Abstract
Stream segregation for a test sequence comprising high-frequency (H) and low-frequency (L) pure tones, presented in a galloping rhythm, is much greater when preceded by a constant-frequency induction sequence matching one subset than by an inducer configured like the test sequence; this difference persists for several seconds. It has been proposed that constant-frequency inducers promote stream segregation by capturing the matching subset of test-sequence tones into an on-going, pre-established stream. This explanation was evaluated using 2-s induction sequences followed by longer test sequences (12-20 s). Listeners reported the number of streams heard throughout the test sequence. Experiment 1 used LHL- sequences and one or other subset of inducer tones was attenuated (0-24 dB in 6-dB steps, and ∞). Greater attenuation usually caused a progressive increase in segregation, towards that following the constant-frequency inducer. Experiment 2 used HLH- sequences and the L inducer tones were raised or lowered in frequency relative to their test-sequence counterparts (ΔfI = 0, 0.5, 1.0, or 1.5 × ΔfT ). Either change greatly increased segregation. These results are concordant with the notion of attention switching to new sounds but contradict the stream-capture hypothesis, unless a "proto-object" corresponding to the continuing subset is assumed to form during the induction sequence.
Highlights
Auditory stream segregation refers to the phenomenon in which a sequence of sounds is perceived as comprising more than one auditory stream, each corresponding to a distinct acoustic source in the environment (Bregman and Campbell, 1971)
The analysis of variance (ANOVA) showed significant main effects of frequency separation, induction condition, and time interval (p 0.001 in all cases). These outcomes indicate that (1) larger frequency separations increased the extent of reported segregation, even after the period of most substantial change in the tendency to hear two streams was over; (2) smaller, effects of induction condition on stream segregation persisted into the latter half of the sequence—in particular, mean stream segregation remained greatest following the L-tones-only induction sequence (C6); (3) more slowly, reported stream segregation continued on average to rise in the latter portion of the test sequence
The experiments reported here have shown, to our knowledge for the first time, that induction sequences for which one subset of tones precisely matches its counterpart in the test sequence, but the other does not, have the opposite effect—they cause more segregated percepts
Summary
Auditory stream segregation refers to the phenomenon in which a sequence of sounds is perceived as comprising more than one auditory stream, each corresponding to a distinct acoustic source in the environment (Bregman and Campbell, 1971). The effect of a given induction sequence on the perception of the subsequent test sequence can be assessed by comparing it with two control cases—one in which the properties of the induction sequence match exactly those of the test sequence and one in which the induction sequence is replaced by silence or continuous wideband noise Studies using this or related approaches have shown that there is typically a nearimmediate loss of build-up, referred to as resetting, following a sudden change of sufficient magnitude in the acoustic properties of the AF sequence—e.g., a change in ear of presentation, center frequency, or lateralization (e.g., Anstis and Saida, 1985; Rogers and Bregman, 1998). We consider attention switching to new sounds as a possible alternative or additional explanation for the results obtained
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