11 Auditory

11 Auditory - AUDITION AC Brown page 1 A7b INTRODUCTION...

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Unformatted text preview: AUDITION AC Brown page 1 A7b INTRODUCTION Terms: external auditory canal = external auditory meatus eardrum = tympanic membrane auditory tube = Eustatian tube A. Transducer Function of Ear: to convert sound (pressure) waves in the range 20 - 20,000 hz (hertz, cycles/second) into action an action potential pattern that permits sensation of the incident sound and a recognition of its parameters B. Psychophysics of Sound 1. Sound parameters Physical Unit Physiological Frequency Hertz (hz, cycles/second) Pitch Power (or amplitude) bel or decibel (db) Loudness Shape of wave harmonic content (freq. spectrum) Timbre Note: pure tone = sine wave AUDITION AC Brown page 2 A7b INTRODUCTION (continued) B. Psychophysics of Sound (continued) 2. Units of Power/Loudness/Intensity: decibels (db) Note: when two sound sources are present simultaneously, the louder tends to mask (suppress perception of) the softer 3. Audibility Curve: the auditory system is most sensitive at the midrange of frequencies (500-3000 hz) and progressively less sensitive at higher and lower frequencies 4. Audiogram: Hearing threshold compared to normal as a function of frequency a. determined by measuring hearing threshold compared to normal at several frequencies b. on an audiogram, normal sensitivity at a given frequency is plotted as 0 db; degree of hearing loss at each frequency is noted by the distance below the 0 db line c. each ear is tested separately AUDITION AC Brown page 3 A7b AUDITORY SYSTEM SOUND TRANSMISSION A. Sequence for Sound Wave Transmission 1. Collection of sound waves in the external ear canal (external auditory meatus); concentrates sound waves 2. Vibration of the tympanic membrane (ear drum) a. large area (relatively) so helps to amplify sound b. transmits sound vibrations to middle ear ossicles 3. Conduction by ossicles through middle ear a. ossicular function: sound transmission from tympanic membrane to oval window of the cochlea b. middle ear muscles (tensor tympani and stapedius): muscle contraction decreases efficiency of ossicular sound transmission function: protect against cochlear damage due to excess sound energy; tympanic reflex loud sound muscle contraction Note: cannot protect against very loud sound or sound of sudden...
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This note was uploaded on 01/03/2012 for the course BIO 308 taught by Professor Acbrown during the Spring '10 term at Portland.

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11 Auditory - AUDITION AC Brown page 1 A7b INTRODUCTION...

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