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

3aPP4. The relative contribution of target IDTs and distractor IDLs in judgments of laterality.

R. H. Dye

Parmly Hear. Inst., Loyola Univ., 6525 N. Sheridan Rd., Chicago, IL 60626

M. A. Stellmack

Waisman Ctr., Univ. of Wisconsin, Madison, WI 53706

A stimulus-classification paradigm was used to examine the extent to which interaural differences of time (IDTs) and interaural differences of level (IDLs) interact across the frequency domain. The target was a 753-Hz tone presented with one of ten IDTs (-90 to +90 (mu)s). The distractor was 353, 553, 953, 1153, 1753, or 2753 Hz (fixed within a block of trials), presented with one of ten IDLs (-9 to +9 dB). Each test interval was preceded by a diotic presentation of the target alone. The duration of the signals was 200 ms. Each block of 100 trials presented each combination of target-distractor interaural differences once. Subjects indicated whether the target appeared to the left or right of the intracranial midline. The relative salience of the target IDT and the distractor IDL was assessed by the slope of the best linear boundary between left and right responses. For conditions in which the distractor was 200 Hz above or below the target, distractor and target information ``traded'' at about 1 dB/10 (mu)s. At wide frequency separations the slopes were steeper for most listeners, indicating greater ability to lateralize the time-delayed target independently of the distractor. [Work supported by NIH.]