Temporal Dynamics of Auditory and Visual Bistability Reveal Common Principles of Perceptual Organization

Abstract

When dealing with natural scenes, sensory systems have to process an often messy and ambiguous flow of information. A stable perceptual organization nevertheless has to be achieved in order to guide behavior. The neural mechanisms involved can be highlighted by intrinsically ambiguous situations. In such cases, bistable perception occurs: distinct interpretations of the unchanging stimulus alternate spontaneously in the mind of the observer. Bistable stimuli have been used extensively for more than two centuries to study visual perception. Here we demonstrate that bistable perception also occurs in the auditory modality. We compared the temporal dynamics of percept alternations observed during auditory streaming with those observed for visual plaids and the susceptibilities of both modalities to volitional control. Strong similarities indicate that auditory and visual alternations share common principles of perceptual bistability. The absence of correlation across modalities for subject-specific biases, however, suggests that these common principles are implemented at least partly independently across sensory modalities. We propose that visual and auditory perceptual organization could rely on distributed but functionally similar neural competition mechanisms aimed at resolving sensory ambiguities.

The initial phase of auditory and visual scene analysis

“…For tristable perception (first two groups of bars), durations differed significantly: F(2, 578) ¼ 104, p , 10 -15 , effect size (partial h 2 ) p h 2 ¼ 0.27 (290 trials included). The first coherent percept was longer than the subsequent coherent percepts (what we called the inertia of the first percept), as observed previously [16,27,29,30]. That was not the case for bistable perception due to occlusion: F(2, 572) ¼ 4.8, p ¼ 0.009, p h 2 ¼ 0.016 (287 trials included; the p-value is significant but the very small effect size indicates that the difference is in fact negligible; moreover, it is only due to a minor difference between the second and the third coherent percepts).…”

“…Interestingly, in all of the published data, after the initial build up, the probability of hearing two streams stabilizes below 100%. As pointed out by Pressnitzer & Hupé [16], this indicates that there are subsequent perceptual alternations back and forth to a one-stream percept after the initial build up. Perceptual reports for long-lasting sequences confirmed that streaming was indeed a bistable phenomenon [16][17][18].…”

Properties of auditory stream formation

“…If the frequency separation is less than a (smaller) critical value, called the fission boundary (FB [2]), a single stream is usually heard, even when the subject is instructed to try to hear two streams. However, even for very small or very large frequency separations, the percept may flip if the sequence is presented for a long time [3,17]. In other words, bistability occurs.…”

Minding time in an amodal representational space

“…For instance, a steady patch of light displayed extra-foveally eventually fades away from perception ( Troxler 1804); when presented with a steady ambiguous stimulus, perception oscillates between the possible perceptual interpretations whether in vision (e.g. the Necker cube) or in audition (Pressnitzer & Hupé 2006). Llinás et al (1998) remarked that external stimulations act as modulations of ongoing activity not as triggers of brain activity: activity at a given instant incorporates and is partially determined by the system state just prior to this instant.…”