Autism spectrum disorders (ASDs) are developmental disorders which are thought primarily to affect social functioning. However, there is now a growing body of evidence that unusual sensory processing is at least a concomitant and possibly the cause of many of the behavioural signs and symptoms of ASD. A comprehensive and critical review of the phenomenological, empirical, neuroscientific and theoretical literature pertaining to visual processing in ASD is presented, along with a brief justification of a new theory which may help to explain some of the data, and link it with other current hypotheses about the genetic and neural aetiologies of this enigmatic condition.

When we observe someone perform a familiar action, we can usually predict what kind of sound that action will produce. Musical actions are over-experienced by musicians and not by non-musicians, and thus offer a unique way to examine how action expertise affects brain processes when the predictability of the produced sound is manipulated. We used functional magnetic resonance imaging to scan 11 drummers and 11 age- and gender-matched novices who made judgments on point-light drumming movements presented with sound. In Experiment 1, sound was synchronized or desynchronized with drumming strikes, while in Experiment 2 sound was always synchronized, but the natural covariation between sound intensity and velocity of the drumming strike was maintained or eliminated. Prior to MRI scanning, each participant completed psychophysical testing to identify personal levels of synchronous and asynchronous timing to be used in the two fMRI activation tasks. In both experiments, the drummers' brain activation was reduced in motor and action representation brain regions when sound matched the observed movements, and was similar to that of novices when sound was mismatched. This reduction in neural activity occurred bilaterally in the cerebellum and left parahippocampal gyrus in Experiment 1, and in the right inferior parietal lobule, inferior temporal gyrus, middle frontal gyrus and precentral gyrus in Experiment 2. Our results indicate that brain functions in action-sound representation areas are modulated by multimodal action expertise.

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