Auditory system Flashcards
what are the 2 measures of sound
frequency and sound pressure level
sound frequency
pitch; how rapidly wave cycles (crest to crest)
sound pressure level
measures magnitude of pressure fluctuations; loudness of sound
how is intensity of sound measures
amplitude of sound wave
3 main cues to localize sounds
interaural time difference, interaural level difference and head-related transfer function
interaural time difference
difference in time taken for a sound to reach each ear; incorporate from both ears (binaural cues)
when is ITD greatest
when sound is 90 degrees (directly towards one ear)
head-related transfer function
specifies how the body influences sound (body scatters) and provides vertical location cues based on changes in frequency spectrum
interaural level difference
difference between sound pressure level at each ear
sound shadow
obstacle casts by the head that lowers intensity of sound at ear furthest from stimuli
when is ILD useful
high frequency sounds (ILD smaller is frequency decreases)
what parts of the body influence how sound reaches inner ear; head related transfer function (HRTF)
pinna, head, torso
spectral analysis
analyzing frequency content of a sound
what cues are useful for low frequency sounds
interaural time difference (ITD)
what cues are useful for high frequency sounds
interaural level difference (ILD)
what are ILD and ITD useful for
localizing horizontal location of sound (incorporates info from both ears)
what are the 3 bones in the middle ear
ossicles: malleus, incus, stapes
how do sound waves enter the inner ear
tympanic membrane ->ossicle bones -> oval window
cochlear fluids
-perilymph (low K+ conc) in scala tympani and scala vestibuli
-Endolymph (high K+ conc) in scala media
basilar membrane
moves up and down with sound via fluid movement
inner hair cells
transmit information to the brain; connected to basilar membrane
outer hair cells
amplify movement of basilar membrane; connected to tectorial membrane
tectorial membrane
membrane attached to tip of tallest stereocilia in outer hair cells; helps with hearing by stimulating hair cells and supporting traveling wave
base of cochlea
narrow and stiff
apex of cochlea
wide and floppy
what part of the cochlea moves for high frequency sounds
base
what part of the cochlea moves for low frequency sounds
apex
how many rows of inner and outer hair cells are in the ear
1 row of inner hair cells and 3 rows of outer hair cells
kinocilium
tallest hair in hair bundle
hair bundle
slanted bundle of stereocilia on hair cell
when do hair cells depolarize
stereocilia deflect towards kinocilium
when do hair cells hyperpolarize
stereocilia deflect away from kinocilium
hair cell action potential mechanism
K+ increase depolarizes hair cell -> Ca2+ channels open -> glutamate response -> action potential to ganglion cells -> auditory nerve
characteristic frequency/ best frequency
the frequency where the spiral ganglion cells responds to the most
auditory nerve response: phase locking
neurons fire action potentials at a particular phase of sound wave which provides frequency information
when does phase locking occur
at low frequencies (under 4,000 Hz)
how is frequency information obtained for high frequencies (over 4,000 Hz)
tonotopic arrangement of auditory nerve fibers
superior olive
earliest area sensitive to binaural cues
where are ITD encoded
medial superior olive
where are ILD encoded
lateral superior olive
mechanism for ILD and ITD encoding in superior olive
activity in 1 ear initiates activity and sends info to superior olive, initiates activity in right ear, signals for both years meet at a neuron
pathway from inner ear to auditory cortex
cochlea, spiral ganglion, auditory nerve, dorsal/ventral cochlear nucleus
ventral cochlear nucleus(timing info) -> superior olive
dorsal cochlear nucleus (HRTF) -> inferior colliculus
MGN in thalamus -> auditory cortex
where is the auditory cortex in humans
dorsal and lateral superior temporal gyrus
what are the 3 subsections of the auditory cortex
core, belt, and parabelt
what are the 3 tonotopic areas in the core of the auditory cortex
primary auditory cortex (A1), rostral field (R), rostral temporal field (RT)
how is the core of the auditory cortex organized
tonotopically; orderly arrangement of neurons in terms of characteristic frequency/ best frequency
tonotopic organization of belt and parabelt
belt: some tonotopic organization
parabelt: not well organized (tonotopically)
what does the parabelt region interpret
speech patterns (not tonotopically organized)
subsections of auditory cortex hierarchy (low -> high)
core, belt, parabelt
harmonics
multiple frequencies that constitute sound
harmonic complex tones (HCT)
sound composed of multiple frequencies where each frequency is an integer multiple of a fundamental frequency (F0)
what class of sound does the core respond best to
pure tones (single frequency)
what class of sound does the belt respond best to
band-passed noise (intermediate complexity)
what class of sound does the parabelt respond best to
species specific vocalization/ speech and vowel sounds (complex sounds)
ventral pathway from auditory information
what the sound is; core -> belt regions -> inferior frontal cortex
dorsal pathway for auditory information
where sound is and how to interact with it;
auditory cortex -> parietal cortex (intraparietal lobule) -> frontal cortex (premotor cortex)
how does change from non behaviorally relevant info to behaviorally relevant info impact action potential
increase in neuron firing
how does change from one behaviorally relevant info to another behaviorally relevant info impact action potential
no significant change in action potentials
how does the ventral pathway assign sounds categories
different neurons respond to different sounds/ phonemes
*morphed word monkey study
where in the brain processes phonemes
superior temporal gyrus
*different neurons respond to different phonemes
what speech does posterior superior temporal gyrus represent
fast varying speech sounds (phonemes)
what speech does antierior superior temporal gyrus represent
slow varying speech sounds (ex. rhythm of speech)
what speech does middle superior temporal gyrus represent
medial time scale sounds (ex. syllables)
