Stimulus value gates multisensory integration

The brain enhances its perceptual and behavioral decisions by integrating information from its multiple senses in what are believed to be optimal ways. This phenomenon of "multisensory integration" appears to be pre-conscious, effortless, and highly efficient. The present experiments examined whether experience could modify this seemingly automatic process. Cats were trained in a localization task in which congruent pairs of auditory-visual stimuli are normally integrated to enhance detection and orientation/approach performance. Consistent with the results of previous studies, animals more reliably detected and approached cross-modal pairs than their modality-specific component stimuli, regardless of whether the pairings were novel or familiar. However, when provided evidence that one of the modality-specific component stimuli had no value (it was not rewarded) animals ceased integrating it with other cues, and it lost its previous ability to enhance approach behaviors. Cross-modal pairings involving that stimulus failed to elicit enhanced responses even when the paired stimuli were congruent and mutually informative. However, the stimulus regained its ability to enhance responses when it was associated with reward. This suggests that experience can selectively block access of stimuli (i.e., filter inputs) to the multisensory computation. Because this filtering process results in the loss of useful information, its operation and behavioral consequences are not optimal. Nevertheless, the process can be of substantial value in natural environments, rich in dynamic stimuli, by using experience to minimize the impact of stimuli unlikely to be of biological significance, and reducing the complexity of the problem of matching signals across the senses.