BioPsych Chp 6-10
Terms
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- Law of Specific Nerve Energies
- 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)
- If the optic nerve is directed into what is ordinarily the auditory portion of the brain, very early in development, what happens?
- 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!)
- pupil
- light enters the eye through an opening in the center of the iris called the pupil
- lens
- focuses light; adjustable
- cornea
- focuses light; not adjustable
- retina
- 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
- bipolar cells
- 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
- amacrine cells
- 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
- ganglion cells
- 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
- blind spot
- point at which optic nerve exits the eye and therefore contains no receptors at this point
- fovea
- 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
- macula
- greatest ability to resolve detail; center of retina
- ciliary muslces
- controls the lens;
- rods
- 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
- cones
- 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
- Why can you see a faint star in your periphery better than when looking directly at it
- 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
- trichromoatic theory of color vision
- 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
- Opponent-process theory
- 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;
- Retinex Theory
- 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
- Color constancy
- ability to recognize the color of an object despite changed in lighting
- Long wavelength cones
- responds well to red or yellow
- medium wavelength cones
- responds best to green, less to yellow
- short wavelength cones
- responds best to blue
- horizontal cells
- rods and cones make synaptic contact with horizontal cells and bipolar cells; horizontal make inhibitory contact wit bipolar
- optic chiasm
- 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
- lateral geniculate nucleus
- axons from ganglion cells go here; it's a nucleus of the thalamus specialized for visual perception
- optic nerve
- 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
- receptive field
- 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
- lateral inhibition
- reduction of activity in one neuron by activity in neighboring neuron
- parvocellular neurons
- 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
- magnocellular neurons
- 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
- koniocellular neurons
- 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
- visual pathway
- 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)
- primary visual cortex
- V1; responds to any kind of visual stimulus and is active even when we close our eyes and imagine visual stimuli
- secondary visual cortex
- V2; process info further and transmits to additional areas
- ventral stream
- visual paths in the temporal cortex, aka "what" pathway bc it is specialized for identifying and recognizing objects
- dorsal stream
- 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
- simple cells
- only found in primary visual cortex; receptive field of a simple cell has fixed excitatory and inhibitory zones
- complex cells
- 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
- end-stopped or hypercomplex cells
- resemble complex cells but it has a strong inhibitory area at one end of its bar shaped receptive field