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how hearing works
vibration of ossicles against oval window causes waves in basilar membrane, hair cells bend causing impulse and neurotransmitters released by hair cells act upon auditory neurons
membrane at the far end of middle ear, smaller area than tympanic membrane so pressure funneled
tiny hairs that protrude from each hair cell into inner duct and abut against tectorial membrane
deafness that occurs when ossicles in the middle ear become rigid and cannot carry sounds inward from tympanic membrane to cochlea
what can people with conduction deafness hear?
vibrations that reach cochlea by routes other than middle ear
conventional hearing aid is
a device that magnifies sound pressure sufficiently for vibrations to be conducted by other bones on the face into the cochlea
cochlear implant is
a device that performs the transduction task normally done by the ear's hair cells by translating sounds into electrical impulses and sending impulses through wires permanently implanted into cochlea where they stimulate terminals of auditory neurons
when can cochlear implant be used
when deafness results from destruction of hair cells, not when auditory nerve has been destroyed
bekesy's hypothesis about hearing
rapid rifing in neurons that come from proximal end of membrane accompanied by little or no firing in neurons from more distal parts is interpreted as high pitched sounds; rapid firing neurons from more distal portion of membrane interpreted as lower pitched sounds
asymmetry of auditory masking
low frequency sounds mask high frequency sounds much more easily than high frequency sounds mask low frequency sounds
pattern of hearing loss with age
sensitivity to high frequency lost to a much greater degree than low frequencys with age
why does hearing change with age?
because of wearing out of hair cells with repeated use (coding for high frequencys acted upon by all sounds, low frequency hairs only acted on by low frequency sounds)
for relatively low frequencies, percieved pitch depends on
which part of basilar membrane is maximallhy active and the timing of that activity (ie frequency of action potentials)
auditory sensory neurons send their output where
to nuclei in the brainstem which sends axons to primary auditory area of cerebral cortex
high-frequency tones activate neurons on one end of cortex, low-frequency tones activate neurons on other end
what determines the specific amount of cortex that is devoted to any particular range of frequencies
area of the parietal lobe of the cortex which receives input from the primary auditory cortex; involved with music perception and visual space perception
sound localization depends on
the time at which each sound wave reaches one ear compared to the other
how are words identified?
from patterns in change of frequency and amplitude that occur over time as the word is spoken
an illusion in which people hear phonemes that have been deleted from words or sentences as if they were still there
what determines which sound is heard in phonemic restoration
the surrounding phonemes and meaningful words and phrases that they produce
how do auditory neurons vary
some have higher thresholds than others; brain uses info about pattern of impulses to perceive loudness; different auditory neurons respond to different differences in time sound received
specialized light-detecting cells that evolved and became connected to animal's nervous system
how does lens shape change
becomes more spherical when focusing on objects close to eye, flatter when focusing on those farther away
process by which a stimulus from the environment generates electrical changes in neurons, done by photoreceptor cells
pinhead-size area of hte retina that is in teh most direct line of sight, specialized for high visual acuity
aka bright light vision or photopic vision; specialized for high acuity and color perception
aka dim-light vision or scotopic vision; specialized for sensitivity (ability to see in dim light)
the more rapid decrease in sensitivity that occurs after you turn on a bright lamp or step out into sunlight
how does bright light make rods nonfunctional
light causes rhodopsin to break down into two inactive substances
how does convergence vary between rods and cones
rods have lots of convergence, cones have little or no convergence
subtractive color mizing
the mixing of pigments; pigments create color by subtracting (absorbing) some of the light waves that would otherwise be reflected to the eye
three primaries law
different wavelengths of light can be used to match any color that the eye can see if they are mixed in the appropriate proportions
any three wavelengths as long as one is from the long-wave end of spectrum, one from short-wave end, and one from middle
law of complementarity
pairs of wavelengths can be found that, when added together, produce the visual sensation of white
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