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Lecture 4

PSYC 212 Lecture 4: Chapter 9 – lecture 4

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McGill University
PSYC 212
Mathieu Roy

Chapter 9 – lecture 4  Sound waves o Sound comes from pressure fluctuations in the air o Amplitude = intensity = loudness = energy  Measure in decibels (ratio btwn 2 sound pressures)  dB = 20log (pressure/pressureo)  Amplitude correlates to loudness, air pressure  Measured in decibles  Use minimum audible sound as reference pt )the hearing threshold)  Intensity is the square of pressure o Propagate in 3d. intensity corresponds to the energy of the sound wave when it hits a 2surrface like an eardrum o Frequency = pitch  Measured in hertz (cycles/sec)  Wavelength correlates to pitch  Period: time taken to complete one cycle (a wavelength)  Frequency: cycles per second o Sine wave = pure tone o Complex sounds are spectra displaying energy present at multiple frequencies  Complex sounds: combination of several frequencies, described by their spectra  Many sounds have harmonic spectra o Harmonic spectra st  1 harmonic/fundamental frequency: lowest frequency component of the sound  Other harmonics: have frequencies that are integer multiples of the fundamental  Timbre: quality of sound  Harmonic: each frequency component  1 harmonic/fundamental frequency: lowest-frequency, determines the pitch perceived  other harmonics are simple integer multiples of the fundamental  harmonic sounds generally come from a single source and sound nice  timbre is quality, given by harmonics  missing fundamental: perceived pitch is the same even if the fundamental is not there  the harmonics added together create the same frequency  Basic structure of the Mammalian Auditory System o Outer ear: external sound-gathering portion of the ear  Pinna: outer, funnel-like part of the ear  Ear canal: conducts sound vibrations from the pinna to the tympanic membrane and prevents damage tot eh tympanic membrane  Tympanic membrane: ear drum, vibrates in response to sound o Middle ear: air-filled chamber that amplifies vibration from the tympanic membrane to the oval window  Ossicles: malleus, incus, stapes  Oval window: flexible opening to cochlea from which the stapes transmits vibration tot eh fluid inside  Tensor tympani: muscle attached to the malleus sensing the tensor tympani decreases vibration  Stapedius: muscles attatched to the stapes, tensing the stapedius decreases vibration  Acoustic reflex: protects the ear from intense sounds via contraction of the stapedius and tensor tympani o Inner ear: hollow cavity in the temporal bone of the skull  Cochlea: spiral structure containing the Corti  Tympanic, vestibular, middle: fluid filled canals  Helicotrema: opening that connects the tympanic and vestibular canals at the apex of the cochlea  Reissner’s membrane: tissue separating vestibular and middle canal  Basilar membrane: fibers that separate middle and tympanic canals  Cochlear partition: basilar membrane, tectorial membrane, Corti, responsible for transduction of sound waves into neural signals  Round window: releases excess pressure remaining from extremely intense sounds  Corti: hair cells and dendrites of auditory nerve fibers  Stereocilium: hairlike extensions on the tipsof hair cells that initiate the release of neurotransmitters  Tectorial membrane: gelatinous structure floating about inner hair cells and touching outer hair cells  Tip link: filaments that stretches from the tip of a stereocilium to the side of its neighbor  Coding of amplitude and frequency in the cochlea  Place code: tuning of dif parts of the cochlea to dif frequencies in which info about the particular frequency of an incoming sound wave is coded by the place along the cochlear partition that has the greatest mechanical deisplacement  Afferent fiber: neuron that carries sensory info to the central nervous system  Efferent fiber: neuron that carries info from the CNS to the periphery o Auditory nerve  Threshold tuning curve: graph plotting the thresholds of a neuron or fiber in response to sine waves with varying frequencies at the lowest intensity that will give rise to a response  Characteristic frequency (CF): frequency to which a particular auditory nerve fiber is mo
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