Further observations concerned with auditory fatigue during vocal and nonvocal speech activities.

Abstract

Eleven female subject, with normal hearing sensitivity were exposed to 90 dB SL 2000- and 4000-Hz fatigue stimuli for 3 min; temporary threshold shifts (TTS) were measured one-half octave above the fatigue frequency. Over several experimental sessions separated by at least 24 h, each subject performed each of the following tasks during the exposure time for each fatigue frequency: Reading a passage aloud (RA); Reading a passage silently (RS); Reading a passage silently while articulating the words without voicing or whispering (RSA); Reverie which involved no reading (REV). The RA task produced significantly greater TTS than the other task conditions when the fatigue frequency was 4000 Hz, implying that transmission of the fatigue stimulus was enhanced, perhaps owing to impedance changes resulting from contraction of the middle-ear muscles during speech production. The RA-task condition produced consistently, but not significantly, less TTS than the other task conditions when the fatigue stimulus was 2000 Hz, which might indicate that transmission of the fatigue stimulus was being slightly attenuated during speech production. The data are discussed in terms of a hypothesis indicating that speech production alters the impedance of the auditory system, hence altering the transmission of sound. A TTS paradigm incorporating speech activities may be an indirect but useful method for assessing the sound transmission properties of the human auditory system.