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PSYC 260 (11)
Julia Kam (11)

Part I - Lectures 5 & 7.doc

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University of British Columbia
PSYC 260
Julia Kam

Audition Why study “sound”? - “Blindness deprives you of contact with things; deafness deprives you of contact with people.” – 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 loudness) - Frequency is the cycles of sound per second and perceived as pitch Outer ear - 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 Middle ear - 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 annoyingly loud Inner ear - Cochlear is about 4 mm in diameter - For the basilar membrane, it is 5 times wider at the apex than at the base Pitch Discrimination - 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. Sound Localization - We determine the direction and distance of a sound by comparing the responses of our two ears. 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
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