Abstract
Cross-modal interactions can lead to enhancement of visual perception, even for visual events below awareness. However, the underlying mechanism is still unclear. Can purely bottom-up cross-modal integration break through the threshold of awareness? We used a binocular rivalry paradigm to measure perceptual switches after brief flashes or sounds which, sometimes, co-occurred. When flashes at the suppressed eye coincided with sounds, perceptual switches occurred the earliest. Yet, contrary to the hypothesis of cross-modal integration, this facilitation never surpassed the assumption of probability summation of independent sensory signals. A follow-up experiment replicated the same pattern of results using silent gaps embedded in continuous noise, instead of sounds. This manipulation should weaken putative sound-flash integration, although keep them salient as bottom-up attention cues. Additional results showed that spatial congruency between flashes and sounds did not determine the effectiveness of cross-modal facilitation, which was again not better than probability summation. Thus, the present findings fail to fully support the hypothesis of bottom-up cross-modal integration, above and beyond the independent contribution of two transient signals, as an account for cross-modal enhancement of visual events below level of awareness.
Highlights
Times between rival percepts[25,26] or change alternation rate[27] and, what is more, alternation can even stop altogether in the absence of top-down attention[28,29]
The focus of interest is on the conditions where the Gabor is suppressed, and the measure consists of changes in perceptual state following events presented on the suppressed Gabor patch, while participants report seeing the radial checkerboard (AVS: audiovisual suppressed, VS: visual suppressed, AS: audio is presented as Gabor patch is suppressed)
Dominant conditions were introduced to balance out stimuli, and refer to when events are presented on the currently seen Gabor patch (AVD: audiovisual dominant, VD: visual dominant, AD: Gabor patch was dominant at the moment of audio presentation) (Fig. 1A)
Summary
Times between rival percepts[25,26] or change alternation rate[27] and, what is more, alternation can even stop altogether in the absence of top-down attention[28,29]. We ran a Repeated Measures ANOVA (with Greenhouse-Geisser correction where appropriate) on the Mean Time to Switch (see Methods) latency data with the following, within participants’ factors: percept dominance (Gabor dominant, Gabor suppressed) and event modality (audio, visual, audiovisual).
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