Color Vision and Depth Perception Theories

problem of univariance

A single photoreceptor's response can't distinguish between a change in wavelength or intensity—why multiple cone types are necessary for color vision.

three types of cones and their peak sensitivities

S-cones (440 nm), M-cones (535 nm), L-cones (565 nm)

trichromatic theory of color vision

Color perception is based on the relative firing rates of three types of cones.

metameric matches

Different combinations of wavelengths that produce identical color perception.

opponent-process theory

Negative afterimages and the fact that red-green and blue-yellow don't blend.

opponent color pairs

Red-Green, Blue-Yellow

opponent-process theory explanation

Opponent neurons are excited by one wavelength and inhibited by its pair.

dichromacy

A form of color deficiency where one cone type is missing.

size-distance ambiguity

The same retinal image size can come from a small close object or a large distant object.

Helmholtz equation for size perception

S = R × D (Size = Retinal Image × Distance)

oculomotor cues for depth

Accommodation and convergence

monocular depth cues

Interposition, relative size, relative height, linear perspective, shadows, atmospheric perspective, texture gradient

ground cues

Linear perspective & texture gradient; provide stable depth reference

motion parallax

Closer objects move faster across the retina than distant ones when we move.

occlusion-from-motion

Objects that become covered or uncovered by others as we move.

Ponzo illusion

Identical lines appear different lengths due to linear perspective implying different distances.

Ames room illusion

Room shape tricks perception—people appear dramatically different in size.

binocular disparity

The difference in images between the two eyes; a depth cue

horopter

The set of points where images fall on corresponding points on both retinas

crossed vs. uncrossed disparity

Crossed: object is closer than the horopter. Uncrossed: object is farther.

stereopsis

Depth perception based on binocular disparity (e.g., in stereoscopes)

importance of motion in perception

It resolves size-distance ambiguity and improves object recognition.

point-light displays

Studying perception of biological motion

corollary discharge theory

How we distinguish between motion of objects vs. motion of our eyes

three signals in corollary discharge theory

Motor signal (MS), Corollary discharge signal (CDS), Image movement signal (IMS)

CDS or IMS reaching the comparator

Movement is perceived

Gibson's ecological theory

Perception is shaped by the environment and guides action; includes the concept of affordances.

optic flow

The pattern of motion in the visual field as we move through an environment.

affordances

Possibilities for action provided by the environment (e.g., a chair affords sitting).

action goals influence perception

Perception of distance can change based on physical effort or social support (Proffitt's studies).

Motor Signal (MS)

eye movement

CDS corollary discharge signal

sent to the “comparator”

IMS image movement signal

object moves position on retina gets sent to comparator to help determine if my body or the object is moving