Chapter6 Flashcards
Sensitivity
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 lens.
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.
Light
Waves of electromagnetic energy between 380-760 nanometers.
Receptors
Cells that are specialized to receive chemical, mechanical, or radiant signals demo the environment.
Horizontal cells
Type of retinal neurons whose specialized function is lateral communication.
Bipolar cells
Bipolar neurons that form the middle layer of the retina.
Amacrine cells
A type of retinal neuron whose specialized function is lateral communication.
Retinal ganglion cells
Retinal neurons whose axons leave the eyeball and form the optic nerve.
Blind spot
A gap in the receptor layer due to the optic nerve leaving the eyeball.
Fovea
An indentation at the center of the retina that is specialized for high-acuity vision. The thinning of the retinal ganglion layer reduces distortion of incoming light.
Completion
Filling in the blind spot with information provided by the receptors around the blind spot.
Surface interpolation
The process by which the visual system perceives large surfaces, by extracting information about edges and from it, inferring the appearance of adjacent surfaces.
Cones
The visual receptors of the retina that mediate high acuity color vision in good lighting.
Rods
The visual receptors of the retina that mediate achromatic, low acuity vision under dim light.
Duplexity theory
The theory that cones and rods mediate different kinds of vision.
Photopic vision
Cone-mediated vision. Predominates in good lighting and provides high-acuity color perceptions of the world.
Scotopic vision
Rod-mediated vision. Predominates in dim illumination, there is not enough light to reliably excite cones.
Nasal hemiretina
The half of each retina next to the nose.
Temporal hemiretina
The half of each retina next to the temples.
Photopic spectral sensitivity curve
The graph of sensitivity of cone-mediated vision to different wavelengths of light.
Scotopic spectral sensitivity curve
The graph of sensitivity of rod-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.
Fixation eye movements
Involuntary movements of the eyes that occur when a person tries to fix their gaze on a point (tremor, drifts, saccades)
Saccades
Small jerky movements or flicks.
Transduction
The conversion of one form of energy to another
Rhodopsin
The photopigment of rods. When exposed to intense light, it is bleached and looses its ability to absorb light. When returned to the dark, it regained its redness and ability to absorb light.
Absorption spectrum
A graph of the ability of a substance to absorb light of different wavelengths.
Visual field
The entire area that you can see as a particular movement.
Visual transduction
Conversion of light to neural signals by the visual receptors.
Pigment
A substance that absorbs light.
Retina-geniculate striate pathways
Conducts signals from each retina to the primary visual cortex/striate cortex via the lateral geniculate nuclei.
Primary visual cortex/ striate cortex
The area of the cortex that receives direct input from the lateral geniculate nuclei.
Lateral geniculate nuclei
The six-layered thalamic structures that receive input from the retinas and transmit their output to the primary visual cortex/ striate cortex.
Retinotopic
Organized, like the primary visual cortex, according to a map of the retina. There is a disproportionate representation of the fovea.
Parvocellular layers (P layer)
Particularly responsive to color, fine pattern details, and stationary or slow moving objects. Cones provide most of the input. Top four layers.
Magnocellular layers (M layer)
Particularly responsive to movement. Rods provide most of the input. Bottom two layers.
contrast enhacement
intensification of the perception of edges
ommatidia
very large receptors interconnected by a lateral neural network
lateral inhibition
receptors fires, it inhibits its neighbors via the lateral neural network
receptive field
the area of the visual field within which it is possible for a visual stimulus to influence the firing of that neuron
achromatic
uncolored light shone on the retina
monocular
each neuron had a receptive field in one eye but not the other
On-center cells
respond to lights shone in the central region of their receptive fields “on” firing and to lights shone in the periphery of their receptive fields with inhibition, followed by “off” firing when the light is turned off
Off-center cells
respond with inhibition and “off” firing in response to lights in the center of their receptive fields and with”on” firing to lights in the periphery of their receptive fields
simple cells
Neurons in the visual cortex that respond maximally to straight-edge stimuli in a certain position and orientation
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
respond to stimulation of either eye
Component theory (trichromatic theory)
theory that the relative amount of activity produced in three different classes of cones by light determines its perceived color
opponent process theory
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 (decreasing firing rate)
chromats
vision photopigments
color constancy
refers to the fact that the perceived color of an object is not a simple function of the wavelengths reflected by it
retinex theory
the color of an object is determined by its reflectance- proportions of light of different wavelengths that a surface reflects
Dual-opponent color cells
Neurons that respond to the differences in the wavelengths of light stimulating adjacent areas of their receptive field
cytochrome oxidase
an enzyme present in particularly high concentrations in the mitochondria of dual-opponent color cells of the visual cortex
blobs
peglike, cytochrome oxidase-rich, dual-opponent color columns
secondary visual cortex
those that receive most of their input from the primary visual cortex
visual association cortex
areas that receive input from areas of secondary visual cortex as well as from the secondary areas of other sensory systems
prestriate cortex
band of tissue in the occipital lobe that surrounds the primary visual cortex
infrerotemporal cortex
cortex of the inferior temporal lobes
posterior parietal cortex
areas of association cortex that receive visual input are located in several parts in several parts of the cerebral cortex–largest one
scotoma
area of blindness in the the corresponding area of the contralateral visual field of both eyes
perimetry test
The procedure used to map scotomas
hemianopsic
have a scotoma covering half of their visual field
conscious awareness
person sees something, he or she will be consciously aware of seeing it
Blindsight
the ability of such patients to respond to visual stimuli in their scotomas even though they have no conscious awareness of the stimuli
dorsal stream
flows from the primary visual cortex to the dorsal prestriate cortex to the posterior parietal cortex
ventral stream
flows from the primary visual cortex to the ventral prestriate cortex to the inferotemporal cortex
“where” versus “what” theory
vision is that damage to some areas of cortex may abolish certain aspects of vision while leaving others unaffected
“control of behavior” versus “conscious perception” theory
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
failure of recognition
Fusiform face area
an area of human cortex, located at the boundary between the occipital and temporal lobes, that is selectively activated by human faces
Akinetopsia
deficiency in the ability to see movement progress in a normal smooth fashion
MT area
middle temporal area of the cortex
