ch 9 - hearing: physiology and psychoacoustics

sound wave

fluctuations in air pressure across time, caused by vibrations of objects in the environment

amplitude

the intensity or magnitude of displacement of a pressure wave

decibels

physical intensity of sound

loudness

perceived intensity

range of human hearing

0-130 db, 20-20,000 hz

high intensity means

louder sound

low intensity means

softer sound

frequency

the number of times per second that a pattern of pressure change repeats

hertz

frequency of sound (1 Hz = 1 cycle/sec)

pitch

perceived frequency

what makes up white noise

all audible frequencies in equal amounts

audibility threshold

the lowest sound pressure level that can be reliably detected at a given frequency

outer ear

external portion of the ear, collects and focuses sound waves

outer ear contains

pinna, ear canal

pinna

outer, funnel-like part

ear canal

canal that conducts sound vibrations from the pinna to the tympanic membrane

tympanic membrane

eardrum at the end of the ear canal, vibrates in response to sound

middle ear

transfers and amplifies sound vibrations from the tympanic membrane to the oval window

ossicles

three tiny bones: malleus, incus, stapes

malleus

recieves vibration from tympanic membrane

incus

connects malleus to stapes

stapes

transmits sound to oval window

oval window

flexible opening to cochlea through which the stapes transmits vibration to the fluid inside

inner ear

converts sound vibrations into neural signals

cochlea

tiny, coiled structure where sound is transduced in the organ of Corti to the auditory nerve

auditory nerve

a collection of neurons that convey information from hair cells in the cochlea to the brainstem

hair cell

a cell that transduces mechanical movement in the inner ear into neural activity sent to the brain

organ of Corti

a structure on the basilar membrane that is composed of hair cells and dendrites of auditory nerve fibers

basilar membrane

a plate of fibers that forms the base of the cochlea

stereocilia

hairlike extensions on tips of hair cells that initiate the release of neurotransmitters when bent

place code

information about a sound wave’s frequency is coded by the place along the cochlea that has the greatest mechanical movement

place code of high frequency

base, near oval window

place code of low frequency

apex, at the end

temporal code

information about a sound wave’s frequency is coded by the timing of neural firing as it relates to the period of the sound

temporal code high frequency

fast firing

temporal code low frequency

slow firing

neural pathway

ear, cochlear nuclei, superior olive, inferior colliculus, medial geniculate nucleus, cortex

cochlear nuclei

first brainstem nucleus at which auditory nerve synapses

superior olive

brainstem region where inputs from both ears converge

inferior colliculus

midbrain nucleus in the auditory pathway mostly from contralateral ear

medial geniculate nucleus

part of the thalamus that relays auditory signal to the temporal cortex

primary auditory cortex

A1, in temporal lobe, basic acoustic information

secondary auditory cortex

A2, adjacent to A1, responds to more complex characteristics of sounds

tonotonic organization

neurons are organized anatomically in order of frequency

conductive hearing loss

hearing loss caused by problems with the outer or middle ear

how to fix conductive hearing loss

hearing aids

what is the problem of conductive hearing loss

amplification of sound

sensorineural hearing loss

hearing loss caused by defects in the cochlea or auditory

problem of sensorineural hearing loss

transduction of sound

how to fix sensorineural hearing loss

cochlear implants

presbycusis

normal, age related hearing loss

what does presbycusis affect

high frequency, low amplitude

other external factors of hearing loss

obstruction of ear canal, ear infection, excessive noise exposure