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Vision
- - our eyes can only respond to visible light waves a band called the visible spectrum
- - shortest-violet longest- red
- - ROY G BIV
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The Eye
- - about 1 inch in diameter
- - cornea- transparent, protective cover
- - bends light rays inward, directing i through the pupil
- - the iris dilates & contracts the pupil to regulate the amount of light entering the eye
- - just behind the iris & the pupil is the lens
- - composed of many thick layers, it looks like a transparent disc
- - the lens focuses on viewed objects
- - it flattens as it focuses on close objects (AKA accomadation)
- - by about age 40, the lens loses its ability to change its shape to accomodate for near vision (AKA presbyopia) "old eyes"
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From Lens to Retina
- - the lens focuses objects on the retina
- - projected upside down & reversed left to right
- - the image (from lens to retina) can be projected too short or long
- - nearsightedness (myopia)- when the lens focuses images of distant objects in front of rather than on the retina. near objects are clear, but far ones are blurry
- - farsightedness (hyperopia)- occurs when the lens focuses objects behind, rather than on the retina. far objects are clear, but close objects are blurry.
- - at the center of the retina is the fovea
- - about the size of a (.)
- - images are focused on the center of your fovea. it has no rods but about 30,000 cones packed tightly together. it provides the clearest sharpest vision in the whole retina
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The Rods & Cones
- - located at the back of the retina
- - light sensitive 120 million rods, 6 million cones in each retina
- - the cones allow us to see color & fine detail in adequate light. they dont function well in dim light
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From Retina to the Brain
- - rods & cones transduce or change light waves to neural impulses
- - about 1 million axons lead from the wall of the retina to the brain
- - there are no rods & cones where the cable runs through the retinal wall (AKA blind spot)
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Vision and the Brain
- - beyond the retinal wall is the optic nerve
- - the two optic nerves come together (AKA optic chiasm)
- - this plays a role in depth perception
- - from the optic chiasm, the optic nerve fibers extend to the thalamus & transmit impulses to the primary visual cortex
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The Primary Visual Cortex
- - part of the brain where visual information is processed
- - through research we have discovered that feature detectors (coded at birth)
- - these are some neurons that respond to certain patterns. some respond to only lines & angles, while others respond to vertical or horizontal lines.
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The Primary Cortex
- however, we see the whole images because the primary visual cortex takes these pieces, combines them into & assembles them whole visual images
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Color Vision
- - 3 dimensions of light combine to provide us with color
- - they are: hue ( the specific color perceived), saturation (the purity of color), & brightness (the intensity of the light energy)
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Theories of Color Vision
- - trichromatic theory- thomas young (1802)
- - there are 3 kinds of cones in the retina that respond (sensitive to) to blue, green, & red)
- - opponent-process theory- Ewald Hering in 1878
- - 3 kinds of cells respond by increasing or decreasing their rate of firing when different colors are present. Red/green, yellow/blue, & white
- - afterimage- stare at a color & then stare at a white object. the negative will remain. both theories are correct in a way.
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Color Blindness
- - the inability to distinguish certain colors from one another
- - about 7 % of males & > 1% of femals suffer from color blindness
- - a person can have degrees of CB
- - people with normal color vision, the X chromosome may have as amny as 9 genes for color perception. others may have as few as 2.
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The Absolute & Difference Thresholds
- - absolute threshold- the difference between not being able to perceive something & just barely able to perceive it
- - the minimum is 50% of the time
- - the difference threshold is the measure of the smallest increase or decrease in the physical stimulus that is required to produce the JND
- - Ernst Weber- stated that the JND depended on a % of change in a stimulus rather that a fixed amount
- - the threshold is different for the senses
- - a 20% difference is needed for taste
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Transduction & Adaption
- - we do not actually see with our eyes or hear wiht our ears. these sense organs are only the beginning. sensations are completed in the brain.
- - to get the "messages" to your brain, your sense organs have highly specialized cells called sensory receptors. they respond to light, odor, etc.
- - the process of converting sensory information into neural impulses
- - we experience a sensation only when the appropriate part of the brain is stimulated
- - over time, we "get used to" certain levels of stimuli (AKA sensory adaptation)
- - SA allows us to shift attention to stronger stimuli
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The Mechanics of Smell
- - the human olfactory system can distinguish between 10,000 different smells
- - you cant smell a substance unless some of its molecules vaporize
- - olfactory epithelium- (2) 1 in. patches of tissue at the top of each nasal cavity
- - contains 10 million neurons
- - the intesnity of the smell stimulus depends on how many olfactory neurons are firing at the same time
- - dogs have about 20 times more than the amount of olfactory receptors that humans do
- - olfactory neurons are different from other neurons. they both come into direct contact with sensory stimuli & reach directly into the brain.
- - they function for about 60 days, die & are replaced by new cells
- - olfactory neurons fire a smell message directly to the olfactory bulb (just above the nasal cavities)
- - signal is sent to the thalamus & orbitofrontal cortex & then sent to other parts of the brain
- - the process of sensing odors is the same in every individual, but some are more sensitive to smell than others
- - young people are more sensitive then older people
- - nonsmokers are more sensitive than smokers
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Smell & Memory
- - smell can trigger emotions
- - the olfactory system sends info to the limbic system (an area of the brain that contains emotions & memories), but bypasses the hippocampus (involved in most of our memories)
- - in older people, the greater loss of olfaction, the greater chance of dimentia
- - preventing a loss of smell will not prevent dementia
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Pheromones
- - most animals excrete pheromones- to mark territory or to signal sexual receptivity
- - humans produce androsterone- it can affect heart rate & mood.
- - research has shown that humans, although not consciously aware of it, respond to pheromones when it comes to mating
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Touch
- - your skin is your largest organ
- - tactile info is sent to your brain when an object touches or depresses the skin
- - touch receptors are sent through the skin to the spinal cord reaching the somasensory cortex
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Pain
- - 1. motivates us to tend to injuries
- 2. restrict activities
- 3. seek medical help
- 4. teaches us to avoid pain-producing situations
- - chronic pain- lasting 3 months or more is felt by 34 million americans
- - 3 most common types:
- - low back pain, headache, & arthritis pain
- - gate-control theory- an area in the spinal cord that acts like a "gate." it can block or send pain messages to the brain
- - you feel pain only when pain messages are carried by slow-conducting nerve fibers thus causing the "gate" to open.
- - it also blocks large, fast-conducting nerve fibers that can block nerve fibers
- - when you are hurt, your often rub/apply gentle pressure to the area, thus stimulating large, fast-conducting nerve fibers & blocking some slow-conducting nerve fibers
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Psychological & Cultural Influences on the Experience of Pain
- - pain has both physical & emotional components & can vary from person to person
- - people feel the most pain when they have negative thoughts about it, fear its potential threat to their wellbeing & express feelings of helplessness
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Endorphins
- - americans spend more money on pain relief than on any other medical purpose
- - over $40 billion a year
- - endorphins are released naturally ( which block pain) when you are injured, experience stress, or extreme pain, laugh, cry, or exercise
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Prior Knowledge
- - the knowledge we possess about a given sensory stimulus influences how we perceive it
- - prior knowledge can sometimes enhance perception, but it can lead to errors as well
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Bottom-Up & Top-Down Processing
- - bottom-up processing- taking prior knowledge & using it to make sense of something new/unknown. In other words, taking individual parts & finding patterns to make sense of the information
- - top-down proceesing- previous experience & perceptual knowledge are applied to recognize the nature of a "whole" & then logically deduce the individual components of that whole
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Perceptual Set
- what we expect to perceive determines, to a large extent, what we actually see, hear, feel, taste, & smell. these are based on prior knowledge
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Attention
- - inattention blindness- its hard for our eyes to keep track of many moving objects at the same time
- - even though we see changes, we do not always perceive them
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Social Perception
- - research indicates that when judging motion based on conflicting auditory & visual input, people rely on auditory input.
- - in the case of social perception, the opposite is true. visual clues often take priority over auditory cues.
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