Ensemble modeling of auditory streaming reveals potential sources of bistability across the perceptual hierarchy
Authors: Little David F. , Snyder Joel S. , Elhilali Mounya 
Published: April 2019

Perceptual bistability—the spontaneous fluctuation of perception between two interpretations of a stimulus—occurs when observing a large variety of ambiguous stimulus configurations. This phenomenon has the potential to serve as a tool for, among other things, understanding how function varies across individuals due to the large individual differences that manifest during perceptual bistability. Yet it remains difficult to interpret the functional processes at work, without knowing where bistability arises during perception. In this study we explore the hypothesis that bistability originates from multiple sources distributed across the perceptual hierarchy. We develop a hierarchical model of auditory processing comprised of three distinct levels: a Peripheral, tonotopic analysis, a Central analysis computing features found more centrally in the auditory system, and an Object analysis, where sounds are segmented into different streams. We model bistable perception within this system by injecting adaptation, inhibition and noise into one or all of the three levels of the hierarchy. We evaluate a large ensemble of variations of this hierarchical model, where each model has a different configuration of adaptation, inhibition and noise. This approach avoids the assumption that a single configuration must be invoked to explain the data. Each model is evaluated based on its ability to replicate two hallmarks of bistability during auditory streaming: the selectivity of bistability to specific stimulus configurations, and the characteristic log-normal pattern of perceptual switches. Consistent with a distributed origin, a broad range of model parameters across this hierarchy lead to a plausible form of perceptual bistability. The ensemble also appears to predict that greater individual variation in adaptation and inhibition occurs in later stages of perceptual processing.

Author summary

Our ability to experience the everyday world through our senses requires that we resolve numerous ambiguities present in the physical evidence available. This is accomplished, in part, through a series of hierarchical computations, in which stimulus interpretations grow increasingly abstract. Our ability to resolve ambiguity does not always succeed, such as during optical illusions. In this study, we examine a form of perceptual ambiguity called bistability—cases in which a single individual’s perception spontaneously switches back and forth between two interpretations of a single stimulus. A challenge in understanding bistability is that we don’t know where along the perceptual hierarchy it is generated. Here we test the idea that there are multiple origins by building a simulation of the auditory system. Consistent with a multi-source account of bistability, this simulation accurately predicts perception of a simple auditory stimulus when bistability originates from a number of different sources within the model. The data also indicate that individual differences during ambiguous perception may primarily originate from higher levels of the perceptual hierarchy. This result provides a clue for future work aiming to determine how auditory function differs across individual brains.