Chapter 6

Chapter 6 - Chapter 6- The Auditory System: Perceptual...

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Chapter 6- The Auditory System: Perceptual Aspects of Hearing A. Intensity and Loudness Audibility thresholds Procedural aspects: - 2 general procedures are used to deliver sound stimuli: o (1) Open-ear method: sound is delivered by a loudspeaker located directly in front of the subject in an enclosed room; absolute threshold values obtained by this method are called minimum audible field (MAF) thresholds. PRO: obtained by free-field measurement; represent a natural way of listening. CON: head position + environmental quality of the room can affect sound detection. o (2) Closed-ear method: sound delivered through earphones; sound pressure at the eardrum is estimated or measured directly through a detailed calibration process. Absolute thresholds obtained in this way = minimum audible pressure (MAP) thresholds. PRO: MAP thresholds can be related to exact pressure values at the eardrum; it is also easier to ensure sound is equally applied to both ears. CON: individual differences in size/shape of ear canal mean that pressures exerted upon the eardrum will not necessarily be the same among people. - General procedures used to determine absolute thresholds can be based on Fechner’s classical methods; sound may be presented by open or closed ear methods; data can be shown on a psychometric function of detection performance and intensity. - Typically, sound intensity that produces 50% detection level is chosen as the criterion. Absolute detection thresholds: - Hearing sensitivity is very much dependent on frequency. - A tone of 1500 Hz requires low intensity (~5 dB) to reach 50% detection performance. - A tone of 50 Hz on the other hand has a very high threshold, ~45 dB-SPL. - Minimal audibility curve: psychophysical function showing the relationship between absolute detection threshold and frequency. - Lowest detection thresholds are found in range of 2000-4000 Hz (“middle frequencies”). - Sounds at frequencies below this optimal range have progressively higher thresholds. - The lowest frequency that can be heard = btw 10-20 Hz. - Sounds at frequencies higher than the optimal range also have gradually higher thresholds. Anatomical and physiological determinants of the minimal audibility curve: - Possible factors responsible for this U-shaped profile can be divided into 3 sources: o (1) Conductive elements of the outer and middle ear o (2) Mechanical response function of the cochlea o (3) Physiological properties of the auditory nervous system - Cochlear source can be eliminated: its mechanical response function is largely similar across a broad range of frequencies. - The resonant properties of the pinna/auditory canal maximally enhance sound at middle frequencies; this largely accounts for the low threshold values in this middle range. -
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This note was uploaded on 12/18/2011 for the course PSYC 212 taught by Professor Shahin during the Fall '11 term at McGill.

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Chapter 6 - Chapter 6- The Auditory System: Perceptual...

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