DETECTING SIGNALS OF UNEXPECTED OR UNCERTAIN DURATIONS

Expectation of signal duration influences the signal detectability. Th is is demonstrated in two experiments in which percent correct was mea sured for both tonal and noise signals whose durations were either une xpected or uncertain. In both experiments, the signal at each duration was set to have a d' of about 1.5 when that duration was presented al one and expected. When the six subjects were led to expect a short- or a long-duration signal using the probe-signal method, the detectabili ty of signals decreased to near chance as the signal duration deviated from the expected value (experiment 1). When the subjects were led to expect a range of durations, the detectability was only slightly wors e than when each signal was presented alone (experiment 2). Those resu lts suggest that listeners adjust their temporal-integration intervals according to the demand of the specific task. Finally, the results ob tained with the noise signal were analyzed using the multiple-look mod el and a modified energy-detector model. Assuming that the integration interval is matched to the expected signal duration, both models pred ict the detection of signals having unexpected durations reasonably we ll. Both models, however, fail to predict the small effect of duration uncertainty. (C) 1995 Acoustical Society of America.