NEUR2020 Neuroscience for Psychologists - Visual System

Flashcards for NEUR2020 Neuroscience for Psychologists, Lecture 5: Visual System, covering key vocabulary, pathways, eye anatomy, cortical processing, and associated disorders.

Retino-geniculate-striate pathway

The primary visual pathway involving the retina, lateral geniculate nucleus (LGN) of the thalamus, and the striate cortex (V1).

Superior Colliculus (SC)

A brain structure that receives about 10% of visual input and is involved in exogenous (stimulus-driven) orienting and emotion (via SC-pulvinar-amygdala pathway).

Decussation

The partial crossing of optic nerve fibers at the optic chiasm, sending visual field information from each eye to the contralateral hemisphere.

Retinotopic organisation

A mapping principle where adjacent points in the visual field map onto adjacent points on the retina, and this spatial arrangement is maintained in subsequent visual processing areas.

Cortical magnification

The phenomenon where more cortical tissue is dedicated to processing the central visual field (fovea) than the peripheral visual field.

Receptive field (RF)

The specific region on the retina (and thus the visual field) where light must fall to change the firing rate of a particular neuron.

Cornea

1. The transparent outer layer of the eye where most light bending (refraction) occurs to focus images. 2. A component of the eye responsible for initiating image formation and light bending.

Lens

A flexible structure in the eye that fine-tunes image formation through an adjustable accommodation reflex, which stiffens with age.

Iris

The contractile tissue in the eye that regulates the size of the pupil, controlling light entry and focal length.

Pupil

The opening in the iris that regulates the amount of light entering the eye and influences focal length.

Retina

The light-sensitive layer at the back of the eye containing photoreceptors for light transduction and layers of neurons for early signal processing.

Retinal Ganglion Cells (RGCs)

The final layer of neurons in the retina whose axons bundle together to form the optic nerve, transmitting visual signals to the brain.

Fovea

A small, specialized central depression in the retina responsible for high-acuity, detailed central vision due to a high concentration of cones and fewer overlying cells.

Optic disc

The point on the retina where RGC axons leave the eye to form the optic nerve, creating a 'blind spot' as it lacks photoreceptors.

Blind spot

The area on the retina corresponding to the optic disc, where there are no photoreceptors, leading to a natural gap in vision that is 'completed' by the brain.

Completion

The process by which the visual system fills in gaps in visual information, such as the blind spot or scotomas, using surrounding visual data.

Rods

Photoreceptors in the retina characterized by high sensitivity, low positional acuity (due to high convergence), and responsibility for scotopic (low light) vision; roughly 120 million per retina.

Cones

Photoreceptors in the retina characterized by lower sensitivity, high positional acuity (due to low convergence), and responsibility for color perception and photopic (well-lit) vision; there are three types (S, M, L wavelength).

Lateral inhibition

A neural process in the retina where activated photoreceptors inhibit the activity of their neighboring receptors, enhancing visual contrast and making edges appear sharper.

Mach bands

An optical illusion caused by lateral inhibition, where faint light or dark bands appear near edges in a smooth luminance gradient, exaggerating perceived contrast.

Thalamus

A major sensory relay station in the brain for all sensory input except smell, also integrating bottom-up and top-down cortical projections.

Lateral Geniculate Nucleus (LGN)

The visual relay nucleus within the thalamus, receiving axons from the optic nerve and projecting to the primary visual cortex; it has 6 layers that separate visual streams for each eye and P/M channels.

P channel (Parvocellular pathway)

A visual stream originating in the LGN, responsible for processing details, color, and fine texture.

M channel (Magnocellular pathway)

A visual stream originating in the LGN, responsible for processing motion and broad outlines.

Primary Visual Cortex (V1)

The first cortical area to receive visual information, located in the occipital lobe (also known as striate cortex); its key function is to identify object boundaries and integrate basic contrast information.

Simple cortical cells

Neurons in V1 (typically layer 3) that detect specific line segments or edges (e.g., bars of light, dark bars, single straight edges) with particular orientations and retinotopic locations; they are monocular.

Complex cortical cells

Neurons in V1 with larger receptive fields than simple cells, responding to straight-edge stimuli anywhere within their RF and firing continuously as a line or edge traverses the RF; many are binocular and involved in depth perception.

Binocular disparity

The slight difference in the position of an object's image on the retinas of the left and right eyes, which complex cells detect and use to contribute to stereoscopic depth perception.

Columnar organisation

The arrangement of functionally similar cells (e.g., sharing the same receptive field location, orientation preference, or ocular dominance) into vertical columns within the primary visual cortex (V1).

Scotoma

An area of partial or complete blindness in a part of the visual field, typically caused by damage to the primary visual cortex (V1), often without conscious awareness due to completion.

Blindsight

A condition in which individuals with damage to V1 report no conscious visual perception within a scotoma but can still respond accurately to visual stimuli (e.g., motion, location) in that area, possibly mediated by subcortical pathways.

Extrastriate cortex

Visual areas located beyond V1 in the occipital lobe, characterized by extensive interconnections and distributed processing of different visual features like color, movement, and shape.

V5 (MT)

A cortical area within the extrastriate cortex, also known as the middle temporal area, primarily responsible for motion perception; damage to this area can cause akinetopsia.

V4

A cortical area within the extrastriate cortex, primarily associated with the processing of color and form.

Dorsal stream

One of two major visual pathways, extending into the posterior parietal cortex, involved in spatial awareness, object location, direction of motion ('where' or 'how' pathway), and visually guided actions.

Ventral stream

One of two major visual pathways, extending into the inferior temporal cortex, involved in object recognition, identification, meaning, and visual memory ('what' pathway).

What vs Where theory

A theory proposing that the dorsal stream specializes in visual spatial perception ('where'), while the ventral stream specializes in visual pattern recognition ('what').

Action vs Perception theory

A theory proposing that the dorsal stream specializes in visually guided behavior ('action'), while the ventral stream specializes in conscious visual perception.

Akinetopsia (Motion Blindness)

A neurological condition resulting from damage to cortical area V5 (MT), characterized by a profound inability to perceive smooth motion, often experienced as a series of still snapshots.

Visual Agnosia

A broad term for the inability to recognize visual objects, despite intact vision, sensory input, and general cognitive function; typically classified into apperceptive and associative types.

Apperceptive Agnosia

A type of visual agnosia where the individual has a loss of visual perception, resulting in impaired drawing and an inability to identify objects.

Associative Agnosia

A type of visual agnosia where the individual has a loss of visual meaning (difficulty linking an object to its knowledge), resulting in unimpaired drawing but an inability to name objects.

Prosopagnosia (Face Blindness)

A category-specific visual agnosia characterized by a severe impairment in recognizing faces, even familiar ones or one's own, often due to damage to the right inferior temporal lobe, particularly the Fusiform Face Area (FFA).

Fusiform Face Area (FFA)

A region in the right inferior temporal lobe that is critically involved in face recognition; damage to this area can lead to prosopagnosia.