ASA 125th Meeting Ottawa 1993 May

3pPP3. Effects of different samples of reproducible noise on detection of a 20-Hz-wide interaural phase shift centered on 500 Hz.

A. N. Grange

W. A. Yost

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

Subjects' thresholds were first determined for detection of an interaural phase shift of a 20-Hz band of equal-amplitude wideband noise. The narrow-band target was centered on 500 Hz, and generated a dichotic, Huggins-type pitch. A diotic band of either 100, 125, 150, or 900 Hz symmetrically surrounded the target band. Interaural phases for frequency components outside of the diotic band were drawn randomly from a rectangular distribution. After thresholds were determined via a tracking procedure, 20 independent samples were generated for each condition at each subject's threshold. A two-interval forced choice task was used in which each interval was comprised of a 250-ms forward fringe followed by a 250-ms observation period. Sixty trials were presented in a block with each sample presented three times. Order of presentation was randomized across runs and each sample was presented a total of 96 times. P(C) ranged from chance (50%) to over 90% across samples having identical interaural parameters. In conditions where subjects' thresholds were similar, allowing the same set of samples to be used for two or more subjects, there was a strong inter-subject correspondence with respect to P(C). Possible sources of these sample-specific effects will be discussed. [Work supported by NIH.]