Visual cortex signals a mismatch between regularity of auditory and visual streams

Understanding how humans code for and respond to environmental uncertainty/regularity is a question shared by current computational and neurobiological approaches to human cognition. To date, studies investigating neurobiological systems that track input uncertainty have examined responses to uni-sensory streams. It is not known, however, whether there exist brain systems that combine information about the regularity of input streams presented to different senses. We report an fMRI study that aimed to identify brain systems that relate statistical information across sensory modalities. We constructed temporally extended auditory and visual streams, each of which could be random or highly regular, and presented them concurrently. We found strong signatures of "regularity matching" in visual cortex bilaterally; responses were higher when the level of regularity in the auditory and visual streams mismatched than when it matched, [(AudHigh/VisLow and AudLow/VisHigh) > (AudLow/VisLow and AudHigh/VisHigh)]. In addition, several frontal and parietal regions tracked regularity of the auditory or visual stream independently of the other stream's regularity. An individual-differences analysis suggested that signatures of single-modality-focused regularity tracking in these fronto-parietal regions are inversely related to signatures of regularity-matching in visual cortex. Our findings suggest that i) visual cortex is a junction for integration of temporally-extended auditory and visual inputs and that ii) multisensory regularity-matching depends on balanced processing of both input modalities. We discuss the implications of these findings for neurobiological models of uncertainty and for understanding computations that underlie multisensory interactions in occipital cortex.