Development of Audiovisual Integration in Human Infants: The Effects of Spatial and Temporal Congruency and Incongruency on Response Latencies

Every day we are inundated with a mass of sensory inputs providing a continual stream of relevant and irrelevant, redundant and conflicting, information about the external world. Mature brains are very capable in integrating this confusion of input into a unified percept, but this is a non-trivial task for infants, whose brains and sensory systems are still immature at birth and who rely on their current level of integration and interaction of these inputs in order to shape their future development. Failure in being able to properly process basic sensory interactions has been implicated in higher-level developmental problems like attentional or autistic spectrum disorders. Numerous studies have looked at how adults perceive and react to multisensory stimuli, including findings of improved response latencies and target detection for spatially and temporally congruent stimuli, but much less is known about the development of multisensory integration or how spatial or temporal disparities effect sensory interactions in young babies. We examined the role of spatial and temporal congruency and incongruency on the response latencies of infants under ten months of age orienting toward an audiovisual stimulus at +/-25 degrees and/or +/-45 degrees. In Study 1, we found the beginnings of adult-style non-linear integration for spatially and temporally congruent audiovisual targets in 8–10 month olds, but not in younger infants, as well as indications of a differential developmental profile for binaural versus monaural processing. In Studies 2 and 3, spatial and temporal disparities were found to significantly lengthen infants’ response latencies to an audiovisual target. We also found clear indications of developmental changes for all three spatial and temporal conditions, as well as key dependencies in relative position, temporal order, and sensory dominance