Bio chapter 10 studyguide

visual field

The entire scene that your visual system encompasses when you fixate on one visual location

visual acuity

Sharpness of vision

macular degeneration

Degenerative disorder of the receptors at the center of the retina, leaving only peripheral vision

blind spot

Point in the visual field of each eye within which visual stimuli cannot be perceived

optic disk

Location on the retina where optic nerve fibers exit the eyeball, causing a blind spot.

nasal hemiretina (half-retina)

Medial half of the retina

temporal hemiretina

Lateral half of the retina

photoreceptors

Collective name for the retinal cells that detect and transduce light stimuli

Wavelength

The distance between two peaks of vibratory energy; in the case of light, also corresponds to hue.

brightness

One of the three dimensions of the color solid, varying from light to dark

hue

One of the three dimensions of the color solid; gives rise to what we call the “color” of a stimulus.

saturation

One of the three dimensions of the color solid; gives the intensity of a color from pale (e.g., pink) to intense (e.g., crimson).

lateral inhibition

Neural process that uses horizontal interconnections between receptors to enhance boundaries

apparent motion

The impression that a series of still pictures is in smooth motion, when the pictures are presented successively at the proper rate

refraction

Bending of light rays by an optical device

cornea

Front optical element of the eye, with fixed curvature, that performs the initial refraction of incoming light

lens

Secondary optical element of the eye, with variable curvature, that finetunes refraction to focus images on the retina

ciliary muscles

Muscles that alter the shape of the lens

accommodation

The process of altering the shape of the lens in order to focus images on the retina

pupil

Aperture in the front of the eye that controls the amount of light entering the eye

iris

Colored part of the eye that dilates and contracts to change pupillary size

Extraocular muscles

Muscles that control the movement of the eye in its socket (orbit)

retina

Lining of the back of the eye that contains the photoreceptors and other cells, and on which the incoming visual image is focused

rods and cones

The two principal types of photoreceptors

bipolar cells

Cells that interconnect the photoreceptors with the ganglion cells

ganglion cells

Cells of the retina that receive stimulation from the photoreceptors via the bipolar cells and transmit it to the brain in the form of action potentials

optic nerve

Fiber projection from the retina to the brain, consisting of the axons of ganglion cells

horizontal and amacrine cells

Retinal cells that connect across patches of receptors and ganglion cells, thereby performing local processing

scotopic system

Rod-based visual system that is especially effective in low light

photopic system

Cone-based visual system that provides color information and greater acuity

rhodopsin

Rod photopigment

opsin and retinal

The two parts of rhodopsin, liberated when rhodopsin is struck by photons

transducin and phosphodiesterase

Major players in the process by which activated opsin deactivates the cGMP cascade, resulting in receptor hyperpolarization

midget bipolars

Bipolar cells that each connect to one photoreceptor only

diffuse bipolars

Bipolar cells that each connect to a number of photoreceptors

range fractionation

System whereby sites of receptors, some with low thresholds, some with high thresholds, handle different intensities of light

fovea

Central region of the retina containing the highest density of receptors, and therefore having the greatest acuity

primary visual cortex

The part of the occipital lobe that receives the main visual projection from the LGN, centered around the calcarine sulcus; also known as V1

scotoma

Perceptual gap or “black spot” in the visual field as a result of disease or injury

blindsight

Residual capacity for non-consciously discriminating visual stimuli within a scotoma

hemineglect

Syndrome in which the half of visual space opposite a brain region is disregarded (despite preserved visual capacity)

optic chiasm

Location at which the fibers from the nasal halves of the retina cross over to the opposite hemisphere of the brain

optic tract

Name for the visual fiber pathway after it has passed the optic chiasm

striate cortex

Another name for primary visual cortex, based on its prominent stripe (corresponding to the visual inputs of layer 4)

extrastriate cortex

Collective name for visual cortical areas other than V1

retinotopic organization

Preservation of Orderly arrangement of visual pathway that corresponds to the layout of receptors on the retina

lateral geniculate nucleus

The principal thalamic nucleus concerned with vision

optic radiations

Name for the visual projection fibers from the LGN to the cortex

parvocellular and magnocellular

The two major divisions of the LGN, corresponding to the layers containing small neurons and those containing large neurons, respectively

simple cortical cells

Cortical visual neurons whose receptive fields show the best response to edges or bars of particular width, orientation, and location in the visual field

complex cortical cells

Cortical visual neurons that respond best to edges or bars of particular width and orientation located anywhere in the visual field

hypercomplex cortical cells

Cortical visual neurons that respond best to edges or bars of particular length (although other types of visual neurons also possess this property to some extent)

spatial frequency filter model

Model of visual processing that proposes that cortical neurons are actually sensitive to the spatial frequency of stimuli rather than edges, bars, and angles

Fourier analysis

Mathematical process by which, in the case of vision, a visual scene may be broken down into its component spatial frequencies and harmonics

V2

Visual cortical area, immediately adjacent to V1, that processes complex relations among parts of the visual scene, and that is sensitive to illusory contours

ocular dominance columns

Alternating bands of cortical neurons that represent each of the two eyes separately

orientation columns

Columns found within ODCs, within which all of the neurons respond to visual stimuli with the same orientation

blobs

Clusters of cells within ODCs that extend through all layers except layer 4; once thought to be especially important in color vision

cytochrome oxidase

Enzyme that is found particularly within “blobs”

trichromatic theory

Prediction that color vision would be found to be based on the presence of blue-, green-, and red-sensitive cones on the retina

opponent-process theory

Prediction that color perception would be found to arise from physiological processing giving rise to positive and negative values for the three opponent pairs: yellow and blue, green and red, and black and white

M, L, and S receptors

Cones that respond to medium-, long-, and short-wavelength light, respectively

spectrally opponent cell

Cell in which two regions of the spectrum have opposite effects on the rate of firing

V4

Region of extrastriate visual cortex that is especially concerned with the perception of color

V5

Region of extrastriate cortex that is especially concerned with the perception of motion

achromatopsia

Syndrome in which color vision is completely lost as a result of brain lesions

trichromatic

Type of vision based on three types of cones (with three different cone pigments)

dichromatic

Type of vision based on two types of cones (with two different cone pigments)

dorsal stream

System for visual processing that is especially concerned with spatial location, or “where”

ventral stream

System for visual processing that is especially concerned with recognition, or “what”

myopia

Nearsightedness

amblyopia

Deviated eye, which can lead to poor vision in that eye