When a subject in free field is presented with a test click and a simulated echo (originating from different positions on the horizontal plane), the degree of suppression of the echo increases with the number of clicks that precedes the test click [Freyman etal., J. Acoust. Soc. Am. 90, 874–884 (1991)]. Two experiments were conducted to investigate aspects of this buildup of echo suppression. Echo suppression for a test click was quantified by measuring echo threshold (i.e., the echo delay for which subjects could just identify the direction of the echo) in various conditions in which the test click was preceded by a click train. In experiment 1, echo threshold was largest (the maximum buildup occurred) when the echo delay in the preceding click train was 10–20 ms. Experiment 2 investigated the effect of the spatial positions of the preceding train and its echo. For subjects who showed echo suppression buildup, it was maximal in those cases when the train’s echo was in the same position as the test click’s echo. Results will be discussed in terms of the spatial and temporal characteristics underlying the buildup of echo suppression. [Work supported by NIH.]

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