CORRELATED INDIVIDUAL-DIFFERENCES IN CONDITIONS USED TO MEASURE PSYCHOPHYSICAL SUPPRESSION AND SIGNAL ENHANCEMENT

Two-tone suppression and notched-noise signal enhancement (overshoot) were measured at 1000 Hz using standard procedures in 40 normal-hearin g, naive adults, counterbalanced for sex, listening ear, and testing o rder. The threshold range across subjects for the same condition often exceeded 30 dB. In the suppression conditions, for some subjects the 20-ms forward-masked signal was as much as 15 dB easier to detect when the tonal masker (1000 Hz) and tonal suppressor (1150 Hz) were presen ted together, than when the masker was presented alone, indicating sup pression. For other subjects, however, presenting the masker and suppr essor together increased thresholds by as much as 13 dB, indicating ad ditional masking. On average, adding the suppressor to the masker incr eased threshold by 0.6 dB. In the enhancement conditions, for every su bject the 20-ms signal was harder to detect when it was presented at t he onset of a 500-ms notched-noise masker (notch width: 1000 Hz) than when signal onset was delayed by 400 ms, and was hardest to detect whe n the signal and masker were gated on and off together for 20 ms. The average thresholds were 7 and 19 dB higher for the two conditions in w hich the signal was presented at masker onset than for the condition i n which the signal was presented after a delay, indicating signal enha ncement. The thresholds in all of the listening conditions appeared to be primarily determined by a single factor. However, it is not clear whether the best designation for this factor would be sharpness of fre quency tuning or across-channel inhibitory strength. (C) 1996 Acoustic al Society of America.