Receptive Fields: Video Notes (PSYC2007 Week 4c)

Vocabulary flashcards covering key receptive-field concepts and visual processing terms from the lecture notes.

Receptive field (RF)

The region of space where stimulation changes a cell's firing rate; the stimulus must be of the type the cell is tuned to.

Retinal ganglion cell (RGC)

Retina neuron with center–surround receptive fields; sends visual information to the LGN via the optic nerve.

Lateral geniculate nucleus (LGN)

Thalamic relay for visual information from RGCs to V1; contains centre–surround RFs.

Primary visual cortex (V1)

Cortical area where simple cells first show orientation selectivity and feed into complex and other cells.

On-centre cell

A cell that increases firing when light hits the centre of its RF; weaker or minimal response to uniform light.

Off-centre cell

A cell that increases firing when a dark spot hits the centre of its RF; little response to uniform light.

Centre-surround cell

RF with excitatory centre and inhibitory surround (or vice versa), creating spatial opponency.

Spatial opponency

Centre and surround regions provide opposing responses, enabling contrast/edge detection.

Convergence

Many photoreceptors feed into a single RG/LGN cell, enlarging receptive fields with eccentricity.

Fovea

Central retina area with high cone density and high acuity; near 1:1 cone-to-RG cell input.

Eccentricity

Angle from the line of sight; increasing eccentricity moves objects toward peripheral vision.

Spatial acuity

Resolution of vision; decreases with eccentricity due to fewer cones and more neural convergence.

Cone density

Density of cone photoreceptors; decreases with eccentricity, contributing to lower acuity away from the fovea.

Retinotopy

Topographic mapping from retina to cortex, so neighboring points in the retina map to neighboring cortical sites.

On-centre cell vs Off-centre cell

Two classes of centre–surround cells: On-centre increase with center light; Off-centre increase with center darkness.

Simple cells

V1 neurons that are orientation- and width-selective with a linear receptive field.

Complex cells

V1 neurons that are orientation-selective but have non-linear receptive fields and often respond to motion.

Hypercomplex (end-stopped) cells

V1 cells that are length/ends selective (end-stopped) and may be color-selective.

Concentric cells

RFs with circular symmetry; less orientation-specific, often color-sensitive.

Tuning curve

Plot of a neuron’s response as a function of a stimulus feature (e.g., orientation).

Tuning bandwidth

Width of the tuning curve at half-maximum; indicates how broadly a neuron is tuned.

Orientation selectivity

Preference of a neuron (often in V1) for a specific stimulus orientation.

Direction selectivity

Preference of some neurons for motion in a particular direction.

Binocular input

Some neurons receive input from both eyes, especially in V1.

Monocular receptive fields (RFs)

RFs that respond to input from only one eye.

Pooling

Combining inputs from multiple cells (e.g., LGN inputs to simple cells, then to complex cells) to form higher-order responses.

Troxler fading

Percept fades for stationary images as adaptation reduces responses when image is not moving.

Hermann grid illusion

Illusion where gray spots appear at intersections due to center–surround processing in retinal circuitry.

Brightness perception

Perceived brightness depends on On-centre cell firing; grey perceived when center response is reduced relative to surrounding.

Maintained-discharge level

Baseline firing rate a neuron maintains; a high level (around 50% of max) would be needed for single On system to encode increments/decrements.

Metabolic cost

Energy required to keep many neurons firing at baseline; high maintained activity increases energy use.

Signal-to-noise level (SNL)

Ability to detect a signal amid neural noise; higher noise lowers detectability.

Dynamic range

Range of firing rates a cell can exhibit; higher maintained levels reduce dynamic range.

Luminance level

Brightness value of a region; used to define luminance contrasts.

Luminance contrast

Difference in luminance between regions; drives edge detection and perception of brightness.

Edge detection

Extraction of boundaries in an image, often via center–surround RFs that respond to changes in luminance.

Optic chiasm

Point where nasal retinal fibers cross to the opposite hemisphere, enabling contralateral processing.

Corpus callosum

Major bridge between hemispheres; transfers visual information across the two sides of the brain.

Contralateral processing

Visual field information from one side is processed in the opposite hemisphere (e.g., left field to right hemisphere).

Hubel & Wiesel

Pioneering researchers who mapped RFs in V1 and described simple, complex, and hypercomplex cells.