Charles S. Watson
Xiaofeng Li
Dept. of Speech and Hear. Sci., Indiana Univ., Bloomington, IN 47405
In a modification of the previous profile discrimination experiments [summarized in D. M. Green, Profile Analysis (Oxford U.P., New York, 1988)], intensity increments were introduced at one of ten temporal positions during the overall duration of 11-tone profiles. When both the frequency and the temporal position of intensity increments are varied randomly from trial to trial, listeners show considerably lower thresholds for increments occuring at higher frequencies, and later in time. These results are, in some cases, quite similar to the distribution of selective attention to individual tonal components of multi-tone patterns [e.g., Watson et al., J. Acoust. Soc. Am. 60, 1176 (1976)]. When the same increments are presented under minimal-uncertainty conditions (i.e., at a single frequency and temporal position within each block of adaptive-tracking trials), thresholds are reduced by as much as 6--8 dB. These results suggest a common source of the distribution of selective attention to the components of sequences of individual tones, and to the spectral-temporal range of the spectrally richer and more representative profile stimuli. [Work supported by NIH and AFOSR.]