Perception: Color, Space, Scenes, and Motion

Vocabulary flashcards covering color perception, spatial depth and size, scene processing, and visual motion perspective.

Reflect

To redirect something that strikes a surface—especially light, sound, or heat—usually back toward its point of origin.

Absorb

To take up something—such as light, noise, or energy—and not transmit it at all.

Transmit

To convey something (such as light) from one place or thing to another.

Refract

To alter the course of (bend) a wave of energy that passes into something from another medium, as water does to light entering it from the air.

Reflectance curve

A plot of the percentage of light an object reflects at each visible wavelength.

Subtractive mixture

Colors made by mixing paints.

Additive mixture

Colors made by superimposing lights.

Spectral colors

Colors that appear in the visible spectrum.

Nonspectral colors

Colors, such as magenta and brown, that do not appear in the visible spectrum because they are mixtures of other colors.

Hue

The perceptual dimension representing the specific color that we perceive.

Saturation

The perceptual dimension describing how much white or light has been added into a color.

Value

The perceptual dimension referring to light versus dark; a lighter color has a higher value, whereas a darker color has a lower value.

Spectral sensitivity

The sensitivity of a cell to different wavelengths of electromagnetic radiation.

Univariance

The principle that an infinite set of wavelength-intensity combinations can produce exactly the same response from one type of photoreceptor, meaning one receptor type cannot discriminate wavelength.

Trichromacy

The theory that the color of any light is defined by the relationship among three numbers: the outputs of the S-, M-, and L-cones.

Opponent-process theory

The theory stating that three combinations of color pairs (red-green, blue-yellow, and black-white) cannot be seen simultaneously.

Metamers

Different mixtures of wavelengths that look identical because they produce the exact same three cone responses.

Negative afterimage

An afterimage whose polarity is opposite to the original stimulus, in which red produces green, yellow produces blue, and light produces dark.

Cytochrome oxidase

An enzyme present in blobs within V1 that appear to respond to color.

Cerebral achromatopsia

A loss of color vision caused by damage to the cortex.

Single-opponent cells

Cortical cells with receptive fields like retinal ganglion and LGN cells (e.g., L+ in the center and M- in the surround) that may compare local areas, responding maximally when the center stimulus matches their tuning.

Double-opponent cells

Cortical cells that resemble simple cortical cells (e.g., L+M- in the center with the opposite in the surround) that compare neighboring areas and respond best to an edge between colors.

Color constancy

The perceptual phenomenon whereby a surface appears about the same color under a wide range of illuminants.

Binocular summation

The combination of signals from both eyes that improves visual performance, including probability summation where two independent detectors lower detection miss rates.

Stereopsis

A vivid 3D depth perception produced by binocular disparity that is not available with one eye.

Occlusion

A pictorial monocular depth cue where a nearer object blocks part of a farther object, establishing depth order based on the accidental-viewpoint concept.

Relative height

A pictorial depth cue where, on the ground plane, more distant objects form retinal images that are higher and smaller.

Linear perspective

A pictorial monocular cue where parallel lines in the world appear to converge toward a vanishing point in the retinal image.

Texture gradient

A monocular cue where same-sized items produce smaller retinal images when farther away, causing a smooth size change that makes a surface look tilted in depth.

Atmospheric perspective

A monocular depth cue (also known as haze) resulting from the atmosphere scattering light, causing distant objects to look fainter and less distinct.

Motion parallax

A monocular motion cue arising from head movement where visual information gathered by one eye at two different places and times resembles information gathered by two eyes at once.

Accommodation

An oculomotor depth cue in which the lens alters its shape to focus, flattening for distant gaze (unaccommodated) and fattening for near gaze (accommodated).

Vergence

A binocular oculomotor triangulation cue involving the inward turning (convergence) or outward turning (divergence) of the eyes to place an image on corresponding retinal points.

Corresponding retinal points

Regions on the two retinas that are the exact same distance from the fovea in each eye, as well as the two foveas themselves.

Horopter

The surface of zero disparity consisting of the spatial locations of objects whose images fall on corresponding retinal points.

Absolute disparity

The visual angle measuring how far an object's image deviates from corresponding points, which is zero on the horopter and grows with distance from it.

Relative disparity

The difference between the absolute disparities of two separate objects.

Crossed disparity

The type of disparity created by objects located in front of the horopter.

Uncrossed disparity

The type of disparity created by objects located behind the horopter.

Panum’s fusional area

The region immediately in front of and behind the horopter where binocular single vision is possible; stimuli outside this area appear double.

Random dot stereograms

Stimuli containing no monocular depth cues in which stereoscopically visible figures represent cyclopean stimuli.

Correspondence problem (depth)

The challenge of determining which part of the left eye's retinal image matches which part of the right eye's retinal image.

Visual angle

The angle that an object subtends on the retina, determined jointly by the object's physical size and its distance from the observer.

Size constancy

The perceptual phenomenon in which an object's perceived size stays about the same across viewing distances even though its retinal image size changes.

Size-distance scaling

The perceptual mechanism governed by $S = R \times D$, where perceived size ($S$) depends on the product of retinal image size ($R$) and perceived distance ($D$).

Binocular rivalry

The competition between the two eyes for control of visual perception that occurs when completely different stimuli are presented to corresponding retinal points.

Suppression

The visual system's inhibition of an image presented to one eye so that it is not consciously perceived.

Strabismus

A visual condition characterized by misaligned eyes, causing an object to project onto the fovea of one eye and a nonfoveal location in the other.

Esotropia

A type of strabismus where one eye turns inward.

Exotropia

A type of strabismus where one eye turns outward.

Scene

A view of a real-world environment that contains background elements and multiple objects organized in a meaningful way relative to each other and the background.

Gist

The essential or primary character of a scene that can be gleaned in a very brief glimpse without voluntary eye movements.

Preattentive stage

The initial visual processing stage that occurs automatically, rapidly, and without conscious effort before selective attention is deployed, analyzing features independently.

Focused attention stage

The processing stage where attention is actively directed to specific objects so their individual features can be bound together into a complete perception.

Feature integration theory

A framework stating that basic visual features can be processed in parallel preattentively, but binding features correctly to objects requires attention.

Illusory conjunction

An erroneous combination of features from different objects in a visual scene, such as reporting a red K when the display contains red letters and K's but no red K.

Balint syndrome

An attentional deficit resulting from parietal lobe damage that impairs feature binding and conjunction searches while sparing feature searches.

Feature search

A visual search for a target defined by a single salient attribute, such as a distinct color or orientation.

Conjunction search

A visual search for a target defined by the simultaneous presence of two or more attributes among distractors sharing individual features.

Binding problem

The challenge of tying together separate visual attributes (such as color, form, and motion) processed by different neural circuits into a single, unified perceptual object.

Spatial layout

The global description of a scene's structure and spatial properties without reference to the identity of specific objects contained within it.

Ensemble statistics

Knowledge about the aggregate properties of a group of objects or a spatial region without knowing details about any individual item.

Scene schema

An observer's top-down knowledge and cognitive expectations regarding what objects and arrangements typically occur within a given scene.

Boundary extension

A memory and perceptual phenomenon where observers use semantic regularities to infer and mentally fill in visual content that lies beyond the physical borders of a viewed scene.

Event boundary

The point in time when one perceived environmental event ends and another begins.

Mirror neuron

A specialized neuron that responds both when an individual performs a goal-directed action and when they observe another individual performing that same action.

Induced motion

The illusory movement of a stationary object caused by the physical movement of a nearby object.

Apparent motion

The illusory impression of smooth, continuous motion resulting from the rapid alternation of objects presented in different spatial locations in rapid succession.

Middle temporal area (MT)

A higher visual cortical area containing motion-sensitive neurons tuned to specific directions and speeds, critical for motion perception.

Motion aftereffect

The illusory perception of movement in a stationary stimulus that occurs following prolonged exposure to a continuously moving stimulus.

Interocular transfer

The transfer of an adaptation effect or aftereffect from one eye to the untested eye, indicating that processing takes place in V1 or higher visual areas.

Aperture problem

The ambiguous motion percept that occurs when viewing an object through a restricted opening, where a single detector can signal a direction different from the true motion of the whole object.

Saccade

A rapid, abrupt eye movement made voluntarily or involuntarily to change visual fixation from one location or object to another.

Saccadic suppression

The temporary reduction of visual sensitivity that occurs during saccadic eye movements to eliminate the perception of retinal image smear.

Image displacement signal (IDS)

A signal generated by retinal receptors when an image shifts across the retina.

Motor signal (MS)

A command sent directly from the motor cortex to the eye muscles instructing them to move.

Corollary discharge signal (CDS)

A duplicate copy of the motor signal sent to a neural comparator rather than to the eye muscles.

Comparator

A visual system mechanism that compares incoming corollary discharge signals (CDS) and image displacement signals (IDS) to distinguish true environmental motion from self-generated eye movements.