functions of color vision
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Terms in this set (40)
Adjust the mixed dosage of 3 different colors (comparison field) to match a test color (test field)
- findings:
--- Possible to match any test color by correctly adjusting the proportion of 3 wavelengths
--- Persons with normal vision always use 3 wavelengths to match any colors
--- Color deficient people can match certain colors using only two wavelengths
opponent process theory of color vision- ewald hering - 3 mechanisms matching 3 pairings of color - Opponent neurons provide an excitatory response at one end of the light spectrum, and an inhibitory response at the other endcolor deficiency- john dalton - 3 types of daltonism: --- Monochromat: use 1 wavelength to match all other ones --- Dichromat: use 2 wavelengths to match other wavelengths --- Anomalous trichromat- use three wavelengths, but to a different ratio than normal trichromatishihara platescolor deficient people see other numbers or no number at allmonochromatism- extremely rare - hereditary - only rod vision - poor visual acuitydichromatismcolors experienced to a lesser rangehow is color represented in the cortex- distributed process - Neurons responding to different colors have been found in areas V1, V2, but mostly in V4 - fMRI confirmed that color perception is involving all 3 V areas- cortical color blindess- Cerebral achromatopsia: loss of color perception following stroke or brain injury (mostly to area V4) - Cone pigments are intact but brain areas processing color are damagedcolor constancy- Color remains relatively constant under various contexts of illumination --- Indoor natural daylight --- Outdoor sunlight --- Artificial lightchromatic adaptationexposure to blue light → saturate short wavelengths and blue light experienced less intenselysurrounding effectscolors remain more or less constant when surrounded by other colorsmemory of colorknowing that trees are green, or roses are red makes us experience those colors more vividlylightness constancyRegardless of illumination conditions black always reflects 5% of light, gray reflects between 10 and 70% of light, and white reflects 80-90% of lightratio principle- Reflectance is always the same rotation of whatever ambient light is presentReflectance and Illumination edges- Reflectance edges are sharp - Illumination edges are fuzzy (shadows)lightness perception is determined by- Absolute amount of light distributed on the retina - Information about the 3D configuration of objects - Assumptions (experience related) of how illumination should be reflected - Neighboring colors/grays can also alter lightness constancycue approach to depth perception- Correlate retinal image with depths - Connections between cues and depth are learned through experience and interactions with the environment. With time these associations become automatic and we experience the world in 3D.monocular cues- cues that can be detected with one eye - pictorial cues --- occlusion: relative not absolute distance --- cast shadows: ambiguity about relative position of objects removed when shadow is added --- familiar size: knowing the actual size of objects can influence depth perception --- atmospheric perspective: distant objects are less sharp than closer objects - depth information depiction in 2D --- linear persepctives --- Albert's window allows to recreate 3D perspective pictures using a transparent grid over a scene --- Depth cue from convergence of lines to a focus point --- changes in texture gradient (density is greater far away) - movement produced cues --- motion parallax: far objects move slowly, near objects move rapidlyoculomotor cues- ability to sense position of eyes and tension in eye muscles - created by convergence (inward movement of eyes) and accommodation (change of lens shape when we focus on something)binocular cues- cues that depend on two eyes to be detected - In adults, eyes are approx. 6 cm from each other, thus world viewed from two slightly different eye positions - stereopsis: both retina have a corresponding point where they connect in the visual cortex --- forms an imaginary circle called the horopter (where foveal fixations occur)crossed and uncrossed disparity- crossed: in front of horopter (disparity moves outward) - uncrossed: beyond the horopter (disparity moves inward)Holway and Boring Experiment- participants tasked with adjusting the diameter of the comparison circle to match that of the test circle - eliminating depth cues made it more difficult to judge size accurately and participants relied more on visual anglesize constancyPerception of object's size remains relatively constant, even so object viewed from different distancesrelative sizewe can adjust size by comparing it to other objects in the environmentveridical perception- perception that matches actual physical situations - can break down visual illusionsrichard gregory- misapplied size constancy scaling - size relies on depth cues - challenges to gregory: no perspective or depth cues in "dumbbell" version and the illusion still occursday's explanationperception of length of lines depends on 2 cues for length (1) actual length of vertical lines (2) overall length of figurethe ponzo illusionaccording to gregory's misapplied scalinf explanation, top lines appear longer because of depth information making them appear farther away - corridor illusion creates an illusion similar to ponzo's because of the line perspectives in 2DAmes RoomTrapezoidal room; creates an optical illusion with one large and one small person - looks normal when viewed through the peephole due to depth cues and perspective - Both persons appear to be at the same distance, same relative base - But in reality, small person is much farther away →corresponds to a smaller visual angle than the person on the right - Same distance x smaller retinal image = smaller in size (size-distance scaling)antigravity illusion- person stands perpendicular to level ground - appears to stand at odd angle - earth's gravity hold's chair against wall - chair appears to cling without fallingmoon illusion- moon and sun appear larger on the horizon even though they're always the same distance away - Explanation: the apparent-distance theory A: filled space (terrain) →provides depth information B: empty space →no depth information - moon appears smaller on picture because camera lenses are not subject to size-distance scaling mechanism