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

3pPP3. Binaural interference and grouping.

Trevor M. Shackleton

Exp. Psychol., Univ. of Sussex, Brighton BN1 9QG, UK

The threshold interaural time difference (ITD) of a target tone increases in the presence of spectrally remote distractor tones [e.g., R. H. Dye, J. Acoust. Soc. Am. 88, 2159--2170 (1990)]. It has been suggested that this is because ITD information is grouped across both target and distractor components [e.g., T. N. Buell and E. R. Hafter, J. Acoust. Soc. Am. 90, 1894--1900 (1991)]. If this is so, then the lateralization of the target should be shifted towards the lateralization of the distractor. Alternatively, the presence of a distractor could introduce extra discrimination noise, causing threshold ITDs to rise, but without affecting the target lateralization. Subjects reported whether a target tone presented with a variety of ITDs was perceived to the left or right of midline when a distractor tone was either not present, presented diotically, or presented with a supra-threshold ITD. The slope of the function relating the percentage of leftward responses to the ITD of the target decreased when a distractor was present (indicating a higher threshold). The functions were also shifted horizontally towards the ITD of the distractor. These results suggest that binaural interference results from grouping target and distractor components together. [Work supported by The Wellcome Trust.]