ASA 127th Meeting M.I.T. 1994 June 6-10

3aPP18. Sudden changes in simulated room acoustics influence echo suppression.

Richard L. Freyman

Dept. of Commun. Disord., Univ. of Massachusetts, Amherst, MA 01003

Rachel K. Clifton

Daniel D. McCall

Univ. of Massachusetts, Amherst, MA 01003

Listeners seated in an anechoic chamber discriminated the direction of the lag noise burst within a lead-lag pair. The lead loudspeakers were 42(degrees) or 48(degrees) left of midline, and the lag loudspeakers were 35(degrees) or 55(degrees) right. A train of noise bursts, during which the lag was always 45(degrees) right, preceded the test noise in some conditions. In the first experiment the lead was broadband (``B'') and lag was either high-(``H'') or low-pass (``L'') filtered. Discrimination of the test noise location was poorer when the B-L (lead-lag) test was preceded by a B-L train than when the test noise was presented in isolation, suggesting that echo suppression built up during the repetitious train. By comparison, discrimination of the B-L test was unaffected by a B-H train, indicating that any buildup of suppression during the train was broken when the lag's frequency shifted from H to L, which simulated a change in absorption of echoes by room surfaces. A second experiment in which the intensity of the lag varied between train and test produced similar results. The data are consistent with an interpretation in which echo suppression is temporarily broken when listeners' built-up expectations about room acoustics are violated. [Work supported by NIH DC01625.]