In a previous study on the ventriloquism aftereffect, we showed that medial parietal regions integrate audiovisual information within a trial and mediate the trial-by-trial aftereffect ( Park and Kayser, 2019), implying a role of parietal regions involved in spatial working memory and multisensory causal inference in trial-wise recalibration. Still, this hypothesis has not been directly tested. The trial-wise and cumulative biases differ in their specificity to the sensory features of the inducing stimuli and were suggested to arise from distinct neurophysiological correlates ( Bruns and Röder, 2015, 2019). This aftereffect increases with cumulative exposure to a consistent discrepancy, but seems to independently emerge trial by trial and following prolonged exposure ( Frissen et al., 2012 Bruns and Röder, 2015 Van der Burg et al., 2015 Watson et al., 2019 Kramer et al., 2020). During the ventriloquism aftereffect ( Canon, 1970 Radeau and Bertelson, 1974 Recanzone, 1998 Wozny and Shams, 2011 Bruns and Röder, 2015), the exposure to displaced acoustic and visual stimuli in an audiovisual trial reliably biases the perceived location of subsequent sounds received during a unisensory trial ( Woods and Recanzone, 2004 Frissen et al., 2012 Mendonça et al., 2015 Watson et al., 2019). Our environment changes on multiple timescales, and, not surprisingly, perceptual recalibration also emerges on distinct scales ( Bruns and Röder, 2015, 2019 Van der Burg et al., 2015 Bosen et al., 2017, 2018 Rohlf et al., 2020). Despite the importance of such adaptive multisensory processes in everyday life, their neural underpinnings remain unclear. Sensory recalibration serves to continuously adapt perception to discrepancies in our environment, such as the apparent displacement of the sight and sound of an object ( De Gelder and Bertelson, 2003 Chen and Vroomen, 2013). Our data suggest that parietal regions involved in multisensory and spatial memory mediate the aftereffect following both trial-wise and cumulative adaptation, but also show that additional and distinct processes are involved in consolidating and implementing the aftereffect following prolonged exposure. We here rephrase this hypothesis using human electroencephalography recordings. While this aftereffect emerges following trial-wise or cumulative exposure to multisensory discrepancies, it remained unclear whether both arise from a common neural substrate. These adaptive mechanisms exert a persistent influence on the perception of subsequent unisensory stimuli, known as the ventriloquism aftereffect. SIGNIFICANCE STATEMENT Our brain easily reconciles conflicting multisensory information, such as seeing an actress on screen while hearing her voice over headphones. Our results posit a central role of parietal regions in shaping multisensory spatial recalibration, suggest that frontal regions consolidate the behavioral bias for persistent multisensory discrepancies, but also show that the trial-wise and cumulative exposure bias sound position encoding via distinct neurophysiological processes. During the subsequent unisensory trial, both trial-wise and cumulative exposure bias the encoding of the acoustic information, but do so distinctly. Our results support the hypothesis that discrepant multisensory evidence shapes aftereffects on distinct timescales via common neurophysiological processes reflecting sensory inference and memory in parietal-occipital regions, while the cumulative exposure to consistent discrepancies additionally recruits prefrontal processes. We address this question by probing electroencephalography recordings from healthy humans (both sexes) for processes predictive of the aftereffect biases following the exposure to spatially offset audiovisual stimuli. Despite the importance of such adaptive mechanisms for interacting with environments that change over multiple timescales, it remains debated whether the ventriloquism aftereffects observed following trial-wise and cumulative exposure arise from the same neurophysiological substrate. A classic example is the ventriloquism aftereffect, which emerges following both cumulative (long-term) and trial-wise exposure to spatially discrepant multisensory stimuli. Our senses often receive conflicting multisensory information, which our brain reconciles by adaptive recalibration.
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