Perceptual Organization by Stephen Handel

Author:Stephen Handel
Language: eng
Format: epub, pdf
ISBN: 9783319963372
Publisher: Springer International Publishing

3.3 Auditory Multistability

One common approach to study auditory multistability is to make use of the stream segregation paradigm. In the simplest case, two sounds of different frequencies are recycled. If the frequencies are similar or the time interval between the offset of one and the onset of the next is long, the percept is of one oscillating pattern. As the frequency difference is increased, and/or the time interval is shortened, the continuous pattern breaks up and is perceived as two independent sequences or streams; one stream of the low-pitch tones, one stream of the high-pitch tones (Examples are found in Sound File 2.9). For these sequences, sound similarity dominates. In between, there are frequency and time intervals in which the percept switches between the two. In general, the initial percept is that of a single integrated cycling of the tones, another instance of the preference to perceive one source or object. The two interleaved streams percept appears later, as an alternative. After the initial swap, further swaps between the one- and two-stream percept occur after random time intervals. Clearly, the multistability of streaming and apparent visual movement (i.e., movement between the dots versus independent flashing dots, Fig. 3.3A) is analogous both in stimulus configuration and outcome.

The streaming paradigm can be expanded to include three frequencies (Thossen & Bendixen, 2017). The three tones 400 Hz, 635 Hz, and 1008 Hz cycle at the rate of five tones/sec. There are many possible ways of organizing the three tones. For example, the 400 Hz tone could form one stream and the 635 Hz + 1008 Hz tones could form the second. Moreover, the single-tone stream could be heard in the forefront or the two-tone stream could be heard in the forefront. In general, the streams were based on frequency, the 400 Hz tone versus the two higher pitches or the 1008 Hz tone against the two lower pitches. What is most relevant here is that the organization is multistable, and the average time between reversals was roughly 16 sec. The number and pattern of reversals differed greatly among the listeners, which make sense given the number of alternative organizations.

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