Visual Processing

Photoreceptors

Specialized cells in the retina (rods and cones) that convert light into neural signals.

Rods

Photoreceptors that are highly sensitive to low light, do not mediate color, and have low spatial acuity.

Cones

Photoreceptors that require high light levels, mediate color vision, and provide high spatial acuity.

Fovea

The central part of the retina with the highest concentration of cones; responsible for sharp central vision.

Geniculostriate Pathway

The primary visual route for conscious perception: Retina to LGN to Primary Visual Cortex (V1).

Lateral Geniculate Nucleus (LGN)

A structure in the thalamus that receives visual input from the retina and relays it to the primary visual cortex.

Tectopulvinar Pathway

A secondary visual pathway from the retina to the superior colliculus and pulvinar; involved in orienting and fast responses.

Receptive Field (RF)

The specific region in the visual field to which a individual neuron responds.

V1 (Primary Visual Cortex)

The first cortical area to receive visual input; neurons here are tuned to simple features like line orientation.

Ventral Stream

The "What" pathway; travels from V1 to the temporal lobe; responsible for object recognition and identification.

Dorsal Stream

The "Where" or "How" pathway; travels from V1 to the parietal lobe; responsible for spatial cognition and vision-for-action.

V4

An area in the ventral stream specialized for color processing.

Achromatopsia

Color blindness caused by brain damage (specifically to area V4) rather than the eyes.

V5 (MT)

An area in the dorsal stream specialized for motion perception.

Akinetopsia

Motion blindness; a condition where motion is perceived as a series of still images rather than fluid movement.

Visual Agnosia

The inability to recognize or identify objects despite having intact basic visual sensations.

Optic Ataxia

A deficit in visually guided reaching and pointing caused by damage to the dorsal stream.

LIP (Lateral Intraparietal Area)

A region in the parietal lobe containing neurons tuned to the direction of intended movements (like saccades).

Eye-centered Frame

A coordinate system where the location of an object is represented relative to the direction of the eyes.

Head-centered Frame

A coordinate system where the location of an object is represented relative to the orientation of the head.

Double Dissociation

Research evidence where two related mental processes are shown to function independently (e.g., recognizing objects vs. reaching for them).

Allocentric Representation

Spatial coding of an object's location relative to other objects in the environment.

Egocentric Representation

Spatial coding of an object's location relative to the observer's own body.