SUDDEN CHANGES IN SPECTRUM OF AN ECHO CAUSE A BREAKDOWN OF THE PRECEDENCE EFFECT

The effect of changing the frequency components of an echo relative to the sound source was examined in a two-choice discrimination task. Su bjects sat in an anechoic chamber and discriminated the direction of t he lag noise burst within a lead-lag pair presented over loudspeakers. The leading noise burst was broadband, and the lagging burst was eith er high-or low-pass filtered. On some conditions, this test burst pair was preceded by a conditioning train of burst pairs, which also had a broadband lead and either a high-or low-frequency lag. When the frequ ency content of the echo was held constant across the conditioning tra in and test burst pair, echo suppression that was built up during the repeating train was maintained for the test burst pair, shown by the s ubjects' poor performance in detecting the location of the lagging bur st. By comparison, subjects had little difficulty in localizing the la gging burst when the frequency content of the echo changed between the conditioning train and the test burst, indicating that any buildup of suppression during the train was broken when the lagging burst's spec trum shifted. The data are consistent with an interpretation in which echo suppression is temporarily broken when listeners' built-up expect ations about room acoustics are violated.