Senses and Perception: Vision

Flashcards covering key vocabulary and concepts from the lecture on the visual system, including light and the eye, retinal processing, eye movements, receptive fields, primary visual cortex, and cortical streams.

Visible Light Spectrum

Sunlight is filtered through the atmosphere and reflected from surfaces; electromagnetic energy with wave and charged particle properties that differs in intensity and wavelength.

Visual Field

Area of space in which the eye sees its surroundings, with retinal projection being a small, inverted 2-D image distorted by the curvature of the eye, but perceived as 3-D, large, upright and stable.

Photopic Vision

Vision in bright sunlight ranging from 10 candela/m2 to 900,000,000 cd/m2.

Mesopic Vision

Vision in light levels below 10 cd/m2 to 0.0001 cd/m2, such as white paper in bright moonlight.

Scotopic Vision

Vision in very low light levels such as a moonless clear night sky.

Duplex Retina

Vertebrates have this instead of extra eyes, it contains different types of visual interneurons for switching between night and day vision.

Sensory Adaptation

When light changes, sensitivity thresholds increase or decrease over time in cones or rods, respectively, maximising contrast coding for better vision.

Cone Opsins

Differ in their wavelength-specific affinity to absorb light (S, M, and L opsins); only one opsin type is expressed per cone in the human retina.

Opsin

Light-sensitive protein (G-protein coupled receptor molecule) in the membrane of photoreceptors bound to the chromophore retinal (needed for transduction).

Rhodopsin

Opsin expressed by all rods.

Fovea

Area in the retina with the highest visual acuity; contains only cones.

Impressionism

Art movement where artists captured perceptual qualities of light, colour and atmosphere, influenced by new colour technologies and scientific discoveries about light and visual perception.

Cataract

Clouding of the lens in the eye caused mainly by aging.

Serial Connections

How the visual pathway starts in the retina: from photoreceptors to bipolar cells to ganglion cells, whose axons form the optic nerve.

Horizontal and Amacrine Cells

Cross-connections between retinal layers. Horizontal cells receive inputs from photoreceptors and project to bipolar cells. Amacrine cells receive inputs from bipolar cells and project to ganglion cells.

Geniculate-Striate Visual Pathway

Visual pathway essential for conscious vision: Retina – LGN (lateral geniculate nucleus) of the thalamus – V1 (primary visual cortex).

Extrageniculate Pathways

Visual pathway, for example: Retina – superior colliculus (SC) – pulvinar nucleus of the thalamus (pulvinar).

Saccades

Rapid eye movements or jumps to direct the fovea to collect information about the visual scene.

Fixations

Brief pauses between saccades where the eye remains relatively still to stabilize vision.

Superior Colliculus (SC)

Brain area responsible for the automatic control of eye movements.

Frontal Eye Fields (FEF)

Brain area responsible for the conscious control of eye movements.

Receptive Field

Area of the visual field where light influences a cell's activity; formed by cones converging on a bipolar cell, and bipolar cells converging on a ganglion cell.

Mach Bands

Optical illusion where stripes with low-contrast edges are perceived as having enhanced contrast at the edges.

ON-Center/OFF-Surround

A type of receptive field in bipolar and ganglion cells, where the cell is excited by light in the center and inhibited by light in the surrounding area.

OFF-Center/ON-Surround

A type of receptive field in bipolar and ganglion cells, where the cell is inhibited by light in the center and excited by light in the surrounding area.

Hypercolumn

A functional unit in the primary visual cortex (V1) composed of one left-eye and one right-eye ocular dominance column, several orientation columns, and blobs.

Orientation Columns

Columns in V1 containing simple and complex cells that respond to specific orientations of shapes.

Ocular Dominance Columns

Areas in V1 that receive input predominantly from one eye (left or right).

Simple Cortical Cells

Neurons in V1 that respond best to an edge or bar of particular width, orientation, and location in the visual field.

Complex Cortical Cells

Neurons in V1 that respond best to a bar of particular size and orientation anywhere within a particular area of the visual field.

Blindsight

Ability of cortically blind individuals (due to V1 damage) to perform visually-guided behaviors despite lacking conscious vision.

Ventral Stream

The 'what' pathway, critical for object recognition (via V4) and located in the inferior temporal cortex.

Dorsal Stream

The 'where' pathway, involved in interacting with the world (via V5/MT) and located in the parietal cortex.