Coherence detection: effects of frequency, frequency uncertainty, and onset/offset delays.

The detectability of a sequence of equal-frequency (coherent) tonal components embedded in random, multiburst maskers was evaluated. The masker was comprised of tonal components located in a time-by-frequency spectrogram with eight 30 ms time columns and 29 frequency rows ranging logarithmically from 200 to 5000 Hz. The probability that a tone occurred in any one cell of the spectrogram, p, was the independent variable. The signal and masker components were of equal duration and equal level. Using a yes/no procedure, threshold values of p were estimated for five signal frequencies (220, 445, 1000, 2245, 4490 Hz) and when the signal frequency was random. Thresholds were worst for the random-frequency signal and best for the fixed 1000 Hz signal. In additional conditions, the value of p was fixed and the signal components were delayed relative to the masker components. A 1 ms delay provided better sensitivity (d' grew from 0.5 to 1) for all but the lowest signal frequency tested. An analysis of no-signal trials revealed that false alarm rates were higher when components falling at the signal frequency were consecutive than when they were distributed across bursts. Thus, coherence rather than total energy at the signal frequency is important for signal detection.