Abstract
In binocular rivalry (BR), sensory input remains the same yet subjective experience fluctuates irremediably between two mutually exclusive representations. We investigated the perceptual stabilization effect of an additional sound on the BR dynamics using speech stimuli known to involve robust audiovisual (AV) interactions at several cortical levels. Subjects sensitive to the McGurk effect were presented looping videos of rivaling faces uttering /aba/ and /aga/, respectively, while synchronously hearing the voice /aba/. They reported continuously the dominant percept, either observing passively or trying actively to promote one of the faces. The few studies that investigated the influence of information from an external modality on perceptual competition reported results that seem at first sight inconsistent. Since these differences could stem from how well the modalities matched, we addressed this by comparing two levels of AV congruence: real (/aba/ viseme) vs. illusory (/aga/ viseme producing the /ada/ McGurk fusion). First, adding the voice /aba/ stabilized both real and illusory congruent lips percept. Second, real congruence of the added voice improved volitional control whereas illusory congruence did not, suggesting a graded contribution to the top-down sensitivity control of selective attention. In conclusion, a congruent sound enhanced considerably attentional control over the perceptual outcome selection; however, differences between passive stabilization and active control according to AV congruency suggest these are governed by two distinct mechanisms. Based on existing theoretical models of BR, selective attention and AV interaction in speech perception, we provide a general interpretation of our findings.
Highlights
In everyday life, phenomenal experience builds upon evidence about the outside world provided by our senses combined with internal expectations
Recent findings suggest that the same brain area, the intraparietal sulcus (IPS) known to host spatial maps and saliency filters involved in attentional control, would be at the core of the perceptual selection process in Binocular rivalry (BR) (Zaretskaya et al, 2010)
We measured the effect of an additional voice on the competition dynamics of talking lips manipulating the type of AV congruence for participants highly sensitive to the McGurk effect (41.4% of our initial set)
Summary
Phenomenal experience builds upon evidence about the outside world provided by our senses combined with internal expectations. Selective attention can bias perceptual alternations in order to promote one of the rivaling percepts by maintaining it dominant as long as possible (Chong et al, 2005) and switch back to it when suppressed (Kanai et al, 2006). In this project, we used rivaling natural videos of moving lips to assess how a relevant voice sound interferes with the selection of the visual outcome
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