Chapter 10: Auditory System

week 9

Sound stimulus

variations in air pressure traveling out from the source of the variations

INTERAURAL time difference

time it takes for sound to travel between the ears

super short in duration

how we can tell where a sound is coming from

sound waves

waves of pressure changes that occur in the air as a function of the vibration of a source

cycle

(in a sound wave)

the amount of time between one peak of high pressure and the next

pure tone

sound wave

changes in air pressure follow a sine wave pattern 

have 1 regular frequency

amplitude

difference between maximum and minimum sound pressures

loudness

perceptual experience of the amplitude or intensity of a sound stimulus

corresponds with pressure levels

decibel (dB)

physical unit that measures sound amplitude

frequency (sound stimulus)

the # of cycles that occur in a second

• shorter wavelength = higher frequency

pitch

the subjective experience of sound that is most closely associated w/ the frequency of a sound stimulus 

Hertz (Hz)

unit of measure indicating the number of cycles per second

• how many wavelengths pass in a second

• most humans are 20-20,000 hz

• highest sensitivity 2000-6000 bc of resonances in the outer and middle ear

Harmonics

higher frequencies present in a complex sound that are integer multiples of the fundamental frequency

complex sound

sound made of a mix of frequencies

fourier analysis

take a complex waveform and determine simpler waveforms that make up that complex pattern

—> simpler waves are sine waves

fundamental frequency

the lowest frequency in a complex sound

determines the perceived pitch 

timbre

perceived sound differences between sounds with the same pitch but different higher harmonics

SPECTRAL PROFILE

phase

position in one cycle of a wave

360 degrees in a single cycle

Pinna

collects sound and funnels it into the auditory canal

External auditory canal (meatus)

channel that conducts sound from pinna to tympanic membrane

tympanic membrane

thin elastic sheet that vibrates in response to sounds coming through the external auditory canal 

AKA EAR DRUMMMM 🥁🥁🥁🥁🥁

ossicles

3 little bones in the middle ear

malleus

1st ossicle

• gets vibes from tympanic membrane and transmits them to the incus

Incus

2nd ossicle

receives vibes from malleus and transmits them to the stapes

Stapes

3rd ossicle

gets vibes from incus and sends them to the oval window of the inner ear

eustachian tube

thin tube connects middle ear and pharynx

equalises air pressure on either side of the eardrum

tensor tympani

muscle connected to the malleus

stapedius

muscle connected to the stapes

acoustic reflex

reflex that tightens the tensor tympani and stapedius in response to chronic loud noise

cochlea

snail shaped in inner ear

has little hair cells that transduce sound into a neural signal

tympanic canal

1/3 chambers in the cochlea

separated from middle canal by basilar membrane

middle canal (cochlear duct)

1/3 chambers in cochlea

separated from tympanic canal by basilar membra

has the organ of corti

round window

soft tissue at the base of tympanic canal

• escape valve for excess pressure from loud sounds that arrive in the cochlea

reissners membrane

separates vestibular and middle canals

basilar membrane

separates tympanic canal from the middle canal

organ of corti lies on this

organ of corti

sits on the basilar membrane

houses hair cells that transduce sound into a neural signal

perilymph

fluid that fills the tympanic canal and vestibular canal

characteristic frequency

the frequency any location along the basilar membrane best responses to

hair cells

cells that have stereocilia for transducing the movement of the basilar membrane into a neural signal 

stereocilia

hairlike parts of the hair cells on top of the inner ear and outer hair cells

outer hair cells

sharpen and amplify responses of the inner hair cells

inner hair cells

cells that are responsible for transducing the neural signal

tectorial membrane

a membrane that rests above the hair cells within the organ of corti

place code theory

view that different locations along the basilar membrane respond to different frequencies

temporal code theory

view that frequency representation occurs because of a match between sound frequency and the firing rates of the auditory nerve

otosclerosis

inherited bone disease

• ossicles (stapes) calcify and are less conductive of sound

tinnitus

people perceive sounds (ringing) when none are present

• can be related to injury, age related hearing loss, can also be a cardio thing

hearing aids

amplify sound so that people with hearing deficits can hear sounds that would otherwise be below their thresholds

cochlear implants

stimulate auditory nerve with an electronic system

replacing job of the hair cells of the cochlea