Changes in TTS associated with humming and nonvocal activities.

Abstract

This investigation studies the effect of humming and of certain nonvocal activities on TTS (temporary threshold shifts) from a 5-min 500-Hz 118-dB SPL exposure. The experimental technique consisted of measuring hearing thresholds at 700 Hz before and after exposure, this exposure being accompanied by the performance of a specific activity such as humming. Analysis of the results indicates that TTS from the exposure accompanied by humming was significantly less than TTS from exposure without any supplementary activity. The following conditions were tested: (1) humming at 125 Hz (males) or 250 Hz (females); (2) humming loudly at the same frequencies; (3) humming at 250 Hz (males) or 500 Hz (females). TTS in cases (2) and (3) was consistently less than TTS in case (1). Repeatedly turning the head during exposure, an activity believed to elicit middle-ear muscle contraction, resulted in less TTS than no activity during exposure. Listening to recorded humming during exposure did not significantly alter TTS from the exposure, nor did the activity of exhaling after preparing to hum. Attenuation provided by middle-ear muscle contraction during phonation does not appear sufficient to decrease TTS to the extent that humming does. Sound may be attenuated by inefficient stapes vibration during phonation and TTS may thus be reduced. Two other possibilities are discussed that could account for the TTS decrease: interference between humming and the exposure tone; and interference (by humming) with the central control of middle-ear muscle activity.