The present study investigated the intersensory processing deficit for social stimuli in individuals with ASD compared to age- and cognitive-ability matched typically developing peers. This deficit was theorized to account (at least partially) for cascading impairments in attention and autism symptomatology across development. The primary goal was to isolate the social and linguistic properties of intersensory (audio-visual) processing using a manipulation of temporal synchrony. In Study One, a multi-method analysis of looking time and proportion of efficient gaze patterns using eye-tracking data from a behavioural task was used. Results provided evidence of a difference in intersensory processing specifically for social stimuli in children with ASD that does not appear to be solely attributable to a deficit in processing faces, language, or body movement. The secondary goal of the project was to provide a better understanding of variables that impact and are impacted by intersensory processing. In Study Two the strength and direction of the relationship between intersensory processing and developmental, diagnostic, and attention variables was assessed. Results showed that impaired intersensory processing for social information appears to be associated with cascading consequences across development including some of the core impairments in Autism Spectrum Disorder: disrupted sensory processing, social-communication disability, and slower attentional disengagement. In summary, results of Study One and Study Two are best understood as a specific cognitive-perceptual deficit in social orienting and are consistent with the Intersensory Redundency Hypothesis. The observed intersensory processing differences between groups may be impacted by dysfunctional intersensory integration wherein the most general amodal property, temporal synchrony, is misprocessed at early stages, disrupting selective attention and early social orienting. This impairment impacts the cascading cycle of perception, learning, memory, attention and so on and contributes to core sensory and social-communication impairments associated with Autism Spectrum Disorder.