Why study “sound”?
- “Blindness deprives you of contact with things; deafness deprives you of contact with
– Helen Keller
What is sound?
- Wave resulting from compressions of particles
- Amplitude represents intensity of sound (measured in dB as sound pressure) and
perceived by us as loudness (but note that amplitude is not the only determinant of
- Frequency is the cycles of sound per second and perceived as pitch
- Pinna = structure of flesh and cartilage attached to each side of the head that alters the
reflections of sound waves and helps us locate the source of a sound
- Malleus, incus, and stapes (A.K.A. hammer, anvil, & stirrup)
- Helps to attenuate the sounds we make ourselves
- People with damage to middle ear complain that inner sounds (e.g. swallowing) are
- Cochlear is about 4 mm in diameter
- For the basilar membrane, it is 5 times wider at the apex than at the base
- People can normally detect pitch difference of about 2 Hz to 2000 Hz
- Place Theory
o We discriminate pitch based on where the sound causes maximal displacement
of the basilar membrane.
o Potential problem: the basilar membrane is coiled up in the cochlear, so are we
really detect the miniscule displacement in the coiled form? - Frequency Theory
o Vibration rate of auditory nerve cell is identical to frequency of sound waves.
o Potential problem: A single nerve cell can only fire up to about 1000 action
potentials, yet we can detect sound up to 2000 Hz.
- Volley principle
o When there is a sound wave that is at a higher frequency, several neurons are
activated and they fire action potentials out of phase with one another so that
when combined, a greater frequency of sound can be encoded.
- At low frequency or pitch (e.g. 100 Hz), frequency theory is applicable.
- At high frequency or pitch (e.g. 4000 Hz), volley theory is applicable.
- At very high frequency or pitch (e.g. 20000 Hz), place theory is applicable.
- We determine the direction and distance of a sound by comparing the responses of our
o Binaural difference in loudness of sound
o Binaural difference in hearing onset of sound
o Binaural difference in phase of sound waves
- We don’t consci