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29 Cards in this Set

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  • Back
through what steps mught our eyes have evolved from
photoreceptors--> concentrate in groups to detect light, an eye spot---> grooves to shield glare, better see predetors---> cornea to cover eyes---> lens to magnify and project images---> shadows, contrast, shapes
how do cornea, iris and lens help form images
iris dosen't do anything, it is obague, makes light go through pupil
the cornea, transparent, light passes through it, helps focus light due to its curvature.
lens--- adds to focus of cornea, it can flatten for seeing farther object, become spehrical for close ups. Forms image on retina
how are cones and rods distributed, how do they respond to light
cones--- for seeing colour and under brigh light. most located in fovea. In bright light, allow for high acutity.
Cones, for sensitivity, in dim light. located everywhere except fovea. best looking at object 20 degrees away from direct lline of sight
has photochemical rhodopsin. When hit by light, chemical reaction in rods membrane, causes electrical charge, transduction, and AP occurs. In cones, also use this, but 3 diff. photoreceptors.
how do cone and rods differ
cones--- acutity and colour
- photochemical rhodopsin
- rohopsin degenrate faster
rods--- sensitivity, good for dim light
what is the chemical basis for light and dark adaptation, why do we see mostly in cones in bright light and rods in dim
in dim light. first 7 min, we see with cones b/c rods have not regenerated. after that rods are used increasing eyesite sensitivity until max out. Slow rod regeneration due to evolution of gradual darkness, not artificial light.
neural connections of retina
there are bipolar cells and ganglion cells that nead to optic nerve. in cones, concentrated in fovea, ganglion cell has smaller receptive field, more acute b/c one cone to one ganglion cell. in rods, large area with rods, many rods to one ganglion cell so larger perceptive field, but less acutity since so many rods to one cell, but also higher sensitivity b/c more rods , more electrical activity received by cell. funelling of activity from menay receptors to fewer receptor ceels= neural convergence
a spectrum of colours make light white. visible light, very small wavelength, ibjects have colour b/c they abosorb and relflect off colour. surface that reflects all light = white. absorbs all = black
short wavelenth= blue
long wavelength= red
if absorb short wavelenght, appear blue/ violet
subtractive color mizing
mixing of pigments.
additive mixing colour ---> colored lights rather than pigments mized. when all colours together, appear white.
three primary law- 3 differenct wavelengths of light can be used to make any colour
law of complementary--- pairs of wavelengths ---> colours make white
trichromatic theory
color vision is mediated by 3 types of receptors: blue, red and green.
together, you can see all colours.each receptor sensitive to different wavelengths/
colour blind ppl are dichromates. only see two wavelenths
opponent process theory
when 2 diffent colours of opposite wavelengths mix ( complementary colours ), become white
- colour mediated by cells excited or inhibited, depending on wavelength of light.
i.e. to see blue. blue cell receptor exited while its complementary, yellow, inhibited. blue, yellow opponent cells
-to distinguish dim light, have brightness detector, excited by lights of all wavelength, so even if colours cancel each other, act to concert tand excite brightness detectors
complementary afterimages
the green flag. after staring at it, the green receptors become fatigues, so when shift eyes to white, the green receptors don't respond as strongly, its complemntary colour, red shines , dosen't get cancelled out
what is the value of cisual system ability to exaggerate contrast
good contrast, see things clearer. grey tv screen producing black images.
" on/ off " receptive field
ganglion cells have an "on" "off" portion. " on" arranged in circular , and "off" is in a concentric circle around it. this arrangement causes the ganglion cell to be more sensitve to areas of contrast thanuniformaty. ganglion cells in contrast shades respond strongly. tell contrast if more of an object hits the "off" region, then less action potential then when an object hits "on" while in places of uniformity, no strong or weak AP b.c they tend to cancel each other out
how do unique receptive field in neuron in primary visual cortex provide orientation of edges
the visual neurons , " on" " off" fields are more oval. and they are arranged in many different orientations. the object being viewed matches to a particular neuron orientation, we view it. for some cells, one side is " on" the other is "off" these cells respond best when edge b/n dark and light aligned precisely along " on/ off" neurons in primary visual cortex senstive to orientation of edges or bar that stimulate them. respond max. when edge of light slanted in same orientation as long axis of oblong visual field.
spatial fequency coding
- no. of repetitions of a pattern per unit square
-width of " on" "off" receptive field distinguishing one spatial fequency from another
- sensitivity to regular patterns of change in intensity of light contribute to distinguishing one object from another
how does conetxt affect top down process of object recognition
recognizing objects also depends not only on stimuli from object but also on other stumli that might lead us to recognize object. so if we see prof in mall, not recognize him b/c don't imagine him outside of univeristy. expectationsbased on context provide part of top down contribution to object identification
pattern of movemnet provide a basis for object recognition
when attach lights to joints of humaan, by the dots moving, know if it is human, sex, large, small
Helmholtz perception as a problem solving
visual perception not passive response of visual system to the light entering eyes, but active mental process. light focused onto retinas not the scene we see but just as cues for thescene. mechanism in brain identify critical cues, construct mental representaion of world. unconcious inference to refer to active processes that underlie perception.
binocular cues for depth
eye convergence---> inward turning of eye when you look at object closer to you. Poor distance cue
binocular disparity---> slight differnt view each eye gets on object
binocular disparity
b/c each eye distance apart from each other, differnt angle. degree of disparity between the two eyes is a judge of depth. the farther object is, the less the disparity.
how to stereoscopes and autostereograms provide illusion of depth
two photographs shot at different angles
motion parallax as cue for depth
important to view depth with only one eye. change view one has as a scene or object when on's head move sideways to view object. degree of change in either eyes view at one moment compared with the next serve as cue for distance.
pictoral cues for depth
1) occlusion---> if personpartially occlues( cut off) image of tree, means man in frount of tree
2) relative image size for familiar objects---> of tree smaller than man, tree is in the background b/c we know man is smaller than tree
3_ linear perspective---> train tracks converging in distance= far off
4) texture gradient---> pebbels far off are smaller and closer together, also appear more
5) positon relative to horizon. object near horizon farther away then object farther away from horizon
6) differenctial lighting of surfact---> amount of light reflected from diff surfaces varies as orientation. if light on top, seems like object pop out. if light at bottom, object goes in.
why does size perception depend of distance perception
if object moved twice as far away, we don't see image twice as small. even though retina image is twice as small. we only see it as farther away. ability to see object in ubchanged size, despote it is farther= size constancy.
how might unconscious assesment of depth provide basis for muller- lyer, ponzo and moon illusion
one object in each illustration appear larger than other b/c of distance cues that lead it to be judged as farther away. if one is to be judged farther away, byt two produce same image on retina, then object judged farther away will be larger.
1) unconscious process judge one image to be farther than other
2) unconscious process judge object i.e. moon to be larger than usual
3) thus enter conscious, we think it is larger therefore closer b/c we know it didn't change in size
how can constancies and lightness be explained by the unconscious inference theroy
1) size constancy--- object appears to remain same size even though retinal image say it is not
2) shape constancy--> object appears to maintain same shape even htough retinal image changes shape when it is rotated in space
3) lightness constancy---> a white, gray, blk, object appears constant in degree to which it looks ligh/ dark even though amt light refelected changes when amt of light shining changes
helmholtz unconcious inference perspective
perceptioninvolves problem solving unconciously. sensory input provides cues that brain uses to figure out distance, size , movemnet
Gibson direct perception
use of info about relationship, assume relationship exist directly with sensory stimuli. higher order stimuli, perceptual system ecolved to repond to sensory stimuli directly.
how can direct perception and unconcious inference be understood as complemnts
brain extracts relavent rellationship from stimulus info.