Buildup and breakdown of the precedence effect

Abstract

Dynamic variations in the strength of echo suppression were investigated through earphone simulation of the free-field precedence effect. Each test stimulus consisted of two click pairs, with the interaural time parameters of the leading and lagging pairs reflecting stimuli originating from opposite sides of the head. Echo thresholds, the minimum lagging click delay required for subjects to report hearing an echo click, were obtained in two basic conditions: (a) test click presented in isolation, and (b) test click preceded by a train of clicks identical to the test click. The most striking finding was that the presence of the preceding click train usually elevated the echo threshold of the test stimulus relative to its threshold when presented in isolation, suggesting that echo suppression builds up during the click train. The magnitude of the effect was influenced by the number of clicks in the train and the period of silence between the end of the train and the test click. The effect is surprisingly persistent, lasting through several seconds of silence. Partial release from the built-up suppression occurred when the lead and lag locations of the test click were reversed from the clicks in the preceding train. [Work supported by NSF.]