The development of multisensory facilitation for simple audio-visual information continues through adolescence.

Background. Significant variability characterizes the reported age ranges regarding the maturation or attainment of 'adult-like' ability for audio-visual (AV) multi-sensory integration (MSI). In part, this variability originates from diverse characteristics of unimodal audio and visual stimuli (e.g., social vs. non-social) used to assess MSI and the inconsistent developmental periods selected for cross-sectional evaluations. This study assessed the development of MSI for simple, non-social information from the early school-age years through to adulthood. Methods. One-hundred and eleven (n=111) neurotypical participants were placed into either child (6-9 ys, Mage=8.2), school-age (10-13 ys, Mage =12.0), adolescent (14-17 ys, Mage=15.0) or adult (18+ ys, Mage=22.7) age groups. Participants completed an audio-visual target detection task (Hershenson, 1962), presented with either a highly salient auditory (A) stimulus (beep), visual (V) stimulus (flash), or both stimuli at the same time (AV). Reaction times (RT) were recorded for a total of the 240 trials, with outliers (<100 or >1500 ms) excluded from analysis. Race Model analysis was conducted for each age group to compare audiovisual RTs with those expected from redundant stimuli, and a redundancy gain was calculated for each participant. Results. Increasing violations of the race model inequality as a function of age group were found, suggesting a progressive increase of AV multisensory facilitation for simple non-social information across developmental periods. Notably, the race model was violated through the 65th percentile of the RT distribution for the adolescent (14-17 ys) age group, which differed from that of the adult group (85th percentile). Conclusion. AV multisensory facilitation is not fully developed at adolescence, even when unimodal stimuli features are simple. This finding supports a later rather than earlier maturation period for AV MSI. These results also underscore the importance of including all development periods when assessing the development of AV MSI ability, including the adolescent age period.