GAP DETECTION AND THE PRECEDENCE EFFECT IN YOUNG AND OLD ADULTS

Thresholds for detecting a gap between two Gaussian-enveloped (standar d deviation=0.5 ms), 2-kHz tones were determined in young and old list eners. The gap-detection thresholds of old adults were more variable a nd about twice as large as those obtained from young adults. Moreover, gap-detection thresholds were not correlated with audiometric thresho lds in either group. Estimates of the width of the temporal window of young subjects, based on the detection of a gap between two tone pips, were smaller than those typically obtained when a relatively long dur ation pure tone is interrupted [Moore et al., J. Acoust. Sec. Am. 85, 1266-1275 (1989)]. Because the amount of time it takes to recover from an adapting stimulus is likely to affect gap detection thresholds [Gl asberg et al., J. Acoust. Sec. Am. 81, 1546-1556 (1987)], smaller esti mates of temporal window size would be expected in this paradigm if th e amount of adaptation produced by the first tone pip was negligible. The larger gap-detection thresholds of old subjects indicate that they may have larger temporal windows than young subjects. The lack of cor relation between audiometric and gap-detection thresholds indicates th at this loss of temporal acuity is not related to the degree of sensor ineural hearing loss. In a second experiment on the precedence effect using the same subjects, a Gaussian-enveloped tone was presented over earphones to the left ear followed by the same tone pip presented to t he right ear. To more realistically approximate a sound field situatio n, the tone pip presented to each ear was followed 0.6 ms later by an attenuated version presented to the contralateral ear. The delay betwe en the left- and right-ear tone-pips was varied and the transition poi nt between hearing a single tone on the left, and hearing two such sou nds in close succession (one coming from the left and the other from t he right) was determined. The transition point in this experiment did not differ between young and old subjects nor were these transition po ints correlated with gap-detection thresholds. These results indicate that monaural temporal acuity and binaural echo suppression may be bas ed on different processes.