| Social dysfunction is a hallmark feature of Autism Spectrum Disorder (ASD). However since the initial description of ASD by Kanner (1943) it has been recognized that the disorder may manifest from a more basic neuropsychological deficit in attention and/or arousal, and previous studies have found altered autonomic and attentional responses during both baseline conditions and in response to socially-relevant stimuli in those with ASD. Based on this line of inquiry, we recently used eye-tracking technology to examine visual scanning and pupillary responses and found a larger tonic (baseline) pupil size (Anderson & Colombo, 2009) and altered phasic (task-specific) pupillary responses to human faces, with no group-based differences in visual scanning (Anderson, Colombo, & Shaddy, 2006) in 2-5 year old children with ASD compared to age-matched controls. To replicate and extend these previous results, children (20 -- 72 months of age) with ASD (n = 12), along with Down syndrome (DS; n = 9), and typicallydeveloping (TD; n = 11) age-matched controls were presented with a social and a non-social dynamic and multimodal video clip. Each stimulus was presented for 10 minutes on two separate testing days; location of gaze and pupil size was recorded, along with salivary measures of alpha-amylase and cortisol. Tonic measures of pupil size, AA and cortisol were also recorded during a baseline period. The ASD group was significantly distinguished in group-based analyses from both the DS and TD groups through (a) a larger tonic pupil size, (b) lower tonic levels of AA, which were significantly related to tonic pupil size, and (c) increased phasic pupil responses to the social stimulus. These findings provide replication of our previous investigations and a unique finding of lower AA levels in the ASD group. These results may provide clues about underlying norepinephrine system pathology in ASD, and the potential of non-invasive measures of pupil size and salivary AA in the early identification and screening of the disorder. |
