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

Comprehensive vocabulary flashcards covering color perception, depth and size perception, visual motion perception, and scene perception.

Visible light wavelength range

The spectrum of electromagnetic radiation detectable by the human visual system, spanning approximately $400\text{--}700\,\text{nm}$.

Reflection

The process by which light energy striking a surface is redirected back toward the eye or its point of origin.

Absorption

The process in which a material takes up light energy rather than transmitting or reflecting it.

Transmission

The process by which light conveys or passes through a transparent or translucent material, such as a colored filter.

Spectral reflectance function

A plot depicting the percentage of light reflected by an object across each wavelength in the visible spectrum.

Subtractive color mixing

Color mixing achieved by combining paints or pigments, where each added substance absorbs portions of the spectrum and the shared reflected wavelengths determine the resulting color.

Additive color mixing

Color mixing achieved by superimposing lights of different wavelengths, directly combining their physical light energies.

Blue paint mixed with yellow paint

An example of subtractive color mixing where both paints absorb most wavelengths except the medium wavelengths, which are reflected in common to appear green.

Blue light mixed with yellow light

An example of additive color mixing where overlapping short, medium, and long wavelengths combine to stimulate all cone types and appear white.

Hue

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

Saturation

The perceptual dimension of color representing its purity or vividness relative to neutral grayness.

Value

The perceptual dimension of color indicating its perceived lightness or darkness.

Spectral colors

Monochromatic colors that are present naturally within the rainbow or visible electromagnetic spectrum.

Nonspectral colors

Colors that do not correspond to any single wavelength of the spectrum and instead result from mixtures of different wavelengths (such as magenta or brown).

Spectral sensitivity

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

Principle of univariance

The principle stating that an infinite set of wavelength and intensity combinations can elicit the exact same response from a single photoreceptor class, preventing one receptor from uniquely determining wavelength.

Cone abundance order

The prevalence ranking of human cone photoreceptors from least to most common: S-cones (least), M-cones, and L-cones (most).

Trichromatic theory

The Young-Helmholtz theory stating that color vision is defined and encoded by the relative ratio of activation across three distinct cone classes (S, M, and L).

Metamers

Physically different wavelength mixtures that evoke the identical profile of cone responses and are therefore perceived as identical in color.

Opponent-process theory

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

Negative color afterimage

An afterimage that appears on a neutral surface following adaptation to a color stimulus, displaying the complementary opponent color (such as green after adapting to red).

Single-opponent cortical cell

A visual neuron with a receptive field organized to respond to uniform chromatic color contrast within a local region.

Double-opponent cortical cell

A visual cortical neuron that integrates spatial and chromatic opponency across its receptive field to detect colored edges and boundaries.

Cytochrome oxidase blobs

Cylindrical, color-sensitive regions located within primary visual cortex (V1) identified by high concentrations of the enzyme cytochrome oxidase.

Cerebral achromatopsia

The loss of color vision caused by cortical brain damage rather than abnormalities in the retinal photoreceptors.

Color constancy

The visual system's capacity to perceive a surface as maintaining a constant color despite substantial changes in the spectral composition of illumination.

Lightness constancy

The perception that a surface remains a stable shade of white, gray, or black under varying levels of illumination.

Problem of the illuminant

The computational ambiguity that the light reaching the retina is the product of surface reflectance multiplied by the illuminant's spectral power distribution.

Spectral power distribution

The physical light energy emitted by a light source (illuminant) measured across each wavelength.

Binocular summation

The combination of visual information from both eyes that improves performance on visual detection and discrimination tasks compared to monocular viewing.

Probability summation

The statistical increase in detection probability gained simply by having two independent detectors (eyes) rather than one.

Binocular disparity

The horizontal geometric difference between the retinal images of the same visual scene formed in the left and right eyes.

Stereopsis

The three-dimensional perception of depth produced directly by binocular disparity.

Occlusion

A monocular pictorial depth cue where a nearer object physically blocks or obstructs part of a more distant object.

Relative height

A monocular depth cue on a ground plane where objects located higher in the image plane are perceived as more distant.

Relative size

A monocular depth cue where, among objects known or assumed to be of similar size, those producing smaller retinal images appear farther away.

Familiar size

A monocular depth cue based on prior cognitive knowledge of an object's typical real-world physical dimensions to estimate viewing distance.

Linear perspective

A monocular depth cue where lines that are physically parallel in the world appear to converge toward a distant vanishing point.

Texture gradient

A monocular depth cue where repeated surface texture elements appear progressively smaller and more densely spaced as viewing distance increases.

Aerial perspective

A monocular depth cue where distant objects appear hazier, fainter, and less distinct due to atmospheric light scattering.

Motion parallax

A monocular, motion-produced depth cue where movement of the observer causes closer objects to sweep across the retina faster than distant objects.

Deletion

A dynamic occlusion depth cue where head or observer movement causes a nearer surface to progressively cover more of a farther object.

Accretion

A dynamic depth cue where head or observer movement causes a nearer surface to uncover more of a farther object.

Accommodation

The oculomotor adjustment by which the ciliary muscles alter lens curvature, causing the lens to round up (fatten) for near targets and flatten for distant targets.

Convergence

An inward rotation of both eyes required to bring the images of a nearby visual target onto the foveae of both retinas.

Corresponding retinal points

Locations on the two retinas that share identical horizontal and vertical coordinates relative to the respective foveae.

Horopter

The imaginary spatial curve containing all points in the visual field that project to corresponding retinal points at a given fixation distance, creating zero disparity.

Crossed disparity

The sign of binocular disparity produced by an object positioned closer than the fixation distance, where images displace to the right in the left eye and to the left in the right eye.

Uncrossed disparity

The sign of binocular disparity produced by an object situated farther than the fixation distance, where images displace 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 retinal disparity is small enough to yield binocular single vision rather than diplopia.

Stereoscopic correspondence problem

The computational challenge of matching corresponding visual features between the left and right retinal images to determine binocular disparity.

Disparity-selective V1 neurons

Binocular visual cortical neurons tuned to discharge maximally to specific magnitudes of crossed, uncrossed, or zero disparity.

Stereoacuity

The smallest angular difference in binocular disparity that an observer can reliably resolve to perceive depth.

Strabismus

A visual condition characterized by ocular misalignment, where one eye's line of sight deviates inward (esotropia) or outward (exotropia), disrupting binocular fusion.

Binocular rivalry

The perceptual phenomenon occurring when incompatible or non-matching images presented dichoptically to each eye alternate in conscious awareness rather than merging.

Binocular suppression

The active neural inhibition of visual input from one eye so that its conflicting image is eliminated from conscious perception.

Size constancy

The perceptual mechanism ensuring that an object's perceived size remains relatively stable despite changes in viewing distance and retinal image size.

Holway and Boring experiment

A classic experiment showing that when depth cues are progressively eliminated, perceived size judgments become dictated solely by retinal image angle rather than true physical size.

Ponzo illusion

A visual illusion in which converging linear perspective lines cause the upper of two physically identical horizontal lines to be perceived as significantly longer.

Müller-Lyer illusion

A geometric illusion in which two physically equal lines appear unequal in length due to inward- or outward-pointing arrowheads at their ends.

Ames room illusion

A distorted trapezoidal room designed to look cubical through a peephole, causing equal-sized individuals situated in different corners to appear drastically unequal in height.

Moon illusion

The perceptual illusion in which the moon appears larger near the horizon than when high at its zenith, despite casting an identical visual angle of approximately $0.5^\circ$.

Real motion

The actual physical displacement of a stimulus through space across time.

Illusory motion

The conscious perception of visual movement in a stimulus that is physically stationary.

Induced motion

An illusion where a stationary object appears to move due to the movement of nearby surrounding context (such as the moon appearing to move behind drifting clouds).

Apparent motion

The illusory perception of smooth, continuous motion produced by the rapid sequential alternation of stationary stimuli at different spatial locations.

Motion aftereffect

The visual illusion where prolonged exposure to a moving stimulus causes a subsequent stationary scene to appear to move in the opposite direction.

Interocular transfer

The transfer of an adaptation effect (such as motion aftereffect) from an adapted eye to the unadapted eye, demonstrating that the underlying processing occurs in visual cortex.

Reichardt detector

A neural motion-detecting circuit that evaluates signals from spatially separated receptors by incorporating an asymmetric delay and a multiplication cell acting as an AND gate.

Aperture problem

The ambiguity where a moving edge viewed through a narrow opening or receptive field cannot uniquely specify its true global direction of movement.

Area MT / V5

The extrastriate visual cortical area specialized for integrating local direction signals to compute global visual motion.

Saccade

A rapid, ballistic eye movement that rapidly shifts gaze from one point of visual fixation to another.

Saccadic suppression

The brief reduction in visual sensitivity surrounding saccadic eye movements that prevents the perception of visual smear.

Image displacement signal (IDS)

The sensory signal generated when an image moves across photoreceptors on the retina while the eye remains stationary.

Corollary discharge signal (CDS)

An efference copy of a motor command sent to eye muscles that is transmitted to the brain's visual comparator to predict retinal displacement.

Comparator

A neural mechanism that compares corollary discharge signals with retinal image displacement signals to distinguish observer-generated motion from world motion.

Real-motion neurons

Extrastriate cortical neurons that discharge when an object physically moves across their receptive fields, but remain inactive during eye movements across a stationary scene.

Mirror neuron

A neuron that discharges both when an individual executes a goal-directed action and when observing another individual perform the same action.

Event boundary

The perceived transition point in time that delineates where one event ends and a subsequent event begins.

Scene

A real-world visual environment containing background elements and multiple objects organized in a meaningful spatial arrangement.

Gist

The fundamental semantic character and general layout of a scene that can be apprehended during a brief glance lasting under $100\,\text{ms}$.

Selective pathway

The visual pathway through which focused spatial attention selects individual objects and binds their independent feature dimensions.

Non-selective pathway

The rapid visual pathway that simultaneously extracts scene-wide summary statistics, spatial layout properties, and overall semantic gist without focused attention.

Feature integration theory

Anne Treisman's theory proposing that elementary visual features are processed preattentively in parallel, but require focused spatial attention for correct binding into object representations.

Preattentive stage

The automatic processing stage preceding selective attention in which primitive features (color, orientation, size, depth, motion) are extracted independently.

Focused attention stage

The visual processing stage in which spatial attention binds isolated features together to form a unified, coherent object percept.

Illusory conjunction

A perceptual binding error where features belonging to different stimuli in a brief or overloaded display are incorrectly combined into an erroneous percept.

Binding problem

The computational challenge of integrating independent attributes (color, shape, motion, depth) processed in separate cortical areas into a unified perception of a single object.

Balint syndrome

A neurological condition caused by bilateral parietal lobe damage characterized by severe attentional deficits, including simultanagnosia.

Simultanagnosia

An attentional deficit in Balint syndrome where an individual can consciously perceive only one object at any given moment.

Feature search

A visual search task where the target differs from distractors by a single salient feature, yielding fast search times that do not increase with display size.

Conjunction search

A visual search task where the target is defined by a combination of two or more features, requiring focused attention and showing increased reaction times as display size grows.

Display size effect

The finding that visual search response time increases as the number of distractor items in a display increases, characteristic of conjunction searches.

Ensemble statistics

The statistical summary properties (such as average size, orientation, or color distribution) extracted from a group of items without identifying individual elements.

Scene schema

A person's knowledge and expectations concerning the types of objects typically found within a specific real-world setting.

Semantic regularities

The predictable associations, identities, and spatial placements of objects that normally occur in specific environmental contexts.

Boundary extension

The perceptual and memory phenomenon where observers remember seeing a wider, more expansive field of view around a scene than was physically present in the stimulus image.