Lecture Notes on Visual Perception, Visual Search, and Perceptual Biases (Vocabulary)

Vocabulary flashcards covering key concepts from the lecture notes on cones, vision, perception, biases, and visual search.

Cone types (trichromatic vision)

Three cone types peaked around 420 nm (blue), 534 nm (green), and 564 nm (red) that support normal color vision; missing one type leads to color blindness.

Raw sensitivity function

The baseline sensitivity curve for photoreceptors, shown as a dotted line peaking near 498–490 nm, representing initial receptor responsiveness across wavelengths.

Eccentricity

Distance from the fovea in degrees of visual angle; how far from where you’re directly looking something is.

Fovea

The central retinal region with high cone density and no rods; where sharpest vision occurs.

Rod distribution

Rods are absent in the fovea and peak around 20–30 degrees from the fovea, supporting low-light vision.

Photoreceptor density function

The retinal map of photoreceptor density (cones and rods) across eccentricities; cones remain in the periphery, rods peak away from the fovea.

Visual field horizontal extent

Approximate horizontal span of about 180–190 degrees, varying with individual pupillary distance.

Pupillary distance (PD)

The distance between the eyes (roughly 52–70 mm across people) that affects horizontal field extent.

Vertical field extent

Approximate vertical span of about 130–140 degrees.

Degrees of visual angle

The unit used to express position/size on the retina; size/distance independent for cross-subject comparisons.

Photoreceptors do not vanish

Cones never drop to zero density anywhere on the retina; rods are absent in the fovea and rise with eccentricity.

Cones vs. rods in vision

Cones enable color/detail (bright light); rods enable motion/detecting in low light but do not convey color.

Optic disc (blind spot)

Where ganglion axons leave the retina; no photoreceptors there, but the brain fills in the gap.

Peripheral color vision

Color vision persists in the periphery because cones extend beyond the fovea; not limited to the center.

Template theory

A theory proposing explicit templates for every possible object; energy-inefficient and impractical for real vision.

Feature representation (early vision)

The brain encodes basic features (orientation, color, terminations) in early visual areas; objects are built later from these features.

Adaptation

Neurons fatigued by sustained stimuli reveal perceptual aftereffects indicative of neural representation changes.

Negative aftereffect

After adapting to a stimulus, perception shifts in the opposite direction to the adapting stimulus.

Feature integration theory

Theory that combines simple features into objects in higher-level processing; discussed as the building block for object perception.

Scene grammar / seed grammar

Lifelong learned expectations about where objects should appear and what environments are appropriate.

Semantic environment violation

An object is in a plausible scene but semantically inappropriate for that context (e.g., toilet paper in a dishwasher).

Syntactic/physical violation

An object appears in a physically implausible location (e.g., toilet paper floating in midair).

Gestalt grouping principles

Heuristics the brain uses to perceive groups and objects: proximity, similarity, closure, good continuation, common fate, Prägnanz.

Proximity

Elements close to each other are perceived as a single group.

Similarity

Elements with similar features (color, shape) are grouped together.

Closure

We perceive complete shapes even when contours are incomplete.

Good continuation

We perceive smooth, continuous contours, even across occlusion.

Common fate

Elements moving together are perceived as part of the same object or group.

Prägnanz (simplicity)

The tendency to interpret complex patterns in the simplest, most stable form.

Light-from-above assumption

The default assumption that light comes from above, guiding interpretation of shading.

Oblique effect

Higher sensitivity to horizontal/vertical orientations; small angle deviations are more noticeable than oblique angles.

Thatcher illusion

A face with inverted features (eyes/mouth swapped) appears grotesque when upright but less noticeable when inverted.

Upright face advantage

Faces are recognized more accurately and quickly when presented upright than inverted.

Visual search

Task of locating a target among distractors; used to study attention and feature vs. conjunction processing.

Pop-out search (feature search)

Target differs by a single diagnostic feature (e.g., color); reaction time is independent of set size.

Set size

Number of distractor items in a search array; used to measure how search difficulty scales.

Conjunction search

Target defined by a combination of features; reaction time increases with set size due to serial search.

Minimum information principle (satisficing)

The brain represents just enough information to perform a task cheaply and quickly.

Agnosia

Impairment in recognizing objects or categories (e.g., prosopagnosia for faces); can be genetic or brain injury–related.

Object reconstruction

The process of turning early-feature representations into coherent object representations in higher-level cortex.

Other-race effect

People tend to recognize faces of their own race more accurately due to training/data exposure; similarly biases in computer vision.

Bias in computer vision

Algorithms reflect training data biases; performance can be worse for underrepresented groups.