The emergence of multisensory systems through perceptual narrowing.

According to conventional wisdom, multisensory development is a progressive process that results in the growth and proliferation of perceptual skills. We review new findings indicating that a regressive process - perceptual narrowing - also contributes in critical ways to perceptual development. These new data reveal that young infants are able to integrate non-native faces and vocalizations, that this broad multisensory perceptual tuning is present at birth, and that this tuning narrows by the end of the first year of life, leaving infants with the ability to integrate only socio-ecologically-relevant multisensory signals. This narrowing process forces us to reconsider the traditional progressive theories of multisensory development and opens up several new evolutionary questions as well.