Abstract
The results of several experiments suggest that when an observer is asked to detect a burst of a sinusoid, he will often listen for signal level at frequencies far removed from that of the signal. For example, in one experiment, observers were asked to detect a 10-msec sinusoid, masked by wide-band noise and a continuous sinusoid 300 Hz lower in frequency than that of the signal. In one condition, the signal was high-pass filtered, and in another condition no filter was used. The filter was such that it reduced the total level of the signal by 23 dB. At low noise levels, despite the 23-dB signal-level reduction, detectability was only 8 dB poorer in the filtered condition. This result suggests that observers were detecting the signal by listening for off-frequency energy, probably high-frequency energy. In a second experiment observers detected a 10-msec sinusoid masked by an off-frequency continuous tone and by a 10-msec gated tone at the same frequency as the continuous tone. The gated masker was added either in phase or in quadrature with the continuous masker. Masking functions relating threshold signal level and gated masker level were identical for the in-phase and quadrature conditons. This result suggests that the effective masker in these conditions is the energy off the frequency of the masker. This energy, which is produced by the gated masker, is nearly the same for the in-phase and quadrature conditions. [Research supported by the National Institutes of Health, U. S. Public Health Service, Department of Health, Education, and Welfare.]
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