Sensation and Perception: Color, Motion, Scene, and Depth Perception

A comprehensive vocabulary review card set spanning visual sensation and perception topics including color vision, space and depth perception, scene perception, and visual motion processing.

Visible Light Spectrum

The narrow band of electromagnetic radiation ranging from approximately $400\text{--}700\,\text{nm}$ that can be detected by the human visual nervous system.

Reflection

The process of redirecting energy (such as light) that strikes a surface back toward its point of origin.

Absorption

The process by which matter takes up light or energy instead of reflecting or transmitting it.

Transmission

The process in which light conveys through a medium, such as a transparent material or colored filter.

Refraction

The altering of the course (bending) of a wave of energy that passes from one medium into another, such as light traveling from air into water.

Spectral Reflectance Function

A plot or mathematical function indicating the percentage of light reflected by an object across each wavelength in the visible spectrum.

Subtractive Color Mixing

The mixing of pigments or paints where each added substance absorbs portions of the light spectrum, leaving only the mutually reflected wavelengths to reach the observer.

Additive Color Mixing

The creation of color perception that occurs when lights of different wavelengths are superimposed so that their energies combine.

Hue

The perceptual dimension of color corresponding to the chromatic category, such as red, green, blue, or yellow.

Saturation

The perceptual purity, richness, or vividness of a color compared to grayness.

Value

The perceptual dimension of color specifying lightness or darkness, reflecting relative luminance.

Spectral Colors

Colors evoked by a single wavelength or band of wavelengths present directly in the visible rainbow spectrum.

Nonspectral Colors

Colors that do not correspond to any single wavelength in the spectrum because they are mixtures of other wavelengths (such as magenta or brown).

Spectral Sensitivity

The relative visual sensitivity or responsiveness of a photoreceptor or visual cell to different wavelengths across the electromagnetic spectrum.

Principle of Univariance

The principle stating that an infinite set of wavelength-intensity combinations can elicit an identical response from a single photoreceptor class, meaning one photoreceptor type alone cannot make color discriminations.

Trichromatic Theory

The theory proposing that the visual system codes color through the pattern of activity across three distinct cone receptor classes: short (S), medium (M), and long (L) wavelength-sensitive cones.

Cone Abundance Order

The relative prevalence of human cone photoreceptor types ordered from least common to most common: S-cones, followed by M-cones, followed by L-cones.

Metamers

Physically different mixtures of light wavelengths that elicit identical responses from the three cone classes and therefore produce identical perceived colors.

Opponent-Process Theory

Ewald Hering's theory that color perception is governed by three antagonistic neural mechanisms: red versus green, blue versus yellow, and black versus white (light versus dark).

Negative Color Afterimage

A visual sensation seen after prolonged viewing of an adapting stimulus whose colors are complementary to the original stimulus (e.g., green after viewing red, blue after viewing yellow).

Cytochrome Oxidase Blobs

Peg-like, color-sensitive regions found in layers 2 and 3 of the primary visual cortex (V1) that stain heavily for the metabolic enzyme cytochrome oxidase.

Cerebral Achromatopsia

A neurological condition characterized by the loss of color vision caused by damage to specific cortical areas, despite normal retinal cone functioning.

Single-Opponent Cortical Cell

A cortical neuron whose receptive field responds to uniform color contrast across its center and surround, comparing chromatic inputs across local regions.

Double-Opponent Cortical Cell

A cortical cell in V1 combining spatial and chromatic opponency (e.g., center: $+L/-M$, surround: $-L/+M$), optimal for detecting colored borders and boundaries.

Color Constancy

The perceptual tendency of a surface to appear roughly the same color despite significant variations in the spectral composition of the illuminating light source.

Illuminant

The ambient light source (such as the sun, a lamp, or overcast sky) that shines upon and illuminates surfaces in an environment.

Spectral Power Distribution

A physical measurement detailing the amount of light energy present at each wavelength emitted by a specific illuminant.

Binocular Summation

The combination of visual inputs from both eyes, resulting in improved visual performance and detection sensitivity relative to viewing with one eye alone.

Probability Summation

The statistical increase in detection probability gained simply by having two independent detectors operating simultaneously rather than one.

Binocular Disparity

The slight geometric difference between the two retinal images of the same visual scene arising from the horizontal separation of the two eyes.

Stereopsis

The vivid three-dimensional visual perception of depth computed directly from binocular disparity.

Occlusion

A monocular depth cue where a nearer object physically blocks or obstructs the view of part of a farther object.

Relative Height

A monocular pictorial depth cue where objects located higher in the visual field on a ground plane appear farther away from the observer.

Relative Size

A monocular pictorial depth cue based on the fact that when two items are of similar actual size, the one subtending a smaller retinal image is perceived as farther away.

Familiar Size

A monocular depth cue where an observer relies on prior knowledge of an object's physical dimensions to judge its absolute distance based on its retinal size.

Linear Perspective

A monocular pictorial depth cue in which lines that are physically parallel in the environment appear to converge toward a vanishing point with increasing distance.

Texture Gradient

A monocular depth cue where repeated surface elements become progressively smaller, denser, and more closely packed as distance increases.

Aerial Perspective

A monocular pictorial depth cue in which distant objects appear hazier, less distinct, and bluer due to the scattering of light through atmospheric particles.

Motion Parallax

A dynamic monocular depth cue produced by observer movement, wherein closer stationary objects appear to move rapidly in the opposite direction while distant objects move slowly.

Deletion

A dynamic motion-produced depth cue in which a moving observer sees the edge of a nearer object progressively occlude (cover up) a farther object.

Accretion

A dynamic motion-produced depth cue in which a moving observer sees a farther object progressively unmasked (uncovered) from behind a nearer object.

Accommodation

The physiological oculomotor process where the ciliary muscles contract to loosen the zonules of Zinn, causing the crystalline lens to round up to focus near objects.

Convergence

An oculomotor triangulation depth cue in which both eyes rotate inward toward the nose to fixate an object that is moving closer.

Divergence

An oculomotor depth cue in which both eyes rotate outward away from each other to fixate an object that is located farther away.

Corresponding Retinal Points

Points on the two retinas that would coincide if the two retinas were superimposed point-for-point, having equal horizontal and vertical distances from their respective foveas.

Horopter

The curved surface in space (Vieth-Müller circle) defined by all points whose images fall onto corresponding retinal locations in the two eyes, yielding zero binocular disparity.

Crossed Disparity

The binocular disparity produced by an object located in front of the horopter, whose retinal image is displaced to the right in the left eye and to the left in the right eye.

Uncrossed Disparity

The binocular disparity produced by an object located behind the horopter, whose retinal image is displaced to the left in the left eye and to the right in the right eye.

Panum's Fusional Area

The narrow region of space immediately in front of and behind the horopter within which images from the two eyes can be fused into a single unified binocular percept.

Diplopia

Double vision occurring when an object falls outside Panum's fusional area, generating binocular disparity too large for the visual system to fuse.

Random Dot Stereogram (RDS)

A pair of synthetic images containing randomly placed dots that contain no monocular depth cues, demonstrating that disparity alone is sufficient to generate stereopsis.

Disparity-Selective Neuron

A binocular cortical neuron (found in V1 and MT) tuned to fire maximally when visual stimulation occurs on specific noncorresponding regions of the two retinas.

Stereoscopic Correspondence Problem

The neural computational challenge of determining which feature in the left eye's retinal image corresponds to which feature in the right eye's retinal image.

Uniqueness Constraint

A computational rule applied in solving binocular correspondence stating that a given visual feature in one eye can match at most one feature in the other eye.

Continuity Constraint

A computational rule applied in stereopsis assuming that, except at abrupt object boundaries, neighboring points in space typically lie at similar depths from the observer.

Visual Angle

The angle subtended by an object at the lens of the eye, determined jointly by the object's physical size and its viewing distance from the observer.

Size Constancy

The perceptual mechanism whereby an object is judged to remain constant in physical size despite dramatic variations in the size of its retinal projection across viewing distances.

Size-Distance Scaling

The hypothetical mechanism expressed by $S = R \times D$, where perceived size ($S$) is calculated by multiplying the retinal image size ($R$) by perceived distance ($D$).

Ames Room Illusion

A distorted room constructed with trapezoidal walls and sloping floors viewed through a monocular peephole, making two people of identical size appear radically different in stature.

Moon Illusion

The perceptual phenomenon in which the full moon appears considerably larger when viewed near the horizon than when viewed high at its zenith in the sky.

Binocular Rivalry

The dynamic perceptual competition between the two eyes that occurs when incompatible, distinct dichoptic stimuli are simultaneously presented to corresponding retinal areas.

Stereoacuity

A clinical and perceptual measure of the smallest binocular disparity threshold that can reliably generate a conscious perception of relative depth.

Strabismus

A visual condition characterized by ocular misalignment, preventing simultaneous binocular foveal fixation on a single point in space.

Esotropia

A subtype of strabismus in which one eye exhibits an abnormal inward (nasal) deviation.

Exotropia

A subtype of strabismus in which one eye exhibits an abnormal outward (temporal) deviation.

Scene

A view of a real-world environment containing background spatial layout elements and multiple objects organized in a meaningful relationship with each other.

Gist

The global semantic meaning and overarching character of a scene extracted extremely rapidly during a brief glance without requiring voluntary exploratory eye movements.

Preattentive Stage

In Feature Integration Theory, the initial automatic, pre-conscious visual processing stage where basic low-level features (color, orientation, motion) are extracted in parallel across the visual field.

Feature Integration Theory (FIT)

Anne Treisman's theoretical framework positing that primitive visual features are analyzed preattentively in parallel, but focused spatial attention is strictly necessary to bind these features to an object.

Illusory Conjunction

A psychological error in which features belonging to separate objects in a visual display are mistakenly combined during brief presentation or divided attention.

Balint Syndrome

A severe neuropsychological disorder resulting from bilateral parietal lobe damage, marked by an inability to attend to and bind features of more than one object at a time (simultanagnosia).

Binding Problem

The computational problem of correctly linking diverse feature representations (color, orientation, motion) processed in anatomically separate cortical regions into a single unified object representation.

Feature Search

A visual search task where the target differs from all distractors by a single salient visual attribute (e.g., color or orientation), producing efficient parallel 'pop-out' search unaffected by set size.

Conjunction Search

A visual search task where the target is defined by the co-occurrence of two or more distinct features, requiring serial, focused spatial attention that scales with set size.

Spatial Layout

A macroscopic description of a scene's overall geometric envelope and physical structure (such as degree of openness or ruggedness) without identifying specific isolated objects.

Ensemble Statistics

Implicit summary statistical descriptions (such as mean orientation, average size, or textural distribution) representing an ensemble of items across a spatial area without conscious identification of individuals.

Scene Schema

An internalized cognitive framework or expectation regarding what specific objects, configurations, and spatial arrangements typically belong inside a given context or setting.

Boundary Extension

A visual memory phenomenon wherein observers recall having seen a wider expanse of a scene beyond the actual boundaries of the image originally viewed.

Bayesian Approach to Perception

A statistical framework formalizing perception as the optimal combination of incoming sensory data (likelihood) with prior knowledge about the probabilities of world states ($P(A|O) \propto P(A) \times P(O|A)$).

Real Motion

The physical displacement of an object across physical space over time.

Illusory Motion

The conscious subjective perception of visual motion in the absence of actual physical movement across space.

Induced Motion

An illusion where movement of a large surrounding visual context causes a nearby stationary object to appear to move in the opposite direction.

Apparent Motion

The illusion of continuous, smooth motion produced by rapidly flashing stationary stimuli at adjacent locations in alternating temporal succession.

Motion Aftereffect

The illusory perception of movement in a stationary stimulus in the direction opposite to that of a moving stimulus to which the visual system was previously adapted.

Interocular Transfer

The transfer of a perceptual adaptation effect from one eye to the unadapted eye, demonstrating that the adaptation occurred at binocular cortical levels (V1 or higher).

Reichardt Detector

A biological neural circuit model for motion detection where inputs from two adjacent photoreceptors are multiplied after an asymmetric delay, conferring directional selectivity.

Aperture Problem

The phenomenon in which the true directional motion of a one-dimensional contour is ambiguous when observed strictly through a small local receptive-field aperture.

Middle Temporal Area (Area MT / V5)

An extrastriate visual cortical region specialized for motion processing, containing neurons that integrate local V1 motion signals into global motion perceptions.

Saccade

A rapid, ballistic eye movement made voluntarily or involuntarily to shift the high-acuity fovea from one fixation location to another.

Saccadic Suppression

The transient reduction of visual sensitivity that occurs immediately before, during, and after saccades to prevent the conscious perception of retinal motion smear.

Image Displacement Signal (IDS)

A sensory signal generated when an image physically sweeps across the photoreceptors on the retina.

Motor Signal (MS)

An active neural motor command sent from higher brain centers to the extraocular muscles to execute an eye movement.

Corollary Discharge Signal (CDS)

An efference copy of the motor signal sent simultaneously to the comparator structure in the brain rather than to the extraocular muscles.

Comparator

A theoretical central neural mechanism that compares incoming retinal motion signals (IDS) with copies of motor eye-movement commands (CDS) to distinguish self-motion from environmental motion.

Real-Motion Neuron

A neuron in extrastriate cortex that fires robustly when an external stimulus moves across its receptive field, but remains quiescent when the receptive field moves over a stationary stimulus due to eye movement.