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40 Cards in this Set
- Front
- Back
Law of Specific Nerve Energies
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Mueller held that whatever excited a particular nerve establishes a special kind of energy unique to that nerve. Sooo, any activity by a particular nerve always conveys the same kind of info (brain sees activity from optic nerve and hears activity from auditory nerve)
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If the optic nerve is directed into what is ordinarily the auditory portion of the brain, very early in development, what happens?
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What would have been auditory thalamus and cortex reorganized to become visual coretex, developing some (but not all) of the characteristic appearance of a visual cortex. Stimulation there produces visual experience. (Ferret study!)
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pupil
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light enters the eye through an opening in the center of the iris called the pupil
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lens
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focuses light; adjustable
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cornea
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focuses light; not adjustable
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retina
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rear surface of the eye lined with visual receptors; light from left visual field strikes right side of retina and vice versa;image on retina is reversed
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bipolar cells
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located in retina; receptors on back of the eye send messages toward biopolar cells whcih are neurons located closer to the center of the eye
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amacrine cells
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get info from biopolar cells and send to other biopolars, other amacrine cells or ganglion cells. located in retina closer to center than recepors, bipolar and ganglion
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ganglion cells
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get info from bipolar cells, located in retina but closer to the center of the eye than receptors and bipolar cells; axons join one another to loop around and travel back to the brain, forming the optic nerve
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blind spot
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point at which optic nerve exits the eye and therefore contains no receptors at this point
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fovea
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central portion of the macula; "pit"; specialized for acute detailed vision-the most precise visionl blood vessels and ganglion cell axons are absent here and receptors packed tightly leads to least impeded vision and therefore great pereception of detail; all cones
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macula
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greatest ability to resolve detail; center of retina
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ciliary muslces
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controls the lens;
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rods
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one type of receptor in the retina; most abundant in the periphery of the human retina, respond to faint light but are bleached by bright light and thus not very useful in bright daylight; more rods than cones; periphery vision is mostly rods and each receptor shares a line with tens or hundres of others
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cones
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one type of receptor in retina; most abundant in and around the fovea, are less active in dim light, more useful in bright light and essential for color vision; more direct route to brain than rods; each has own line to the brain
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Why can you see a faint star in your periphery better than when looking directly at it
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the light falls on the part of the retina with more rods which are more sensitive to faint light-more convergence of input, magnifying sensitivity to faint light
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trichromoatic theory of color vision
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aka Young-Helmholtz theory; we perceive color through the relative rates of response by three kinds of cones, each kind maximally sensitive to diff set of wavelengths; long wavelenth cones, short wavelenth and medium wavelength cones distributed randomly within the retina
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Opponent-process theory
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trichromatic theory doesn't account for all color vision like negative color afterimage; we perceieve color in terms of paired opposites:red vs green, yellow vs.blue and white vs black...no such thing as reddish-green, etc;
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Retinex Theory
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the two other theories don't explain color and brightness constancy; the cortex compares info from various parts of teh retina to determine the brightness and coor perception of each area (ex: if cortex notes a certain amount of green throughout a scene, it subtracts some green from each object to determine true color
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Color constancy
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ability to recognize the color of an object despite changed in lighting
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Long wavelength cones
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responds well to red or yellow
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medium wavelength cones
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responds best to green, less to yellow
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short wavelength cones
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responds best to blue
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horizontal cells
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rods and cones make synaptic contact with horizontal cells and bipolar cells; horizontal make inhibitory contact wit bipolar
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optic chiasm
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the optic nerve from left eye and from right eye meet at the optic chiasm; half the axons from each eye cross to the opposite die of the brain
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lateral geniculate nucleus
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axons from ganglion cells go here; it's a nucleus of the thalamus specialized for visual perception
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optic nerve
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starts at the ganglion cell axons and can lead to the lateral geniculate nucleus of the thalamus (most do) or the superior colliculous or hypotahlamus or elsewhere
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receptive field
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part of the visual field to which any one neuron responds is that neuron's receptive field; receptive field for ganglion cellwould be the combined receptive fields of all the receptors that are connected to it
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lateral inhibition
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reduction of activity in one neuron by activity in neighboring neuron
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parvocellular neurons
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type of ganglion cell; smaller cell bodies and small receptive fields, mostly in or near fovea; highly sensitive to detail because small receptive field; highly sensitive to color (excited by some and inhibited by others); connect only to LGN of thalamus
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magnocellular neurons
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ganglion cell; larger cell bodies and receptive fields, distributed fairly evenly thoughout retina; not color sensitive, respond strongly to moving stimuli and overall patterns but not details; throughout retina, including periphery; most connect to LGN but a few connect to other visual areas of thalamus
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koniocellular neurons
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ganglion cell; small cell bodies, similar to parvo but they occur throughout retina instead of clustered near fovea; connect to LGN, other parts of thalamus, and superior colliculus
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visual pathway
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photoreceptors to LGN to primary visual cortex(aka V1 or striate cortex) then goes to secondary visual cortex (V2; but V1 and V2 are reciprocal)
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primary visual cortex
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V1; responds to any kind of visual stimulus and is active even when we close our eyes and imagine visual stimuli
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secondary visual cortex
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V2; process info further and transmits to additional areas
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ventral stream
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visual paths in the temporal cortex, aka "what" pathway bc it is specialized for identifying and recognizing objects
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dorsal stream
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visual path in the parietal cortex, aka "where" or "how" pathway bc it helps motor system find objects and how to move toward them, grasp them and so forth
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simple cells
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only found in primary visual cortex; receptive field of a simple cell has fixed excitatory and inhibitory zones
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complex cells
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located in either V1 or V2 have receptive fields that cannot be mapped into fixed exciatory or inhibitory zones; it responds to a pattern of light in a particular orientations anywhere within its large receptive field, regardless of the exact location of the stimulus
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end-stopped or hypercomplex cells
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resemble complex cells but it has a strong inhibitory area at one end of its bar shaped receptive field
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