Individual, sex, and ear differences in measures of overshoot and psychophysical two-tone suppression

Abstract

Notched-noise overshoot and two-tone suppression were measured at 1000 Hz using standard procedures in 40 normal-hearing, psychoacoustically naive adults, counterbalanced for sex and listening ear. The threshold variability across listeners for the same condition often exceeded 30 dB. In the overshoot conditions, the signal was an average of 7 dB harder to detect when it was presented at the onset of a 500-ms masker (masker notch width: 1000 Hz) than when signal onset was delayed by 400 ms. Across listeners, this overshoot effect ranged from 1 to 17 dB. In the suppression conditions, for some listeners, the forward-masked signal was as much as 15 dB easier to detect when the tonal on-frequency masker (1000 Hz) and suppressor (1150 Hz) were presented together, than when the masker was presented alone, indicating suppression. For other listeners, however, presenting the masker and suppressor together increased thresholds by as much as 13 dB, indicating additional masking (negative suppression). The average amount of suppression was −1.0 dB. ANOVA tests shoed significantly more overshoot and less suppression in females than males, and significantly higher thresholds in left than right ears in the overshoot conditions. Results will be discussed in terms of possible individual, sex, and ear differences in efferent inhibition. [Work supported by NIH.]