brain

Visual field

The entire region of space visible to the eyes, including both binocular and monocular areas.

Binocular visual field

The portion of the visual field seen by both eyes simultaneously.

Nasal retina

The half of the retina closest to the nose; these axons cross at the optic chiasm.

Temporal retina

The half of the retina closest to the temples; these axons remain uncrossed.

Fovea dividing line

A vertical line through the fovea that separates the nasal and temporal retina.

Partial decussation

Crossing of nasal retinal axons at the optic chiasm while temporal axons stay ipsilateral.

Left visual field representation

Processed in the right cerebral hemisphere.

Right visual field representation

Processed in the left cerebral hemisphere.

Optic nerve lesion

Loss of vision in one entire eye.

Optic chiasm lesion

Bitemporal hemianopia (loss of peripheral vision in both eyes).

Optic tract lesion

Homonymous hemianopia (loss of the same visual field side in both eyes).

Primary target of optic tract

Lateral geniculate nucleus (LGN) in the thalamus (~90% of fibers).

Superior colliculus

Controls orienting movements of the eyes and head toward visual stimuli.

Pretectum

Controls the pupillary light reflex.

Hypothalamus (visual role)

Regulates circadian rhythms based on light information.

LGN location

Thalamus.

LGN layer organization

Six layers that keep inputs from the two eyes separate.

Eye segregation in LGN

Inputs from each eye project to distinct LGN layers.

Alternative names for V1

Striate cortex, Brodmann area 17.

Layer receiving most LGN input

Layer 4C of V1.

Ocular dominance columns

Striped regions in V1 where neurons prefer input from one eye over the other.

Layer 4C property

Monocular neurons (respond to only one eye).

Layers 3 and 4B

Binocular neurons that integrate input from both eyes but are still dominated by one.

Orientation of ocular dominance columns

Run perpendicularly through the cortical layers.

Binocular receptive field

Receptive field driven by inputs from both eyes.

Binocular disparity

Difference in image position between the two eyes; allows depth perception.

Orientation selectivity

Property of V1 neurons responding best to a bar of a particular angle.

Direction selectivity

Property of V1 neurons responding best to movement in a specific direction.

Dorsal stream (“where/how” pathway)

Processes motion, spatial awareness, and visually guided actions.

Ventral stream (“what” pathway)

Processes color, shape, object identity, and includes face-recognition regions.