Dept of Psychology
UC San Diego
Intermingling of Sensory Representations over the Course of Development
Abstract. Early infancy is characterized by a period of exuberant neural connectivity followed by a retraction and reweighting of connections over the course of development. It has been proposed that this connectivity may produce a perceptual intermingling of the senses in infants that is unlike that experienced by typical adults. And, a lack of pruning of these exuberant connections during development is thought to explain the rare condition of “synesthesia” in about 2% of adults, wherein one sense involuntarily evokes an additional arbitrary sensation. We have been studying the perceptual consequences of neuronal intermingling in young infants and adults with “grapheme-color” synesthesia, wherein specific letters or numbers evoke idiosyncratic, largely individualized sensations of specific colors. Our results in typically developing infants (2 to 4 months) are consistent with them making strong associations between color and shapes (a precursor to graphemes), as well as between color and motion, which are significantly greater than the associations experienced by typical adults. Such findings – which suggest that all young infants experience synesthesia, provide a perceptual consequence of the exuberant neural connections seen in the infant brain. This talk will also present data from studies in adult grapheme-color synesthetes. Here, our results suggest that the exuberant intermingling of color and grapheme representations in synesthetes comes at the expense of connections between color and other aspects of vision, specifically, motion. We also find that adult grapheme-color synesthetes discriminate colors better than controls, which we suggest may arise from “bi-directionality”, whereby colors elicit an additional experience of graphemes that aid in color discrimination. This heightened color sensitivity could help explain why synesthesia has survived in evolution.