Sensation 4

Figure–Ground Segregation

The process of distinguishing an object (figure) from its background (ground).

Illusory Contours

Edges perceived where no physical change in luminance exists, as in the Kanizsa triangle; supported by V2 neuron activity.

Inverse Projection Problem

The same retinal image can result from multiple real-world sources; the brain must infer the most likely object.

Viewpoint Invariance

The ability to recognize an object regardless of angle, position, or lighting.

Recognition-by-Components (RBC) Theory

Biederman’s theory that objects are recognized by combinations of basic 3D forms called geons.

Number of Geons in RBC Theory

Approximately 36 geons can combine to represent most objects.

Viewpoint-Dependent Theory

Tarr and Bülthoff’s theory: object recognition depends on stored 2D snapshots of familiar views.

Marr’s Computational Theory

Proposes sequential stages of object recognition: raw image → primal sketch → 2.5D sketch → 3D model representation.

Segmentation

Dividing the visual field into separate regions corresponding to objects and background.

Grouping

Combining elements into meaningful wholes using Gestalt principles.

Visual Agnosia

Inability to recognize objects despite intact vision; often caused by temporal lobe or ventral stream damage.

Apperceptive Agnosia

Failure to integrate visual features into a unified percept.

Associative Agnosia

Ability to perceive form but failure to recognize or assign meaning to it.

Prosopagnosia

Face blindness due to Fusiform Face Area (FFA) damage.

Global Precedence Effect

Tendency to process overall structure before local details (e.g., seeing the big letter in a Navon display before smaller ones).

Lateral Occipital Complex (LOC)

Brain area specialized for recognizing object shapes and forms.

Fusiform Face Area (FFA)

Brain region specialized for face perception; damaged in prosopagnosia.

Parahippocampal Place Area (PPA)

Processes spatial layout and environmental scenes (places, houses, rooms).

Extrastriate Body Area (EBA)

Processes static and moving images of human bodies and body parts.

Primary Visual Cortex (V1)

Detects edges, orientation, and basic contrast features.

Area V2

Integrates contours, boundaries, and mid-level visual information.

Area V3

Processes dynamic form and global motion information.

Area V4

Processes color and curved shape features; contributes to object recognition.

Area V5 (MT)

Specialized for motion processing and direction selectivity.

Binocular Rivalry

Phenomenon in which each eye sees a different image, and perception alternates between them.

Tong et al. (1998) Study

Used binocular rivalry; found FFA active when faces were perceived, and PPA active when houses were perceived.

Expertise Effect

The FFA can activate for non-face objects of high expertise (e.g., bird or car experts).

Gestalt Law of Prägnanz

The brain tends to perceive the simplest, most stable, and coherent form possible.

Gestalt Law of Common Fate

Elements moving in the same direction are grouped together.

Gestalt Law of Similarity

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

Gestalt Law of Proximity

Objects close to one another are perceived as belonging to a group.

Gestalt Law of Closure

The mind fills in missing edges or gaps to perceive complete forms.

Gestalt Law of Good Continuation

Lines and contours are perceived as continuous rather than disjointed.

Gestalt Law of Common Region

Elements within the same bounded area are perceived as grouped together.

Gestalt Law of Connectedness

Physically connected elements are seen as a single unit.

Gestalt Law of Symmetry

Symmetrical elements are perceived as part of the same object.