Vision

This flashcard set contains numerous and extensive definitions, examples, and concepts of our perception of color, light, edges, etc. in the visual system. Taken from Behavioral Neuroscience (Breedlove & Watson, 2023), I made this set as a study guide for Exam 3 in Behavioral Neurobiology at BYU-I.

Wavelength

The distance between two peaks in a repeated stimulus, such as light or sound

Photons

Quanta in the range of electromagnetic energy called light (the range human visual systems can respond to)

Cornea

The transparent outer layer of the eye, whose fixed curvature bends light rays to form images on the retina

Lens

The structure in the eye that helps focus images onto the retina with the help of ciliary muscles

Refraction

The bending of light rays through density changes of a medium, like the cornea or lens of the eye

Ciliary muscles

The muscles controlling the lens shape through various contractions in a process called accommodation

Accommodation

The focusing of a sharp image on the retina by the ciliary muscles and lens of the eye

Pupil

An aperture (opening) in the iris that allows light to enter the eye

Iris

The circular structure of the eye with an opening that forms the pupil

Extraocular muscles

Three pairs of muscles attached to the eyeball that control rotational position and movement

Retina

The receptive surface inside the eye that contains photoreceptors and other neurons

Photoreceptors

The receptor cells in the retina that detect and respond to light

Rods

A class of retinal photoreceptors most active at low light levels

Cones

A class of retinal photoreceptor cells responsible for color vision and acuity

Bipolar cells

Interneurons of the retina that take information from photoreceptors to retinal ganglion cells

Retinal ganglion cells (RGCs)

Cells in the retina whose axons form the optic nerve

Optic nerve (CN II)

The collection of ganglion cell axons that extend from the retina to the optic chiasm, where they form the optic tract

Horizontal cells

Specialized retinal neurons that make contacts among receptor cells and bipolar cells

Amacrine cells

Specialized retinal neurons that connect the bipolar cells and RGCs, especially significant in inhibitory interactions of the retina

Rhodopsin

The specialized photopigment receptor molecules in the rods

Two parts of the photopigments in the eye

RETINAL (retinaldehyde) and opsins

RETINAL (retinaldehyde)

A component of photopigments that dissociates from opsin molecules in response to light, activating G protein transducin

Transducin

A G protein that activates PDE in response to light hitting the photopigment

Phosphodiesterase (PDE)

An enzyme activated by transducin that breaks apart second messenger cGMP, thereby closing ion channels

Scotopic system

A retinal system involving the rods that operates at low levels of light, with high convergence from rods to RGCs

Photopic system

A system in the retina involving the cones that operates at high levels of light and are sensitive to color, with low convergence from cones to RGCs

Visual field

The whole area you can see without movement of the eyes or head

Visual acuity

Sharpness of vision

Fovea

The central portion of the retina packed with the most photoreceptors, thereby being the center of our gaze with high visual acuity

Optic disc

Retinal region with no receptor cells because RGCs and blood vessels exit the eyeball here

Blind spot

The portion of the visual field where light falls on the receptor-less optic disc

Saccades

Quick eye movements that bring parts of the visual scene to the fovea for sharp visual acuity

Lateral inhibition

The phenomenon in which interconnected neurons inhibit neighboring neurons to enhanced contrast at edges of regions (through horizontal cells)

Scotoma

A blind region caused by damage to the brain or visual pathway

ON-center bipolar cells

Retinal bipolar cells excited by light in the receptive field’s center

OFF-center bipolar cells

Retinal bipolar cell inhibited by light at the center of its receptive field

The four dorsal (outer) layers of the LGN are called _______, while the two ventral (inner) layers are called _________.

Parvocellular (large cells), magnocellular (small cells)

Simple cortical cells (bar/edge detectors)

Cells in the visual cortex that respond best to an edge/bar with particular width, orientation, and location in the visual field

Complex cortical cells

Cells in the visual cortex that respond best to bars of particular sizes and orientations anywhere within a particular area of the visual field

Spatial-frequency filter model

Suggests Fourier analysis of visual stimuli (combining low spatial frequency from sharp details with high spatial frequency like shapes and contours)

Hue

A dimension of light perception from blue to red

Trichromatic hypothesis

A theory of color perception that suggests three different cone types excited by different regions of spectrum with separate pathways

Opponent-process hypothesis

The idea that color vision is dependent on opposite responses to light of different wavelengths - four unique hues, three opposing pairs of color (blue/green, green/red, black/white)

Spectrally opponent cells

Visual receptor cells with opposite firing responses to different regions of the spectrum

+L/-M cell

Neurons excited by L cones (sensitive to red wavelengths), inhibited by M cones (sensitive to green wavelengths)

L cones are most sensitive to the wavelength perceived as the color _______.

Red

M cones are more sensitive to wavelengths perceived as the color _______.

Green

S cones are more sensitive to wavelengths perceived as the color _______.

Blue/violet

+(L+M)/-S cells

Neurons excited by L and M cones (red/green wavelengths) and inhibited by S cells (blue/violet wavelengths)

Ventral processing stream

Visual pathway responsible for the identification of objects (“What” stream), involving the visual cortex

Dorsal processing stream

Visual pathway responsible for perceiving location of objects and guiding movement toward them (“Where” stream), involving the superior colliculi

Optic ataxia

Difficulty reaching for and grasping objects despite correct identification, caused by damage to the posterior parietal cortex

V5 function

An extrastriatal cortical region involved in the perception of continuous motion and

V1 (primary visual cortex) function

Perceiving objects and events, forming mental images

V2 function

Extrastriatal cortical region involved in the perception of illusory contours

V4 functions

Color perception, due to abundance of color-sensitive cells, and spatial domain for orientation and spatial frequency

Four dimensions of visual stimuli represented in V1

1) Location in the visual field, particularly fine mapping of central foveal vision, 2) ocular dominance, 3) orientation, 4) color

Ocular dominance columns

A cortical region where one eye provides larger degrees of synaptic input

Ocular dominance slabs

Slabs of visual cortex in which neurons of all layers respond preferentially to stimulation of one eye

Orientation column

A column of visual cortex that responds to rod-shaped stimuli of particular orientations

Mirror neurons

Neurons active when individuals make a particular movement or observe other individuals making that same movement, highly distributed in the premotor cortex

Myopia

The inability to focus retinal images of far away objects (nearsightedness), from the elongated eyeballs making the images focus in front of the retina rather than on the retina

Greater light exposure can _______ the incidence of _______ in children (visual deficiency)

Decrease, myopia

Amblyopia

Reduced visual acuity of one eye not caused by optical/retinal impairments, caused by misalignment in early development that results in suppressing inputs from one eye

Macular degeneration

The progressive loss of central vision due to death or obstruction of retinal photoreceptors

Dry macular degeneration

Visual impairment caused by atrophy of retinal pigmented epithelium, killing the overlying photoreceptors

Wet macular degeneration

Visual impairment caused by abnormal growth of retinal capillaries, resulting in detachment of the retina and/or death of photoreceptors

Visual pathway

RGCs - (optic nerve - chiasm - optic tract) - LGN of the thalamus - (optic radiations) - V1 - extrastriate cortex