PSYC110 Auditory System

what is sound?

sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid, or solid

what is the hearing range?

• human ear percieves frequencies between 20 Hz (lowest pitch) to 20 kHz (highest pitch)

• sounds beliw 20 Hz are infrasounds

• sounds above 20 kHz are ultrasounds

outer ear

sound is funneled via the pinna (external ear) through the ear canal to the tympanic membrace (eardrum), which vibrates the sound

middle ear/ear drum

consists of a small hollow region behind the tympanic membrane, contains bones that are set into vibration

innear ear

the cochlea is apart of the inner ear, it is filled with fluid and sounds transmitted through the air have to be transferred into its liquid medium (usually inefficient)

sound transduction

mechanoreceptors on the tips of the hair cells, movement towards the tallest cilia increases the firing rate of the cochlear nerve axon, while movement away from the tallest one decreases it

sound transduction pt 2

• the hair cells are the trigger point for a reaction to begin

• movement towards the tallest cilium opens the ion channels and increases the influx of K+ and Ca2+ ions

• movement toward the shortest cilium removes tension from the tip links, which permits the ion channels to close, stopping the influx

hair cells

they release the neurotransmitters onto the dendrites of the bipolar cells that make up the auditory nerve that goes to the brain

tympanic membrane

• membrane will vibrate every time

• pinna = carries sound to the T.M.

• cochlea = contains the auditory receptors, sound to the brain

• ear canal = outer ear

basilar membrane

• tuned to respond to different frequencies of sound

• hearing range

• detect high and low pitch

sound localization

• loudness

• latency/time difference of 0.66 milliseconds for sound to get from one ear to the other

• if signal reaches both ears simultaneously, neurons in the middle of the array will fire

• if signal reaches one ear before the other, the neurons farther away from the ‘early’ ear will be stimulated

sensorineural hearing loss

from the cochlear and more neural, fewer hair cells, turn up volume more, get more bending of the remaining hair cells (hair cells are destroyed by the time one notices hearing loss)

repair for hearing loss

Hearing aid

• A device applied to the outer ear to amplify sound to improve hearing

Cochlear implant

• A device surgically implanted in the inner ear that enables a deaf person to hear sounds

• Decomposes the pitch

• Finds out what sound it is

• Conveys to the auditory nerve

• Needs to be surgically implanted under the age of 3 in order for them to have full recovery and hearing range

• Critical period, it will adapt at these crucial times