Modelling the Emergence and Dynamics of Perceptual Organisation in Auditory Streaming

Abstract

Many sound sources can only be recognised from the pattern of sounds they emit, and not from the individual sound events that make up their emission sequences. Auditory scene analysis addresses the difficult task of interpreting the sound world in terms of an unknown number of discrete sound sources (causes) with possibly overlapping signals, and therefore of associating each event with the appropriate source. There are potentially many different ways in which incoming events can be assigned to different causes, which means that the auditory system has to choose between them. This problem has been studied for many years using the auditory streaming paradigm, and recently it has become apparent that instead of making one fixed perceptual decision, given sufficient time, auditory perception switches back and forth between the alternatives—a phenomenon known as perceptual bi- or multi-stability. We propose a new model of auditory scene analysis at the core of which is a process that seeks to discover predictable patterns in the ongoing sound sequence. Representations of predictable fragments are created on the fly, and are maintained, strengthened or weakened on the basis of their predictive success, and conflict with other representations. Auditory perceptual organisation emerges spontaneously from the nature of the competition between these representations. We present detailed comparisons between the model simulations and data from an auditory streaming experiment, and show that the model accounts for many important findings, including: the emergence of, and switching between, alternative organisations; the influence of stimulus parameters on perceptual dominance, switching rate and perceptual phase durations; and the build-up of auditory streaming. The principal contribution of the model is to show that a two-stage process of pattern discovery and competition between incompatible patterns can account for both the contents (perceptual organisations) and the dynamics of human perception in auditory streaming.

Feature Predictability Flexibly Supports Auditory Stream Segregation or Integration

“…the contrast of conditions 1 and 3). This result further supports the view that predictive relations between tones increase their sequential linkage and thus their perceptual coherence in an auditory stream ( [16][17][18]33]; see also early work by [6,19,21,22]). …”

“…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.…”

“…The independent manipulation of predictability was possible by systematically changing the sequential linkage between successive tones within each set ('A-A-A' and 'B-B-B') or across the sets ('A-B' and 'B-A'). Tones that are predictive of each other can be assumed to be more strongly linked in perception, and thus should be more likely to form a coherent stream [16][17][18]33]. This Manuscript submitted to Acta Acustica Bendixen et al 18 idea had been empirically demonstrated by introducing predictability separately into the 'A' and 'B' tone sets and showing that this increases stream segregation relative to an unpredictable control condition [5,30].…”

“…This was achieved by systematically changing the sequential dependencies between successive tones within and/or across the 'ABA-' triplets, such that these tones would or would not be predictive of each other. In the framework suggested by [18], this corresponds to strengthening or weakening the links between pairs of sounds, which would have immediate consequences on their perceptual coherence (see also [33]). …”

The effects of rhythm and melody on auditory stream segregation

“…Competitiveness and stability may be two independent attributes of proto-objects. Alternatively, it is possible that a common "activation" attribute (see Mill et al, 2013) is affected differently by certain cues depending on whether the proto-object is dominant or not. Bendixen and colleagues (2010) implicitly suggested the latter by assuming that the regularity of their temporal patterns is only detected when the corresponding protoobject is dominant.…”