Characteristics of the acoustic reflex in response to narrow bands of noise.

Normal-hearing young adults (5 M, 6 F) were exposed monaurally for 3 min to narrow-band noises centered at .5, 1, and 4 kc/s, at 20 db above respective acoustic reflex (AR) thresholds. Strip-chart recordings (1 mm/sec) of middle-ear muscle contractions were graphed and evaluated for peak amplitude, latency, adaptation, and recovery from contraction. The relative AR amplitude was greatest to the .5-kc/s band and decreased with increasing stimulus frequency. Women exhibited greater AR than men in response to the lowest frequency of stimulation. The AR latency was significantly faster for the .5-kc/s band, with no sex difference. AR adaptation increased with increasing stimulus frequency and markedly so for women in response to the mid- and high-frequency bands; but for men at all frequencies there was AR enhancement even after 3 min of stimulation. Finally, there were no significant overall differences in AR relaxation time either for men or women, though there was a significant sex by frequency interaction such that at 4 kc/s men's recovery was faster. Implications of these results were discussed relative to the research data on sex differences in TTS at different frequencies.