sensation/perception exam 2

major components of outer ear

auricle, helix, lobule, external acoustic meatus

major components of middle ear

tympanic membrane, malleus, incus, stapes,

major components of inner ear

semicircular canals, cochlea, maculae

what membrane separates middle ear from outer and inner?

tympanic membrane

frequency

corresponds to pitch, Hertz (Hz)

amplitude

corresponds to loudness/intensity, Decibels (dB)

fourier analysis

complex sounds broken down into their “pure tone” components

fourier synthesis

complex sound can be created by adding “pure tone” components

psychoacoustics

study of psychological correlates of physical dimensions and acoustics

energy does not equal perception

purpose of the pinna

capture sound waves to direct to inner ear, sound localization

function of the ossicles

collect and amplify sound waves from tympanic membrane, joints in between shake, send vibration to cochlea

ossicles

malleus, incus, stapes

how are sound waves visualized

waveforms, spectrogram, spectrum

differences in sound waves

waveform: pressure changes over time

spectrogram: plot a spectrum over time

spectrum: plot of amplitude vs. frequency

muscles of middle ear

tensor tympani and stapedius

acoustic reflex

muscles tense with loud sends and self-generate sounds such as chewing and swallowing

anatomy of cochlea

3 canals, vestibular canal, cochlear duct, tympanic canal

membranes separating layers of cochlea

between vestibular and cochlear: Reissner’s (vestibular) membrane

between cochlear and tympanic: basilar membrane

oval window

where stapes connects to cochlea, vibrations push stapes to oval window, transmits pressure into fluid

round window

pressure release in ear, bulges out in response to sound waves

helicotrema

located at apex of cochlea, connects vestibular and tympanic membrane, pressure equalization and low-frequency sound transmission

what makes up cochlear partition

tectorial membrane, organ of Corti, basilar membrane

inner hair cells

1 row, afferent

arranged front to back, shortest to longest

most auditory info (90-95% of audio info)

outer hair cells

3 rows, mainly efferent innervation

stereocilia on top of OHCs in V or W shape

improve sensitivity and frequency selectively

what happens in cell when hair cells are stimulated

stereocilia bend due to fluid movement

gated ion-channels open

potassium rushes in from surrounding endolymph, hair cell depolarizes

calcium enters, releases NTs

NTs stimulate auditory nerve, sending information to the brain

does stimulation of hair cell lead to action potential

no, but they produce graded receptor potential

equal loudness curves

frequency vs. loudness of sound

ears are most sensitive between 2-4 kHz

low and high frequencies have to be much louder than midrange

why does frequency not equal pitch

can discriminate between 1 Hz difference

500 > 1000 Hz is bigger change than 5000 > 5500, 100% vs. 10% difference

why does decibels not equal loudness

we are sensitive to changes in loudness, can discriminate changes of less than 1 dB

intensity leads to more action potentials and more action potentials are generally interpreted as higher volume

response comprehension

how we perceive and interpret loudness

amplitude coding in cochlea

rate of hair cell depolarization

firing rate of auditory nerve fibers

number of hair cells activated

frequency coding in cochlea

place coding and frequency matching

place code

different frequencies displace different regions of cochlear partition

higher frequencies: closer to base (more accurate)

lower frequencies: closer to apex

frequency matching

phase locking and volley principal

phase locking

each AN fiber fires at particular point in sound wave

works for low frequency, fiber can only fire so fast

volley principal

multiple auditory nerves divide and conquer high frequency sounds

each neuron locks on particular part of sound wave

2-tone suppression

two sounds of different frequencies enter ear, one tone can suppress vibration of basilar membrane

helps cochlea sharpen frequency selectivity

rate saturation

limit of how fast an auditory neuron can fire in response to increasing sound intensity

once saturation is reached, firing rate is peaked and cannot get faster

how many auditory nerves innervate a single hair cell

IHC: Many:1

OHC: 1:Many

characteristic frequency

each IHC and ANF has characteristic frequency based on its location on basilar membrane

base responds to higher frequencies, apex responds to lower frequencies

aspects of stimulus affecting rate of firing on auditory nerve

amplitude, frequency, duration

labeled-line coding

cross-fiber patterning

each ANF is tuned to specific characteristic frequency

brain interprets identity of active neuron to determine frequency of the sound

why is labeled-line coding better at telling us frequency of quiet sounds than loud sounds

as only a few ANF’s respond, they tune closes to the sound’s frequency

at high sounds, many fibers respond, incuding those tuned to nearby frequencies

spiral ganglion

transmits electrical signals from IHCs to cochlear nucleus in brainstem

type I neurons

myelinated, innervate 1 IHC

type II neurons

non-myelinated, connect to multiple OHCs

brain structures involved in auditory pathway in order

pinna, IHC, spiral ganglion, cochlear nucleus, olives, inferior colliculus, medial geniculate nucleus, A1, A2, association cortex

why is the superior olive a good place for sound localization to occur

first point where brain compares input from both ears, allows it to detect tiny differences in timing and loudness

what is the auditory cortex

part of the brain responsible for processing sound information

where is the auditory cortex

temporal lobe, superior temporal gyrus

primary auditory cortex

any sound elicits activity, bilateral activation

secondary auditory cortex

more complex sounds elicit activity

association cortex

more complex sounds elicit activity, also processes other sensory information

tonotopic organization

base of cochlea responds to high frequencies, apex responds to low frequencies

in temporal lobe, each area corresponds to a different frequency spot in cochlea

Broca’s area

in frontal lobe, important for motor speech production

Broca’s aphasia

“broken speech”

non-fluent aphasia, difficulty with motor production, speak slowly and inarticulately

trouble with writing and gestures

Wernicke’s area

in temporal lobe, important for language comprehension

Wernicke’s aphasia

“word salad”

fluent aphasia, smooth, but nonsense speech

impaired ability to remember names of objects, difficulty finding right word

parts of the brain important for language processing

Broca’s area, Wernicke’s area, A1, A2

difference between left and right hemispheres for language/speech processing

language is usually in left hemisphere, lateraliized

how things are said in right hemisphere, emotion

Jeffress model of sound localization

how the brain localizes sound using ITDs to explain differences in the time a sound takes to arrive at each ear

ex: sounds arriving at right ear first will activate right leading neurons first, then signal from left will activate same neuron

what brain region does interaural time difference

medial superior olive

interaural time difference (ITD)

difference in time it takes for sound to reach each ear

works best in low frequencies below 1500 Hz

helps us determine which side a sound is originating from

how do we determine interaural level difference

based on intensity of sound reaching ear (how loud)

helps ears localize sounds for high frequencies (above 1500 Hz)

what brain region determines interaural level difference

lateral superior olive

why is interaural level difference different from front to back

head shadowing, one side blocking sound waves from the other

cones of confusion

3D surfaces around head wehre sounds produce same ITD and ILD

use pinna spectral cues, head movement, and other cues

how does the pinna help with localizing sounds

funnels sound energy into the ear canal, better at funneling some frequencies over others

direct transfer function (DTF)

function that describes how the pinna, ear canal, head, and torso change intensity of sounds with different frequencies

are all frequencies funneled to the eardrum equally

no, depends on pinna and ear canal shapes

certain frequencies get amplifed (2000-5000 Hz)

methods of distance perception

relative intensity of sound

spectral composition of sounds

relative amount of direct energy vs. reverbant energy

conductive hearing loss

caused by problems with ossicles

ex: ear infections, otitis media

otosclerosis

abnormal growth of middle ear bones, can be fixed by surgery

sensorineural hearing loss

most common

defects in cochlea and auditory nerve, hair cells are injured

result of antibiotics or cancer drugs

natural consequences of aging

young people: 20-20000 Hz

college age: 20-15000 Hz

cochlear implants

flexible coils with miniature electrode contacts

signals activate electrode to appropriate positions along cochlear implant