Object-Based Attention Modulation to Social and Nonsocial Stimuli In Children with Autism Spectrum Disorders

Background:  Autism spectrum disorders (ASD) are characterized by a triad of deficits, one of which is profound social impairment. Debate continues as to whether these social deficits arise from a specific inability to process social stimuli or a more general deficiency in complex information processing. A recent functional MRI (fMRI) study in our lab suggests the former; when compared to typically developing (TD) individuals, those with ASD showed reduced brain activation in response to social stimuli (faces), yet preserved activation to nonsocial stimuli (houses). Past fMRI studies, including one by Bird and colleagues (2006), provide further evidence of preserved nonsocial processing in adults with ASD. These past studies predominately used simple tasks manipulating spatial attention in adult participants. Few, if any, have examined the neural basis of preserved nonsocial object processing in children with ASD, or directly tested in children how attention differentially modulates brain activity in regions exhibiting category specific function.

Objectives:  Using fMRI we aim to investigate whether activation of the brain regions associated with faces and houses (social and nonsocial stimuli) in typical adults is modulated by implicit object-based attention in children with and without ASD.

Methods:  Adapting a study of object-based attention in adults from Kanwisher and colleagues (1999), subjects view an image of a face transparently superimposed over an image of a house. In alternating blocks, one image oscillates while the other remains static. Subjects are tasked with monitoring motion for a change in oscillation direction, without specific instruction to attend to which image is moving. Differential processing of face and house images can then be assessed by measuring BOLD signal from each participant’s fusiform face area (FFA) and parahippocampal place area (PPA), respectively.  Individual differences in symptom severity and social responsiveness are being assessed in participants to corroborate brain data.

Results:  Based on previous studies of object based attention in typical adults, we expect that in typically developing children object-based attention, even when implicitly directed, will modulate activity in the FFA during face processing and in the PPA during house processing. In children with an ASD, we expect typical modulation of PPA and reduced modulation of FFA. We also anticipate that the degree of modulation in the FFA will vary as a function of autism symptom severity in ASD and as a function of social responsiveness regardless of group membership. To date, preliminary results from three participants (2 TD, 1 ASD) are consistent with these predictions.

Conclusions:  The processes of perception and attention parse the world into discrete meaningful units.  Here we argue that impairments in ASD arise, at least in part, from deficits in these processes specifically for social stimuli.  By charting the patterns of neural activation to social and non-social stimuli in children with and without ASD, we can begin to better understand the nature of the unique constellation of deficits that we observe in ASD and begin to understand the basis of the observed heterogeneity in the disorder.