Perceptual bistability in auditory streaming: How much do stimulus features matter?

Abstract

The auditory two-tone streaming paradigm has been used extensively to study the mechanisms that underlie the decomposition of the auditory input into coherent sound sequences. Using longer tone sequences than usual in the literature, we show that listeners hold their first percept of the sound sequence for a relatively long period, after which perception switches between two or more alternative sound organizations, each held on average for a much shorter duration. The first percept also differs from subsequent ones in that stimulus parameters influence its quality and duration to a far greater degree than the subsequent ones. We propose an account of auditory streaming in terms of rivalry between competing temporal associations based on two sets of processes. The formation of associations (discovery of alternative interpretations) mainly affects the first percept by determining which sound group is discovered first and how long it takes for alternative groups to be established. In contrast, subsequent percepts arise from stochastic switching between the alternatives, the dynamics of which are determined by competitive interactions between the set of coexisting interpretations.

Feature Predictability Flexibly Supports Auditory Stream Segregation or Integration

“…This suggests that all organizations are "equal" in that they must be supported by cues present in the auditory input. This conclusion is consistent with other recent work challenging the view of "integration by default" [9,46].…”

“…'Both' denotes a perceptual category including patterns be other perceptual alternatives beyond the classical integrated and segregated patterns described by [7]; hence listeners were usually not given the opportunity to denote the 'Both' percept by a corresponding response button. Consequently, not much is known about the conditions under which the 'Both' percept occurs, other than that it appears more rarely than the integrated and segregated alternatives, and usually enters perceptual competition later than those [9,40]. The present finding that the 'Both' percept becomes more frequent when neither the integrated nor the segregated perceptual organizations are predictable can be interpreted in the framework of perceptual coherence [16][17][18]33]: When the two predominant alternatives (integrated and segregated) do not provide "satisfactory" explanations of the sound input due to the absence of predictability, perception may start exploring other grouping alternatives.…”

“…Depending on the amount of feature difference and the rate of tone presentation, participants tend to perceive the 'ABA-' sequence as originating from one sound source (integrated) with a galloping rhythm, or from two different sound sources (segregated), one made up of the 'A' tones, and the other made up of the 'B' tones repeating at half the rate of the 'A' tones [3,7]. With prolonged exposure to such sequences, perception switches back and forth between the integrated and segregated (and possibly Manuscript submitted to Acta Acustica Bendixen et al 5 other) alternatives [8][9][10][11][12][13][14][15]. This perceptual bi-or multistability has been interpreted as a sign of the system exploring different grouping alternatives [16][17][18].…”

The role of perceived source location in auditory stream segregation: Separation affects sound organization, common fate does not

“…The assignment of the keys was counterbalanced across participants. The 'integrated' and 'segregated' percepts were explained and illustrated (both with sound examples and visual illustrations) to the participants before the experiment, and the experimenter made sure they understood the task (for further details about the instructions, see Denham et al, 2013). Because there is no single prototype for the "both" percept, listeners were not trained specifically on it, but were only told to use it when they experienced both an integrated and a segregated pattern, in parallel.…”

“…The state of the two response keys was sampled at a 250 Hz rate, and the data was analyzed similarly to the procedure used in Denham et al (2013). For each perceptual phase (i.e., the time interval between two consecutive perceptual switches), the logarithm of its duration in milliseconds and the reported percept was extracted.…”