perception test 2

image on the retina can be caused by an infinite number of objects

inverse projection problem

people recognize objects that are not in sharp focus

human have the ability to recognize objects from different viewpoints

perceptions are created by combining elements called sensations

the dots on the face are combined to form a face

• illusory contours
• represent edges of a cube there doesnt really exist

• whole differs from the sum of its parts
• perceptual organization

how small elements are grouped into larger objects by our brain

1. law of simplicity/good figure/pragnanz: stimulus is perceived in such a way that the resulting figure is as simple as possible

2. law of similarity: similar things appear to be grouped together

3. law of good continuation: point that results in smoothly curving lines are seem as belonging together and the lines appear to curve in such a way that they follow the smoothest curving path.

4. law of proximity/nearness: things that are nearer appear to be grouped together

5.law of common fate: things that are moving in the same direction appear to be grouped together.

6. law of meaningfulness/familiarity: things that appear meaningful are grouped together


7. Law of common region: things that are within the same region appear to be grouped together

8. Law of uniform connectedness: elements that are connected by properties such as lightness, color, texture, are grouped together.

9. Law of synchrony: visual events that happen at the same time will be perceived as belonging together

how elements are seperated from the rest of the scene

when a seperate object usually seen as the figure stands out from its background which is the ground.

figures in the lower part of a display

for left-right displays, small preferences for left region

• neurons fire
• neurons hardly fire

neurons have very small receptive fields, they tend to look at only a small portion of the stimulus field

neurons still fire in response to figure-ground seperations

neurons receive signals from higher areas of the visual cortex based on context and experience

people are sensitive to vertical and horizontal lines than to other orientations

individual 3-d volumes can be combined to create the overall shape of the object

• recognition by components model
• we recognize 36 standard geons

sometimes the object is oriented in such a way that they geon becomes unrecognizable

geometric ion

different images on the two retinas

• Divided attention
• – paying attention to a number of different things at the same time – difficult
• to focus on any one thing

• Selective attention
• – focusing on specific objects of interest & ignoring others

• Eye
• movements - saccades

fixations

• (1)
• Characteristics of the scene
• – bright colors, salience, high visibility

• (2)
• Picture meaning & observer
• knowledge – scene schema (knowledge of
• what to expect in a typical scene – e.g., office scene)

• (3)
• Observer’s task
• – only fixate on areas where there is task relevant information

• Inattentional blindness
• – a stimulus that is not attended will not be perceived, even if a person is
• looking at it directly!

fill in the blanks

• No
• – if we only want to can perceive the “gist” of a scene without specific
• details

• BUT,
• Yes if we want specific details
• - only be perceived with focused attention

• When
• attention is directed to one part of an object, enhancing effect of this
• attention spreads throughout the object – “spreading
• enhancement”

• Binding
• – features such as color, form, motion & location combine to create our
• perception of the world

the binding problem

• Feature integration theory –
• at the preattentive
• stage different features of an object
• are separated – “what” stream & “where” stream

• In
• the absence of focused attention,
• features associated with one object can be incorrectly combined with another – illusory
• conjunctions

• Caused
• by damage to the parietal lobe –
• failure of attention - Balint’s
• syndrome

•  when neurons in different
• parts of the brain are firing in response to the same object their responses
• will be synchronized

• Intensity
• – brighter or dimmer

• Saturation
• – quantity of white

• Some
• wavelengths are reflected more by some objects – chromatic colors, or hues – this property –

achromatic colors

selective transmission – only some wavelengths pass through

• require at least three different
• wavelengths to create a perfect match

perceive that they have created a match with just two wavelengths

all the wavelengths stimulate cone receptors

• –each
• paint reflects only one or two colors & absorbs (subtracts) the others –
• decreases the light reaching the cone receptors

• •Monochromat – can match any wavelength in the spectrum by adjusting the intensity
• of any one other wavelength

• Generally
• hereditary, occurs in 10 out of 1 million people

• Vision
• resembles rod vision
• in dim & bright lights

• See
• everything in shades of lightness/darkness –
• white, gray, black – color blind

• Poor
• visual acuity – sensitive to bright lights & need
• to wear dark glasses

• Rod
• system is not designed to function in bright light – overloaded under strong
• illumination

need only two wavelengths to match any other wavelength

• Experience
• some color – lesser range than trichromats

• Inherited
• through the X-chromosome – sex-linked

• More
• common in males since they have only one X
• chromosome (XY)

• Females
• have two X chromosomes (XX), so even if one if dichromatic, the other normal
• chromosome compensates

• Females
• can carry the passive gene without experiencing dichromatism
• themselves

– needs three wavelengths to match any other wavelength like anynormal trichromat – BUT, will mix these wavelengths in different proportions

• •Unilateral dichromat – person with trichromatic vision in one eye & dichromatic vision
• in the other eye – extremely rare

• Protanopia
• – 1% males & .02% females – perceive
• short wavelengths (blue), as wavelength increases blue become gray
• – neutral point at around 492nm, above the neutral point they abruptly switch
• to yellow – missing long-wavelength pigment

• Deuteranopia
• – 1% males & .01% females – similar to protanopia,
• but neutral point at 498 nm – missing medium-wavelength pigment

• Tritanopia
• – very rare, .002% males & .001% females – sees blue & red, neutral
• point at 570nm – missing short-wavelength pigment

• B+Y- = increases firing to 450nm light,
• inhibits firing to 580nm light

• G+R- = increases firing to 510nm light,
• inhibits firing to 660nm light

• Y+B- and R+G- = increases firing to long wavelengths,
• inhibits firing to short wavelengths

• Color constancy
• – ability to perceive the same color under different levels of illumination –
• memory color

• Two
• areas that reflect different amounts of light look the same if the ratios of
• their intensities to the intensities of the surrounding areas remain the same

• Reflectance
• edge – the point where the reflectance of two
• edges changes – (a) vs. (b)

• Different
• cues that signal depth in a scene

• –Oculomotor cues - based on our ability to sense the
• position of our eyes & muscle tension

• –Monocular cues
• – work with one eye

• –Binocular cues
• – depend on two eyes

• –cross-eyed” pattern of eyes as they
• bring the image into focus

Deletion & Accretion

• –Deletion – farther object is covered by a
• nearer object due to the sideways movement of the observer relative to the
• object

• –Accretion – Observer moves in the other
• direction – object is uncovered

–Differences in the images on the right eye & left eye

• Corresponding retinal points – places on the retina that would
• overlap if one retina could be slid on top of the other

– imaginary circle that passesthrough the point of fixation

Impression of depth resulting from information provided by binocular disparity -

Instrument designed from this principle – camera + two lenses –

correspondence problem

–View test circles with one eye

• –View test circles through a
• peephole

• –Adding drapes to the hallway to
• eliminate reflection

our perception of an object’s size remains relatively constant even when we view an object from different distances which changes the object’s image on the retina

• – equation – as a person walksaway from you, the size of the person’s image on the retina (R) gets smaller,but
• your perception of the person’s distance (D) gets larger. These two
• changes balance each other – you perceive the person’ size(S) as remaining constant

– look constantly at a stimulus(bright light) for about a minute, blink & to focus on a blank surface –you will see an “afterimage” of the object

Farther the afterimage, larger the perceived size – Emmert’s Law

– perception that matches the actual physical world

• Misapplied size constancy scaling – cues that help us perceive 3-D
• create illusions when applied to objects on a 2-D surface

line perception depends on two cues

–Actual length of lines

–Overall length of figures

• –The line on the right appears
• longer because overall length of the figure is longer

The horizontal line on top appears longer–Depth information makes is appear farther away

Woman on the right appears much larger

• The actual structure of the room is not visible when you look through a
• peephole

• Missing depth information – we judge relative size based on how much of the room the object
• fills

• Woman on the left has a much smaller visual angle than the one on the
• right

Moon on the horizon appears much larger than when it is up in the sky

• –
• Horizon & elevated moons have same visual angle – but horizon moon appears
• to be farther away since it is on the horizon (it looks closer when it is in
• the sky directly above) – we believe the horizon moon is larger – apparent-distance theory

–

• –Moon
• appears smaller when it is surrounded by larger objects – large expanse of sky
• – angular-contrast theory