PSY1005 Lecture 4: Receptive Fields and the Visual System

Vocabulary practice flashcards covering receptive fields, retinal ganglion cell properties, visual pathways (LGN, V1, extrastriate areas), feature detectors, binocular disparity, and the dorsal and ventral visual streams from PSY1005 Lecture 4.

Receptive Field

The specific area on a receptor surface (such as the retina for vision or the skin for touch) that, when stimulated, affects the firing rate of a neuron.

Visual Receptive Field

The area of the retina that must receive illumination or stimulation in order to generate a neural response in a given neuron.

Neural Convergence (Visual System)

A wiring arrangement in which signals from multiple photoreceptors feed into a single downstream neuron (such as a retinal ganglion cell), which increases light sensitivity at the expense of spatial acuity.

On-Centre Cell

A cell featuring a concentric centre-surround receptive field that is excited ($+$) by light falling in its centre and inhibited ($-$) by light falling in its surround.

Off-Centre Cell

A cell featuring a concentric centre-surround receptive field that is inhibited ($-$) by light falling in its centre and excited ($+$) by light falling in its surround.

Centre-Surround Antagonism

The antagonistic interaction between the centre and surround regions of a receptive field, such that stimulating the surround opposes the response elicited by stimulating the centre, resulting in maximal firing when the centre is stimulated alone and weak firing when the entire receptive field is illuminated.

Lateral Inhibition

An inhibitory neural interaction where stimulation of one receptor region dampens the activity of neighboring neurons via horizontal or interneuron connections, mediating edge detection and phenomena like the Hermann grid illusion.

Retinal Ganglion Cells (RGCs)

Sensory output neurons of the retina characterized by centre-surround receptive fields, whose axons bundle together to form the optic nerve and encode all visual information sent to the brain.

Colour Opponency (Ganglion Cells)

A receptive field organization in retinal ganglion cells that processes chromatic signals antagonistically by contrasting signals from different cone types, creating red-green ($\text{R}+\text{G}-$ / $\text{G}+\text{R}-$) and blue-yellow ($\text{B}+\text{Y}-$ / $\text{Y}+\text{B}-$) opponent channels.

Optic Chiasm

The anatomical junction where nerve fibers originating from the nasal hemiretinas decussate to the contralateral hemisphere, while fibers from the temporal hemiretinas remain uncrossed.

Lateral Geniculate Nucleus (LGN)

A visual relay nucleus in the thalamus that receives input from retinal ganglion cells representing the contralateral visual field and projects to the primary visual cortex; its cells maintain centre-surround receptive fields and retinotopic mapping.

Retinotopic Mapping

An orderly spatial arrangement in visual structures, such as the LGN and primary visual cortex, where adjacent neurons receive input from adjacent areas of the retina, preserving the spatial layout of visual space.

Primary Visual Cortex (V1 / Striate Cortex)

The first cortical area in the occipital lobe that processes visual information relayed from the LGN, containing neurons organized to detect low-level features such as orientation, line width, and binocular disparity.

Simple Cortical Cell

A neuron in the primary visual cortex ($\text{V1}$) with side-by-side excitatory and inhibitory receptive field zones, responding maximally to stationary bars or edges of light of a particular orientation.

Orientation Tuning Curve

A graphical representation showing the relationship between the angular orientation of a line or bar stimulus and the resulting impulse firing rate of a cortical visual cell.

Complex Cortical Cell

A visual cortical neuron that responds best to bars of light of a specific orientation moving across its receptive field, often with selectivity for a specific direction of movement.

End-Stopped Cortical Cell

A visual cortical neuron (formerly known as a hypercomplex cell) that responds maximally to moving corners, angles, or bars of a specific length in a specific direction, but is inhibited when the stimulus extends beyond its receptive field.

Visual Association Cortex (Extrastriate Cortex)

Cortical visual areas beyond $\text{V1}$ (including $\text{V2}$, $\text{V3}$, $\text{V4}$, and $\text{V5}/\text{MT}$) that display increasing receptive field sizes and specialize in progressively complex visual processing such as colour, motion direction, form, and disparity.

Binocular Disparity

The horizontal positional difference between the images formed on the retinas of the left and right eyes, where larger differences correspond to greater differences in physical depth.

Horopter

An imaginary curved surface in space containing all points that stimulate geometrically corresponding locations on the two retinas, defined as possessing zero binocular disparity.

Disparity-Selective Cell

A binocular neuron located in visual cortical areas that compares inputs from both eyes and fires preferentially to a specific degree and direction of binocular disparity according to its disparity tuning curve.

Ventral Stream

The visual processing pathway projecting from $\text{V1}$ to the inferotemporal ($\text{IT}$) cortex, termed the 'what' pathway or 'vision for perception', which specializes in identifying objects, shapes, textures, colours, and faces.

Dorsal Stream

The visual processing pathway projecting from $\text{V1}$ to the posterior parietal cortex, termed the 'where' pathway or 'vision for action', which specializes in determining object location, detecting motion, and guiding motor actions like reaching.

Accommodation

The physiological process by which the ciliary muscles alter the shape of the crystalline lens (responsible for $20\%$ of the eye's focusing power) to adjust focus for objects at varying distances.

Phototransduction

The biochemical process occurring in photoreceptor outer segment disk membranes where absorbed light causes a retinal molecule to change shape, triggering a molecular cascade that hyperpolarizes the photoreceptor into an electrical signal.

Dark Adaptation

The increase in visual sensitivity over time ($30\,\text{mins+}$) in the dark, characterized by a transition from cone-dominated to rod-dominated vision.

Fovea

The central retinal area possessing the highest density of cone photoreceptors and no rods, conferring the greatest spatial visual acuity.