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Flashcards in Chapter6 Deck (77):
1

Sensitivity

The ability to detect the presence of dimly lit objects.

2

Acuity

The ability to see the details of objects.

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Ciliary muscles

The eye muscles that control the shape of the lens.

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Accommodation

The process of adjusting the configuration of the lenses to bring images into focus on the retina.

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Binocular disparity

The difference in the position of the same image on the two retinas.

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Light

Waves of electromagnetic energy between 380-760 nanometers.

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Receptors

Cells that are specialized to receive chemical, mechanical, or radiant signals demo the environment.

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Horizontal cells

Type of retinal neurons whose specialized function is lateral communication.

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Bipolar cells

Bipolar neurons that form the middle layer of the retina.

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Amacrine cells

A type of retinal neuron whose specialized function is lateral communication.

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Retinal ganglion cells

Retinal neurons whose axons leave the eyeball and form the optic nerve.

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Blind spot

A gap in the receptor layer due to the optic nerve leaving the eyeball.

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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.

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Completion

Filling in the blind spot with information provided by the receptors around the blind spot.

15

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.

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Cones

The visual receptors of the retina that mediate high acuity color vision in good lighting.

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Rods

The visual receptors of the retina that mediate achromatic, low acuity vision under dim light.

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Duplexity theory

The theory that cones and rods mediate different kinds of vision.

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Photopic vision

Cone-mediated vision. Predominates in good lighting and provides high-acuity color perceptions of the world.

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Scotopic vision

Rod-mediated vision. Predominates in dim illumination, there is not enough light to reliably excite cones.

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Nasal hemiretina

The half of each retina next to the nose.

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Temporal hemiretina

The half of each retina next to the temples.

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Photopic spectral sensitivity curve

The graph of sensitivity of cone-mediated vision to different wavelengths of light.

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Scotopic spectral sensitivity curve

The graph of sensitivity of rod-mediated vision to different wavelengths of light.

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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.

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Fixation eye movements

Involuntary movements of the eyes that occur when a person tries to fix their gaze on a point (tremor, drifts, saccades)

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Saccades

Small jerky movements or flicks.

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Transduction

The conversion of one form of energy to another

29

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.

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Absorption spectrum

A graph of the ability of a substance to absorb light of different wavelengths.

31

Visual field

The entire area that you can see as a particular movement.

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Visual transduction

Conversion of light to neural signals by the visual receptors.

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Pigment

A substance that absorbs light.

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Retina-geniculate striate pathways

Conducts signals from each retina to the primary visual cortex/striate cortex via the lateral geniculate nuclei.

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Primary visual cortex/ striate cortex

The area of the cortex that receives direct input from the lateral geniculate nuclei.

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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.

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Retinotopic

Organized, like the primary visual cortex, according to a map of the retina. There is a disproportionate representation of the fovea.

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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.

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Magnocellular layers (M layer)

Particularly responsive to movement. Rods provide most of the input. Bottom two layers.

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contrast enhacement

intensification of the perception of edges

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ommatidia

very large receptors interconnected by a lateral neural network

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lateral inhibition

receptors fires, it inhibits its neighbors via the lateral neural network

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receptive field

the area of the visual field within which it is possible for a visual stimulus to influence the firing of that neuron

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achromatic

uncolored light shone on the retina

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monocular

each neuron had a receptive field in one eye but not the other

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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

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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

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simple cells

Neurons in the visual cortex that respond maximally to straight-edge stimuli in a certain position and orientation

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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

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binocular

respond to stimulation of either eye

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Component theory (trichromatic theory)

theory that the relative amount of activity produced in three different classes of cones by light determines its perceived color

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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)

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chromats

vision photopigments

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color constancy

refers to the fact that the perceived color of an object is not a simple function of the wavelengths reflected by it

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retinex theory

the color of an object is determined by its reflectance- proportions of light of different wavelengths that a surface reflects

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Dual-opponent color cells

Neurons that respond to the differences in the wavelengths of light stimulating adjacent areas of their receptive field

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cytochrome oxidase

an enzyme present in particularly high concentrations in the mitochondria of dual-opponent color cells of the visual cortex

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blobs

peglike, cytochrome oxidase-rich, dual-opponent color columns

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secondary visual cortex

those that receive most of their input from the primary visual cortex

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visual association cortex

areas that receive input from areas of secondary visual cortex as well as from the secondary areas of other sensory systems

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prestriate cortex

band of tissue in the occipital lobe that surrounds the primary visual cortex

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infrerotemporal cortex

cortex of the inferior temporal lobes

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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

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scotoma

area of blindness in the the corresponding area of the contralateral visual field of both eyes

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perimetry test

The procedure used to map scotomas

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hemianopsic

have a scotoma covering half of their visual field

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conscious awareness

person sees something, he or she will be consciously aware of seeing it

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Blindsight

the ability of such patients to respond to visual stimuli in their scotomas even though they have no conscious awareness of the stimuli

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dorsal stream

flows from the primary visual cortex to the dorsal prestriate cortex to the posterior parietal cortex

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ventral stream

flows from the primary visual cortex to the ventral prestriate cortex to the inferotemporal cortex

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"where" versus "what" theory

vision is that damage to some areas of cortex may abolish certain aspects of vision while leaving others unaffected

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"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

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Prosopagnosia

visual agnosia for faces

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agnosia

failure of recognition

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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

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Akinetopsia

deficiency in the ability to see movement progress in a normal smooth fashion

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MT area

middle temporal area of the cortex