Chapter 6 - The Visual System Flashcards
Sensitivity
In vision, the ability to detect the presence of dimly lit objects
Acuity
The ability to see the details of objects
Ciliary muscles
The eye muscles that control the shape of the lenses
Accommodation
The process of adjusting the configuration of the lenses to bring images into focus on the retina
Binocular disparity
The difference in the position of the same image on the two retinas
Receptors
Cells that are specialized to receive chemical, mechanical, or radiant signals from the environment; also proteins that contain binding sites for particular neurotransmitters
Horizontal cells
Retinal neurons whose specialized function is lateral communication
Bipolar cells
Bipolar neurons that form the middle layer of the retina
Amacrine cells
Retinal neurons that are specialized for lateral communication
Retinal ganglion cells
Retinal neurons whose axons leave the eyeball and form the optic nerve
Blind spot
The area on the retina where the bundle of axons from the retinal ganglion cells leave the eye as the optic nerve
Fovea
The central indentation of the retina, which is specialized for high-acuity vision
Complex cells
Neurons in the visual cortex that respond optimally to straight-edge stimuli in a certain orientation in any part of their receptive field
Binocular
Cells in the visual system that are binocular respond to stimulation of either eye
Component theory
The theory that the relative amount of activity produced in three different classes of cones by light determines its perceived color (also called trichromatic theory)
Opponent-process theory
The theory that a visual receptor or a neuron signals one color when it responds in one way (e.g., by increasing its firing rate) and signals the complementary color when it responds in the opposite way (e.g., by decreasing its firing rate)
Complementary colors
Pairs of colors that produce white or gray when combined in equal measure
Color constancy
The tendency of an object to appear the same color even when the wavelengths of light that it reflects change
Retinex theory
Land’s theory that the color of an object is determined by its reflectance, which the visual system calculates by comparing the ability of adjacent surfaces to reflect short, medium, and long wavelengths
Secondary visual cortex
Areas of cerebral cortex that receive most of their input from primary visual cortex
Completion
The visual system’s automatic use of information
obtained from receptors around the blind spot, or scotoma, to create a perception of the missing portion of the retinal image
Surface interpolation
The process by which we perceive surfaces; the visual system extracts information about edges and from it infers the appearance of large surfaces
Cones
The visual receptors in the retina that mediate high acuity color vision in good lighting
Rods
The visual receptors in the retina that mediate achromatic, low-acuity vision under dim light
Duplexity theory
The theory that cones and rods mediate photopic
and scotopic vision, respectively
Photopoic vision
Cone-mediated vision, which predominates when
lighting is good
Scotopic vision
Rod-mediated vision, which predominates in
dim light
Photopic spectral sensitivity curve
The graph of the sensitivity of cone-mediated vision to different wavelengths of light
Purkinje effect
In intense light, red and yellow wavelengths look
brighter than blue or green wavelengths of equal intensity; in dim light, blue and green wavelengths look brighter than red and yellow wavelengths of equal intensity
Fixational eye movements
Involuntary movements of the eyes (tremor, drifts, and saccades) that occur when a person tries to fix their gaze on (i.e., stare at) a point
Saccades
The rapid movements of the eyes between fixations
Transduction
The conversion of one form of energy to another
Rhodopsin
The photopigment of rods
Absorption spectrum
A graph of the ability of a substance to absorb light of different wavelengths
Visual association cortex
Areas of cerebral cortex that receive input from areas of secondary visual cortex as well as from secondary areas of other sensory systems
Prestriate cortex
The band of tissue in the occipital lobe that surrounds the primary visual cortex and contains areas of secondary visual cortex
Inferotemporal cortex
The cortex of the inferior temporal lobe, in which is located an area of secondary visual cortex
Posterior parietal cortex
The posterior area of the parietal cortex
Scotoma
An area of blindness produced by damage to, or disruption of, an area of the visual system
Perimetry test
The procedure used to map scotomas
Hemianopsic
Having a scotoma that covers half of the visual field
Conscious awareness
The awareness of one’s perceptions; typically inferred from the ability to verbally describe them
Blindsight
The ability to respond to visual stimuli in a scotoma without conscious awareness of those stimuli
Dorsal stream
The group of visual pathways that flows from the
primary visual cortex to the dorsal prestriate cortex to the posterior parietal cortex
Ventral stream
The group of visual pathways that flows from the
primary visual cortex to the ventral prestriate cortex to the inferotemporal cortex
“Where” vs. “what” theory
The theory that the dorsal stream mediates the perception of where things are and the ventral stream mediates the perception of what things are
Retina-geniculate-striate pathways
The major visual pathway from each retina to the striate cortex (primary visual cortex) via the lateral geniculate nuclei of the thalamus
Primary visual cortex
The area of the cortex that receives direct input from the lateral geniculate nuclei (also called striate cortex)
Lateral geniculate nuclei
The six-layered thalamic structures that receive input from the retinas and transmit their output to the primary visual cortex
Retinotopic
Organized, like the primary visual cortex, according to a map of the retina
Parvocellular layers
The layers of the lateral geniculate nuclei that are composed of neurons with small cell bodies; the top four layers (also called P layers)
Magnocellular layers
The layers of the lateral geniculate nuclei that are composed of neurons with large cell bodies; the bottom two layers (also called M layers)
Contrast enhancement
The intensification of the perception of edges
Receptive field
The area of the visual field within which it is possible for the appropriate stimulus to influence the firing of a visual neuron
Monocular
Involving only one eye
On-center cells
Visual neurons that respond to lights shone in the center of their receptive fields with “on” firing and to lights shone in the periphery of their receptive fields with “off” firing
Off-center cells
Visual neurons that respond to lights shone in the center of their receptive fields with “off” firing and to lights shone in the periphery of their receptive fields with “on” firing
Simple cells
Neurons in the visual cortex that respond maximally to straight-edge stimuli of a particular width and orientation
“Control of behavior” vs. “conscious perception” theory
The theory that the dorsal stream mediates behavioral interactions with objects and the ventral stream mediates conscious perception of objects
Prosopagnosia
Visual agnosia for faces
Agnosia
A failure of recognition of sensory stimuli that is not attributable to a sensory or to verbal or intellectual impairment
Visual agnosia
A failure to recognize visual stimuli that is not attributable to sensory, verbal, or intellectual impairment
Fusiform face area (FFA)
An area of human cortex, located at the boundary between the occipital and temporal lobes, that is selectively activated by human faces
Occipital face area (OFA)
An area in the occipital lobe that is implicated in the processing of faces
Akinetopsia
A deficiency in the ability to see movement progress in a smooth fashion, which often results from damage to the MT area
Area MT
An area of cortex, located near the junction of the temporal, parietal, and occipital lobes, whose function appears to be the perception of motion
