Review Multisensory Interplay Reveals Crossmodal Influences on 'sensory-specific' Brain Regions, Neural Responses, and Judgments Neural Studies of Multisensory Interactions: Traditional Focus on Multisensory Convergence Zones and Recent Findings on This Topic Converging Evidence from Single-cell Stu

Although much traditional sensory research has studied each sensory modality in isolation, there has been a recent explosion of interest in causal interplay between different senses. Various techniques have now identified numerous multisensory convergence zones in the brain. Some convergence may arise surprisingly close to low-level sensory-specific cortex, and some direct connections may exist even between primary sensory cortices. A variety of multisensory phenomena have now been reported in which sensory-specific brain responses and perceptual judgments concerning one sense can be affected by relations with other senses. We survey recent progress in this multisensory field, foregrounding human studies against the background of invasive animal work and highlighting possible underlying mechanisms. These include rapid feed-forward integration, possible thalamic influences, and/or feedback from multisensory regions to sensory-specific brain areas. Multisensory interplay is more prevalent than classic modular approaches assumed, and new methods are now available to determine the underlying circuits. Introduction Sensory processing and perception have been studied intensively for decades, in both neuroscience and psychology. But most traditional research considered just a single sensory modality at a time (e.g., vision or audition or touch). By contrast , real-world situations often stimulate several of our senses concurrently. Moreover, subsets of the incoming stimulation across different modalities arise from common external objects or events, as when we both see and feel an object in our hand or both see and hear a person talking or a car moving. In psychology, it has long been known that perceptual judgments can reflect combined information from multiple senses neuroscience has identified various ''multisensory'' brain regions as convergence zones, where neurons receive afferent inputs from several senses and combine these according to various constraints. But in recent years the field of multisensory research has expanded and altered radically with the realization that mul-tisensory influences are much more pervasive than classical views assumed and may even affect brain regions, neural responses , and judgments traditionally considered modality specific. Here we consider such cases, in which multisensory effects can arise for apparently sensory-specific processes or perceptions. We will often refer to multisensory ''interplay'' rather than the commonly used ''integration,'' so as to include cases where one modality might affect another without necessarily always implying a single unified percept. We focus primarily on human perceptual studies but refer to important animal work as relevant background. Behavioral and Perceptual Consequences of Multisensory Interplay in Humans Classic examples of multisensory perceptual ''illusions'' …