Forty listeners were tested on two tasks known to show large individual differences in performance. In one task, termed sample discrimination, pairs of target tones were drawn from each of two overlapping frequency distributions, and listeners indicated which pair came from the higher distribution. Target tones were presented alone and in the presence of two flanking context tones that were either fixed at 500 and 4000 Hz or had Gaussian variation centered at these two frequencies. In the second task, masked thresholds were determined for a 1000-Hz tone in the presence of ten-component, random-frequency, simultaneous maskers. The maskers were drawn on each presentation from a pool of either 200 or 10 waveforms. For sample discrimination, the range of performance was large for both the no-context and fixed-frequency context conditions. For the Gaussian-context condition, few listeners exceeded chance performance. Significant effects of testing order were found, with exposure to Gaussian-context conditions degrading later performance. For masking, performance did not differ for large versus small waveform pools, and the 35-dB range of performance corroborated previous work. For both tasks, random-frequency context degraded performance for the majority of listeners. [Work supported by NIDCD.]
The effect of a temporal gap on detecting a 1000-Hz tone in the presence of 60-dB SPL simultaneous maskers was examined. Ten-component, random-frequency maskers and broadband-noise maskers were used in a 2-AFC adaptive task. Random-frequency components were drawn from 300 to 3000 Hz, excluding a 160-Hz band around the signal. Temporal gaps of 10, 20, 40, 80, and 160 ms were tested, positioned either at the onset, center, or offset of either the signal or the masker. Without gaps, both signal and masker durations were 200 ms. To maintain equal energy across all conditions, level compensation was applied when gaps were employed. For temporal gaps in either the multicomponent or noise masker, masked thresholds consistently decreased as gap duration increased. Gaps in the masker appeared to provide a temporal window for detection of the signal. However, for gaps in the signal, masked thresholds decreased with the multicomponent masker, but remained constant with broadband noise masker. With multicomponent maskers, the gaps appeared to reduce informational masking by perceptually segregating the signal from the masker. With broadband noise maskers, there was little informational masking and therefore the temporal gaps did not improve performance. [Work supported by NIDCD.]
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