Two-channel detection of the missing event

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Continuing the investigation of two-channel processing mechanisms, this study explored the effect of defining a signal event as a gap in a continuous sinusoid. The two channels were differentiated spatially by earphone channel; temporally by use of contiguous, non-overlapping observation intervals; and spectrally by use of differential, channel signal frequencies. The observer's task was to make two channel-specific, yes-no decisions concerning the presence of signal events. Signal events in each channel were independently determined and occurred with a probability of 0.5. Three two-channel conditions were explored: a pulse condition where signal events were 100-msec sinusoids, a gap condition where signal events were 100-msec gaps in otherwise continuous sinusoids, and a mixed condition where signal events were defined as a gap in one channel but as a pulse in the other. Two-channel performance in each condition was evaluated relative to signal-channel performance (a task where signal events could only occur in one channel). In the gap detection conditions, approximately a 4-dB increase in level was required to equate performance with that of pulse detection conditions. With respect to signal-channel performance, two-channel decrements were greatest in the gap condition, less in the mixed condition, and least in the pulse condition. Two-channel performance in the pulse condition was similar to that obtained in equivalent conditions in earlier studies. Performance was much better in the pulse and gap conditions in the absence of a contralateral signal event. This effect was minimal or absent in the mixed condition.