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62 Cards in this Set
- Front
- Back
Vision |
the visual system transduces electromagnetic stimuli(light) into an electrical signal(nerve impulse) |
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For vision, we need |
-stimulus -receptor to detect stimulus -a transducer to turn detection into graded electrical signals -a processor that makes sense of the electrical signal |
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Sensory Transduction |
process by which sensory stimuli are transduced into electrical potentials |
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Light |
-eyes detect presence of light -electromagnetic energy -the photon is the basic unit of light |
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More light |
-the color of an object is a result of the wavelength of light it reflects -wavelengths of between 380 and 760 nm is visible to us |
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Visual spectrum |
is not a property of the light, but a property of the reception |
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Stimulus |
perceived color of light is determined by 3 dimensions: hue, brightness, saturation |
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Hue |
the dominant wavelength |
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Brightness |
-intensity -is influenced by the amplitude of the signal |
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Saturation |
-purity -influenced by quality or purity of signal |
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Orbits |
bony front of skull in which eyes are suspended |
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Sclera |
-white outer coat of eye -holds eye in place |
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Cornea |
outer layer of the front of the eye |
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Pupil |
regulates the amount of light that enters the eye |
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Iris |
pigmented ring of muscles situated behind the cornea |
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Lens |
-altered by contraction of ciliary muscles -changes shape and permits eye to focus on images of near or distant objects |
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Vitreous humor |
-fills main part of eye -jelly, gelatinous fluid |
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Retina |
-contains photoreceptors |
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Fovea |
-central point of the retina -responsible for most acute vision -contains only cones |
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Optic disk |
-exit point from the retina -axons of the ganglion cells that form the optic nerve -responsible for the blind spot |
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Anatomy of the Visual System |
-image must be focused on retina -sensory receptors(photo receptors) located in retina -retina is actually part of the brain -retina and optic nerve are in the CNS |
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Photoreceptors |
-receptors facing backwards(away from front of eye) -light must pass through nervous tissue before activation photoreceptors |
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More photoreceptors |
-specialized type of neuron found in the retina that is capable of phototransduction -convert light into neural signals -photoreceptor proteins in the cell that absorb photons triggering a change in the cell's membrane potential |
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Rods |
-photoreceptors -very sensitive -easily bleached -concentrated in the periphery -poor acuity -useful in the dark |
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Cones |
-photoreceptor -not very active in dim light -essential for color vision -daytime vision -small features of the environment -highest acuity/sharpness -located in fovea |
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3 types of cones that differ in the wavelength they absord |
-long=red -medium=green -short=blue |
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Color blindness |
-inability to see color under normal lighting -lack of cones that perceive color |
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Red-green color blindness |
-protanopia -dueteranopia -protanomaly |
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Blue-yellow color blindness |
-tritanopia -tritanomaly |
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Phototransduction |
-molecule changes when light strikes it -changes shape -causes chain reaction that ultimately affects action potentials |
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Photopigments |
-phototransduction -light causes bleaching of the photopigment contained in the photoreceptor -photopigments are unstable chemicals that are sensitive to different wavelengths of light -rhodopsin & iodopsin |
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Rhodopsin |
-naturally pinkish and bleaches to a pale yellow when it is exposed to light it breaks into retinal and opsin -splitting of the photopigment produces the receptor potential |
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Dark adaptation |
-rhodopsin bleaches in response to light -rods are sensitive to light and take longer to fully adapt to changes in light -cones take about 10 minutes to adapt to the dark |
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Negative afterimage |
-image continues to appear in one's vision after the exposure to the original image has ceased -caused when eye's photoreceptors adapt to overstimulation and lose sensitivity -photoreceptors that are constantly exposed to the same stimulus will eventually exhaust their supply of photopigment resulting in a decrease in signal to the brain |
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Bipolar cell |
-receive info from the photoreceptors -sends info to the ganglion cells -synapse with rods or cones(or horizontal cells) -unlike most neurons biopolar cells communicate via graded potentials rather than action potentials -receptive fields are made up of photoreceptor cells |
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Ganglion cell |
-receives info from bipolar cells -axons give rise to the optic nerve |
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Horizontal cell |
interconnects adjacent photoreceptors and the outer processes of the bipolar cells |
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Amacrine cell |
interconnects adjacent ganglion cells and the inner processes of the bipolar cells |
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Visual phototransduction |
-photoreceptors are tonically active(depolarized) -when light hits them, they hyperpolarize causing a decrease in the amount of glutamate released -their synapse onto the biopolar cell in inhibitory |
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Receptive field |
-point in the visual field that an individual neuron responds to -location of the receptive field depends on the location of the photoreceptors that provide it with visual info -receptor to axon ratio |
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Periphery of retina |
-many receptors coverage to single ganglion cell -large area of visual field |
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Fovea |
-similar number of ganglion cells and cones |
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Center-surround receptive fields |
-off & on -circular field -on-center- responds most when light strikes center -off center- responds most when light strikes out portion of receptive field -Hubel & Weisel |
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2 types of bipolar cells |
-on -off |
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Receptive fields of bipolar cells |
-2 parts= center and surround(they are both mutually antagonistic) -The surround with respond in opposite direction from the center -the center is more sensitive but the surround is larger |
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ON-CENTER |
+= excitation to inhibition to dark |
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OFF-CENTER |
-= excitation to dark inhibition to bright |
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Retinal ganglion cells |
-different populations of ganglion cells that send visual info to the brain -3 types -90% of axons in the optic nerve go to the lateral geniculate nucleus -parallel processing form M,P, K ganglion cells in the retina for visual construction and perception |
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Receptive field of a ganglion cell |
-center & surround -response are not graded, but are true action potentials -strong stimulus will lead to higher frequency of action potentials |
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Optic chiasm |
-optic nerve from both eyes meet and cross at the optic chiasm -at this point, the info coming from both eyes is combined and then splits according to the visual field -corresponding halves of the visual field are sent to left and right halves of the brain for processing -right side of primary visual cortex deals with left half of the visual field from both eyes |
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Primary visual pathway |
-axons from ganglion cells serve nasal halves of retina cross to the other side of the brain -each hemisphere receives info from contralateral half of visual scene |
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Light hits retina |
-image is inverted from cortex lens onto the retina -all images processed by opposite side of eye than you think-convex lens -nasal and temporal fibers -nasal fibers cross -temporal fibers do not |
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Lateral geniculate nucleus |
-thalamus -6 layers -1,4,6 correspond to info from contralateral fibers of the nasal retina -2,3,5 correspond to ipsilateral fibers to temporal retina |
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More, lateral geniculate nucleus |
-layers also respond to magnocellular, parvocellula, koniocellular cells differently. |
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Primary visual cortex |
-largest system of human brain -visual processing -areas V1-V5 -flow of info through hierarchy |
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Visual association ares |
-as info passes through visual hierarchy, complexity of neural representation increases -neural representation may come at a level of specialization into 2 distinct pathways |
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Dorsal stream |
-where/how -spatial attention |
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Ventral stream |
-what -recognition, identification, categorization |
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Color vision |
-different mechanisms at different levels of the system |
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Trichromatic theory |
-condition of processing 3 independent channels for conveying color info -derived from 3 cone types |
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Opponent process color theory |
-human visual system interprets info about color by processing signals from cones and rods in an antagonistic manner -3 types of comes have some overlap in wavelengths of light |
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Opponent-process coding |
-neurons respond specifically to pairs of primary colors, red opposing green and blue opposing yellowish -retina contains 2 kinds of color sensitive ganglion cells: red-green, yellow-blue |