of the stimulus field, in which the occurance of a stimulus can produce responses from that neuron. The thalamus and the superior colliculus are involved in orienting visual attention. The parietal lobe is also an important brain area for especially the covert attentional gaze
Posterior parietal lobe
Important for directing the covert attentional gaze, also involved in overt orienting.
Damage to the posterior parietal lobe results in this condition, which is the inability to pay attention to and to notice stimuli from one half of the visual field.
The direction of the sound emanating directly from the sound source takes precedence over other sounds in localization
The difficulty of shadowing depends on the nature of the message. Meanning and grammatical structure help us to attend to one message and filter out others. Shadowing is also easier of the messages come from two different places in space, are different in pitch, or are presented at different speeds. However, listeners can remeber very little of the rejected message in the shadowing task. It seems that material in the unshadowed ear is available for processing, and attention, for a short while after it occurs, but unles it is attended to it is not entered into long-lasting memory.
Our lack of consciousness for stimuli that we are not paying attention to.
The video overlap phenomenon
Like auditory filtering, visual filtering allowes little of the filtered-out information to make a lasting impressing.
Chages in visual stimuli are often not registered. Much of our visual experience is not as solid and complete as it seems. Rather, attention acts to solidify only part of a rather volitate and dynamic represenation of the world and only as long as that part is attended.
In this area, the behavior or single neurons is affected by attention. Evidence suggest that the pulvinar nucleus of the thalamus assists in attentional filtering by selectively enhancing activity in sensory cortical areas such as the temporal lobe.
Extensive pratctice can make a skill autmatic, then it requires less attention, allowing more attention to be allocated to another less-automatic skill.
Requires a lot of attention.
Our eyes are constantly exploring the visual field with high-speed ballistic movements. The movements of the eyes are guided by our itentions, our previous experience, and by the way the eye system works.
Inhibition of return (IOR)
Refers to a decreased likelihood that people will move their eyes and their attentional gaze back to a location they have recently looked at. It either arises from a bias against returing attention to a previously attended location or object because the information has already been extracted from it, from a sensory refractoriness at the previously stimulated site, or arises from various motor inhibitions.
A search when the search target differs from all distrecters by possessing a feature they dont have. Also called 'pop-out search'. The search time is independet from the number of distracting items. Search is accomplished in parallel.
A search when the only way to detect the target is to detect a conjunction of features. Much harder than features searches. The number of distrecters affect the search time, called 'searial search'
Feature integration theory
Asserts that attention must be moved sequentially from place to place in a conjunction search or in any other difficult search, but that this is not necessary in a feature search, where the relevant features pops out from the display.
The relatively variable features of a scene, such as the shapes and colors that change with viewpoint and lighting.
Such as the relative orientation of an object and surface curvature, tend to remain constant over changes in the observer's viewpoint and scene lighting.
Extinct some distrecters from the search, for example treating them as ground. Is apparently mediated by the left hemisphere of the brain. After training, conjunction search can become independelty from the number of distracters!
After a while, an observer becomes less sensitive to stimuli changes, or he becomes less willing to report the change.
Relationship between performance and arousal. Overall performance of any task peaks at an intermediate level of arousal. This level is lower for difficult tasks than for easy tasks. Suggests that very difficualt tasks are best performed under low levels of arousal.
Imply that perceptual attention is structrually limited. The notion was that there is a bottleneck or a filter somewhere in the information-processing system.
Early selection model
According to this model, you ould isolate stimuli by means of physical characteristics rather than by meaning. Filtering occurs very early in the process.
Late selection model
They hypothesize that all information entering sensory systems gets some preliminary analysis.
If there is more demand than ressources available, then performance suffers. The first theories saw attention as a 'limited pool' of capacity.
"What you perceive at any moment of time is simply what is present in your consciousness
Refers to factors involving perceptual stimuli that are unconscious at this moment but can easily be brought into consciousness.
Illusion of complete perception
We feel that we are aware of everything about the current scene.
Particular kind of consciousness. When we are perceptually aware of something, we can report it's presence, either verbally or by some signal.
Philosophical postion that states that whatever consciousness is, it is a phenomenon of the world just like any other. Adopted by scientists.
One group of monits who believe that the material world is fundamental and that consciousness is simply another phenomenon of matter.
Other group of monits who believe that consciousness is fundamental and that the physical world as we know it arises from consciousness itself.
Position that consciousness is a phenomenon of the mental world or even possibly of the spiritual world. Place consciousness outside of the realm that can be studied by science.
Idea that consciousness is made up of mental stuff that is different from the physical stuff that makes up the world.
Idea that although everything that exists is made up of physical matter, some of that matter is arrenged in ways that give it special, nonphysical properties.
Stream of consciousness
The perceptions and thoughts seem to be always changing and yet there is never any dead time in them, any time when nothing was happing consciously
Intervals of time when our consciousness is occupied with a particular perceptual object or thought. Like studying a face to find out whether you know the person.
Times when we are aware of relationships between thoughts but of no particular thought. This is like a straight run of current in the stream from one place to the other.
Refers to the availability of mental contents for verbal reports and other actions.
Refers to the actual experience of stimuli such as the color red.
Refers to thoughts about one's own experiences.
Refers to awareness of a 'self' that is disting from the rest of the world.
The view from each eye is slightly different. The two eyes seem to fight for control of consciousness. First the view of one eye is dominant and visible in consciousness, thatn the view will switch. Rivalry because the two eyes' views are competiong with each other to gain control of what a person is seeing. Each set of neurons in the eyes tries to suppress the set of neurons representing the other eye's view by sending inhibition to them.
Represenation rivalry (or pattern rivalry)
Alternative theory to binocular rivalry. Although our experience is of an alternation between eyes, it is really an alternation between stimulus configurations. Higher-level neurons are registering a pattern, regardless of the eye used to receive them. May be responsible for flucations in consciousness that have nothing to do with binocular discrepany of inputs (many ambigious figures). It seems likely that both forms of rivalry appears depends on the nature of the stimulus.
Information from an unseen prime stimulus makes it way to the brain and influences the individuals behavior.
If a stimulus is presented at the same time as another stimulus is in the right visual field, the left stimulus can no longer be perceived. If consciousness has reached a reasonable conclusion as to what the stimulus represents, then no further investigation is needed. However, with a clue that an alternative exists, attention will begin to redistribute over the stimuls and noew details can come to consciousness.
Smooth tracking movements
You need to be continously conscious of a target at all times or else it will drift into the periphery.
When we follow a movement, our consciousness of our own eyes turns off during the actual movement period.
Stable world assumption
Assumes that most things in the world around us are standing still and do not have to be continously monitored. This saves a lot of mental processing capacity that can be put to use interpretating the nature and identity of objects that we are looking at.
Sighting dominant eye
Refers to the eye, which information comes to consciousness while the nondominant eye's view is rendered unconscious however, it is always available at some level. Because of that, we don't see double images. In 70% of the population, the right eye is dominant. Identifying and lovalizing targets are seperate functions with different representations in consciousness. Grasping occured some ms before recognizing in one study.
People with this condition seem to be conscious of some aspects of the sensory world but often unaware to others. They tend to break apart items that appear to be inseperable in consciousness like shape and orientation.
If a subject with this condition is shown a series of overlapping items, he might report a single item and deny that he can see any of the others. It seems to be impossible to meld different parts of an object into an integrated and unified figure in their consciousness.
Visual integrative agnosia
Combination of visual agnosia and simultagnosia.
A condition in which a person can act appropriated toward visual objects even in the absence of perceptual awareness of important aspects of those objects or even of their existence. A blind person who can grasp for an object.
Lesions in V1 results in localized blind regions in the visual field corresponding to the location of the damage. If a stimulus falls in the region of a scotoma, the patient cannot report even the existence of the relevent visual stimulus in consciousness.
Dorsal processing stream
The visual action system. Is older in evolutionary sense and we share it with all animals that have to use vision to guide action. This system is fast and seems to have direct connections to the brain centers that initiate body and eye movements. Does not need perceptual awareness to operate efficiently. Much of the information that this system uses so quickly and efficiently can also be passed on the vental perception system where it could be made available for futher processing in consciousness.
Ventral processing stream
The vision perception stream. Is newer and seems to have been added to the larger human brain. This is the system that seems to construct our perceptual consciousness. Slower system that needs perceptual awareness.
Refers to the fact that movements can be monitored and corrected while they are being executed. Assits the accuracy of the action system.
Neural correlates of consciouness
Refers to neural activity, perhaps in a specific brain area, which was closely associated with conscious awareness. To have consciousness of the visual stimuli requires dorsal stream activation. The correlates of consciousness invovle many centers in the brain.
Consciousness seems to require the passing back and forth of a lot of neural information. A feedward sweep from the retina upwards which is the analysis pathway.
In which cortical areas that receive input from other areas send feedback to the orignitating area via so called downward projections. This reentrant input then modifies the output of that area.
"Perhaps the true function of consciousness is to combine all of the information from the various sensory streams and various locations in the brain, to resolve the conflicts that might arise between the individual processes, and to form a global hypothesis as to what the objects and relationships among obects are, out there in the world. Consciousness is the ""glue"" that holds togehter the individual qualatative sensory ""atoms"" that make up our perceptual universe."
Synchronous neuronal firing
Used to bind the processing occuring in a number of discrete brain regions to create the larger functional unit that we are aware of in consciousness. Part of the 'glue' that binds all of this activity together is timing. It seems to be strongly associated with perceptual and other forms of awareness.
Perceptual objects represented by neurons that are part of the dynamic core at any moment are in consciousness, whereas those represented by neurons not in the dynamic core are not in consciousness.
Life span developmental approach
Assumes that knowledge of a person's chronological age will allow us to predict many aspects of perceptual behavior. A long-term approach.
Perceptual learing approach
A short term approach. Views the changes that occur in perceptual responses as a result of a circumscribed set of experiences.
Loss of connections between neurons during childhood. Changes in brain during materurity are due to a relative increase in the white matter in the brain, which reflects myelinization of neurons.
Involves eye movements, head turns, and visual following behavior in response to a stimulus that appears suddenly or is moving.
If an infant is looking at one target longer than at a second, this is taken as indicationg preferences for that target. Implies that the child can discriminate between the patterns.
Forced-choice preferential looking
Allows the study of stimulus detection as well as discrimination. The idea is that if the baby respondes differently enough to different stimuli so that observers looking at it can discriminate these differences, then the baby must be discriminating between the stimuli.
Refers to the fact that at first a baby will spend a good deal of time looking at a novel stimulus, but as time passes it will begin to look at it less and less.
Is the renewed interest in the stimulus.
The infant needs to be aroused enough to process stimuli. Part of visual attention of the child.
It usually invoves turning the eyes and perhaps the head or body in the direction of the stimulus. Infants eye movements are differently than adults. Infants are much slower to begin a saccade and tend to make a series of small saccades, often not reaching the target for well over a second. Smooth pursuit eye movments are possible but not efficient and the child only manages to hold the target stimulus on its fovea for about a third of the time.
Refers to a repetitive eye movement sequence in the presence of a moving pattern.
Patients have difficualty perceiving and identifying human faces. Young infants have a preference for face like stimuli. In that, faces seem to be very spacial stimuli, they are recognized very early.
High-pitched speaking voice towards a baby. Infants of 4 to 6 monts of age respond to such talk by increasing their smiling and vocalization.
Useful field of view (UFOV)
The area of the visual field that is functional for an observer at a given time and for a given task.
Slight hearing handicap
Loss of sensitivity of 25dB. Problems with faint speech.
Marked hearing handicap
Hearing loss at 55dB. Individuals have difficualty understanding loud speech. Corresponds to a 45% hearing loss of speech range sounds.
Aging of the brain
Decrease in white matter. General slowing of neural responses, accompanied by an increasing persitance of the stimulus in the nural represenation. Less control over the information, that enters and is sustained in working memory.
Strongest form of interaction between experience and development. Presence of some sort of relevant experience actually determines both the presence and final level of the ability.
Weakest form of interaction. Represents no interaction at all, and the ability might be expected to develop regardless of the individual's experience or lack of it.
Final level of ability, which is already present or developing, is improved because of experience.
Increases the rat at which an ability develops but not ist final level.
Serves to stabilize or to keep an ability that is already present.
Our perceptual mechanisms adapt to the tasks and environments that they are presented with by increasing the amount of attention they pay to important stimulus dimensions and features.
Refers to a single stimulus element. E.g.: Green or 2 cm
Refers to a variable aspect of the stimulus. E.g.: Color or lenght
"Refers to the fact that stimuli, which were once seen as being the same through experience become distinguishable. Seems to be the reason that you can identify faces of your own ""race"" more easily."
"Reverse of differentiation. Involves treating a complex stimuli configuration as a single functional unit in consciousness. Example: Chess experts see patterns on the board. Problem: It is more difficult to recognize a picture upside down
A stimulus shapes the response of a receptor. Involves an actual change in the nural receptors that comes about through interaction with the environment. Comes about simpley because the stimulus is processed many times and has behavioral significance.
Deprive a subject from the oppurtunity to use a sensory modality. Prevents any perceptual learning from occuring stimulus imprinting. When the subject has fully matured and the modality is poolry developved, experience is needed for the function.
Used to selectively bias, rather than eliminate certain perceptual abilities to test whether experience plays a role in the development of the modality.
Refers to a particular time period during which an experience is most required and most effective. May correspong to periods of maximal growth and development in the nervous sstem.
Describes what happens in the nervous system after exposure to restrictive rearing. It drastically alters the response characteristics of nerurons in the brain. Example: Dark reared animals are less responsive to visual information and use it less efficiently in other tasks.
Refers to the region of the outside world to which an eye will respond, measured in degrees around the head.
Quality of the human visual system, means that it often reacts differently to stimuli depending on their orientation. In general, the human visual system shows a slight preferencefpr horizontal stimuli.
The resolution acuity and vernier acuity are poorer for stimuli oriented diagonally. Horizontal and vertiacal lines can be better detected compated to diagonally lines.
Stimulation that acts on a passive observer. It seems that normal perceptual development depends on active bodily movement under visual guidance.
Stimulation that changes as a result of an individual's own movements. Necessary for the development of accurate visually guided spatial behavior.
Researchers used distorting lenses to rearrenge the spatial relations in the world. Takes some time but real perceptual changes occur. Easier to adapt when input was faciliated by the notion of gravitational directions along with interaction with familiar objects. Better adaptiation with some sort of feedback about the errors.
After the use if distorting lenses, an observer err int he direction opposite to that of the inital distortion. Evidence that some perceptual changes occured
Decrease in the strenght of illusions. Implies that perceptual learing is taking place. Information from eye movements is used to reduce a perceptual error. The perceiver of the illusion does not know that the perception is in error, nor that illusory error has been reduced as a result of his active interactions with the illusion figure! No change in the oberserver's own awareness!
A decision making process in which we deduce, on the basis of all available information, what the stimulus object is.
Perception is not an automatic process of registering stimuli but rather one that requires extensive computation and intelligence to succeed.
Stimuli that are present in our conscious experience.
When we look at a photograph and are later asked to recall or to draw what we saw, we tend to remember seeing information that was not really in the picture but was likely to have existed just outside the camer's field of view.
Carpentered world hypothesis
Because of the urban environment we live in, we may learn to depend more heavily on depth cues based on linear perspective than woul people who lives in less carpentered and more rural environments. People in more carpentered environents are more fouled by the M�ller-Lyer illusion.
Refers specifically to the experience or predispositions an observer brings to the perceptual situation.
Meaning of experience for perception
Much of what you perceive is determined, not just by the stimuli that are out there in the environment, but by what your experience, culture, and education have set you to perceive.