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Crossmodal associations modulate multisensory spatial integration Jonathan Tong 1,2 & Lux Li 1

&

Patrick Bruns 1 & Brigitte Röder 1

# The Author(s) 2020

Abstract According to the Bayesian framework of multisensory integration, audiovisual stimuli associated with a stronger prior belief that they share a common cause (i.e., causal prior) are predicted to result in a greater degree of perceptual binding and therefore greater audiovisual integration. In the present psychophysical study, we systematically manipulated the causal prior while keeping sensory evidence constant. We paired auditory and visual stimuli during an association phase to be spatiotemporally either congruent or incongruent, with the goal of driving the causal prior in opposite directions for different audiovisual pairs. Following this association phase, every pairwise combination of the auditory and visual stimuli was tested in a typical ventriloquism-effect (VE) paradigm. The size of the VE (i.e., the shift of auditory localization towards the spatially discrepant visual stimulus) indicated the degree of multisensory integration. Results showed that exposure to an audiovisual pairing as spatiotemporally congruent compared to incongruent resulted in a larger subsequent VE (Experiment 1). This effect was further confirmed in a second VE paradigm, where the congruent and the incongruent visual stimuli flanked the auditory stimulus, and a VE in the direction of the congruent visual stimulus was shown (Experiment 2). Since the unisensory reliabilities for the auditory or visual components did not change after the association phase, the observed effects are likely due to changes in multisensory binding by association learning. As suggested by Bayesian theories of multisensory processing, our findings support the existence of crossmodal causal priors that are flexibly shaped by experience in a changing world. Keywords Multisensory processing . Audiovisual integration . Ventriloquism effect . Causal inference . Multisensory binding . Crossmodal association . Priors . Causal prior . Coupling prior . Bayesian

Jonathan Tong and Lux Li are joint first authors. Public significance statement When processing information from multiple senses, an observer must decide which inputs are caused by the same events and therefore should be integrated. The present study investigated how prior experience with auditory and visual stimuli as either co-occurring or never co-occurring in space and time mediates the degree of audiovisual integration. We found that stimuli that were learned to co-occur were later more strongly integrated, that is, localized closer to each other. These results demonstrate that, rather than relying on the sensory input only, we use prior knowledge that we continuously update in a changing world when we integrate input across sensory modalities. Electronic supplementary material The online version of this article (https://doi.org/10.3758/s13414-020-02083-2) contains supplementary material, which is available to authorized users. * Lux Li luxi.l