Buildup and bistability in auditory streaming as an evidence accumulation process with saturation.

Quynh-Anh Nguyen,Rodica Curtu,John Rinzel,Wolfgang Einhäuser

doi:10.1371/journal.pcbi.1008152

Abstract

A repeating triplet-sequence ABA− of non-overlapping brief tones, A and B, is a valued paradigm for studying auditory stream formation and the cocktail party problem. The stimulus is “heard” either as a galloping pattern (integration) or as two interleaved streams (segregation); the initial percept is typically integration then followed by spontaneous alternations between segregation and integration, each being dominant for a few seconds. The probability of segregation grows over seconds, from near-zero to a steady value, defining the buildup function, BUF. Its stationary level increases with the difference in tone frequencies, DF, and the BUF rises faster. Percept durations have DF-dependent means and are gamma-like distributed. Behavioral and computational studies usually characterize triplet streaming either during alternations or during buildup. Here, our experimental design and modeling encompass both. We propose a pseudo-neuromechanistic model that incorporates spiking activity in primary auditory cortex, A1, as input and resolves perception along two network-layers downstream of A1. Our model is straightforward and intuitive. It describes the noisy accumulation of evidence against the current percept which generates switches when reaching a threshold. Accumulation can saturate either above or below threshold; if below, the switching dynamics resemble noise-induced transitions from an attractor state. Our model accounts quantitatively for three key features of data: the BUFs, mean durations, and normalized dominance duration distributions, at various DF values. It describes perceptual alternations without competition per se, and underscores that treating triplets in the sequence independently and averaging across trials, as implemented in earlier widely cited studies, is inadequate.

Highlights

Stimulus sequences of interleaved A and B pure tones have been widely used in studying segregation of distinct objects in an auditory scene, in human psychophysics [1,2,3,4,5,6], invasive neurophysiology [1, 3, 7, 8], or in experiments implementing both [9]
Our results underscore that assessing individual triplets independently and averaging across trials, as in some earlier studies, is inadequate
We propose that the model is not competition-based it shares some features of such approaches: Adaptation is key in competition dynamics; evidence accumulation might be viewed as recovery from adaptation

Summary

Introduction

Stimulus sequences of interleaved A and B pure tones have been widely used in studying segregation of distinct objects in an auditory scene (auditory streaming), in human psychophysics [1,2,3,4,5,6], invasive neurophysiology [1, 3, 7, 8], or in experiments implementing both [9]. The initial percept is typically integration but within seconds the probability of segregation increases (“the buildup phase”) and perceptual switching eventually occurs (“perceptual bistability”). Time courses of spiking activity (macaque, primary auditory cortex, A1, [1]) show dynamical features (adaptation over 1-2 seconds) that were interpreted as neural correlates of buildup, the behavioral and physiological experiments were not conducted together [1, 3]

Results

Discussion

Conclusion