How hear pitch?

n Frequency theory – entire membrane vibrates in synchrony with sound wave, like eardrum

q 500 hz tone, neuron fires 500/sec

q However can’t fire more than 1000/sec

n Volley principle – fire in a staggered fashion

n Phase locking – inner hair cells excit when bend one way, inhib when bend other

n Best for low tones (up to 4k hz)

Pitch Perception

n Place theory – based on location on basilar membrane

n Narrow and stiff at base (near stapes), wider and thinner at apex

n Traveling wave – maximum displacement – diff pitches peak at diff locations (higher pitches closer to stapes)

n Auditory nerve fibers – frequency tuning curves – each has char. frequency

Pitch and loudness

n As loudness increase, range of pitches that neuron responds to increases, peaks at 60-80 db – loudness – no. of neurons firing as well as no of times neuron fires.

n Equal loudness contour - how intense does each pitch need to be so all sounds are equally as loud? Diff sensitivities over different freq

n Louder gets, flattens curve, less likely to distinguish pitch because affecting larger part of basilar membrane