EXTENTS OF LATERALITY AND BINAURAL INTERFERENCE EFFECTS

Extents of laterality produced by ongoing interaural time delays (ITDs ) within high-frequency sinusoidally amplitude-modulated (SAM) target tones were measured in the presence or absence of a second, spectrally remote, diotic, SAM tone. The spectrally remote SAM tones had recentl y been shown to reduce sensitivity to ITDs conveyed by a 4-kHz SAM ton e in a previous experiment employing the same listeners [L. M. Heller and C. Trahiotis, J. Acoust. Soc. Am. 97 1808-1816 (1995)]. All SAM to nes were 100% modulated at 250 Hz and were presented at 77 dB SPL for a duration of 250 ms. The SAM target tone was centered at 4 kHz and th e lower-frequency SAM tones were centered at either 500 Hz, 1 kHz, or 2 kHz. The data indicate that spectrally remote, diotic, SAM tones ''p ull'' the lateral position of a 4-kHz SAM tone toward the midline, eve n when the 4-kHz SAM tone contains an ITD of up to 400 or 600 mu S. Th is means that effects of spectrally remote information are not confine d to tasks which require that listeners detect, or discriminated betwe en, threshold amounts of ITD. Analyses revealed that changes in latera l position, as measured by an acoustic pointing task, cannot in and of themselves account for the interference effects found in discriminati on tasks with similar stimuli. It was found however, that Buell and Ha fter's [J. Acoust. Soc. Am. 90, 1894-1900 (1991)] weighted-combination model, when augmented to include measures of laterality as well as me asures of discriminability, could provide reasonably accurate predicti ons of the amounts of interference obtained in the discrimination task . (C) 1996 Acoustical Society of America.