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Thursday, May 15, 2008
Champagne Terrace/Bordeaux (Novotel London West)
10:30 AM
Background: Increasing evidence show atypical visual processing in autism; this pattern of atypical performances has lead to the development of neurobehavioral theories of autism describing these anomalies as consequences of an abnormal multimodal structure of information in the visual modality. Objectives: To explore motion-coherence and form-coherence processing in Asperger’s disorder (AS) using psychophysics and fMRI and to examine whether morphological differences are related to regions of altered activation.
Methods: We measured form and motion thresholds for detecting a Glass stimulus of varying coherence in a field of random dots in a group of adults diagnosed with Asperger’s syndrome and a normal control group matched for chronological and mental age. A coherent visual patch was depicted by dots separated by a rotational transformation in space (form coherence) or space-time (motion coherence). Stimuli were presented for 0.25s to prevent serial search strategies. Coherence was progressively reduced from 1.0 until an error was made, in the manner of a 2-up, 1-down staircase. In a parallel event-related fMRI study, participants performed the same task in the scanner at fixed coherence levels (0, 0.125, 0.25, 0.5, 1.0). Voxel-based Morphometry (VBM) was implemented to compare structural differences between the two groups.
Results: Results from the psychophysical and fMRI data showed that adults with AS perform at the same level as controls in motion processing, replicating previous studies with children. However, it was found for the first time that individuals with Asperger’s show lower form coherence thresholds. In addition, increased fMRI BOLD responses to form coherence in the middle occipital gyrus, the intraparietal sulcus and the ventral surface were reported in the AS group. VBM indicated significantly higher levels of global grey matter density in Asperger.
Conclusions: The results represent a contribution towards better understanding of the mechanisms mediating visual information processing in autistic spectrum disorders.
Methods: We measured form and motion thresholds for detecting a Glass stimulus of varying coherence in a field of random dots in a group of adults diagnosed with Asperger’s syndrome and a normal control group matched for chronological and mental age. A coherent visual patch was depicted by dots separated by a rotational transformation in space (form coherence) or space-time (motion coherence). Stimuli were presented for 0.25s to prevent serial search strategies. Coherence was progressively reduced from 1.0 until an error was made, in the manner of a 2-up, 1-down staircase. In a parallel event-related fMRI study, participants performed the same task in the scanner at fixed coherence levels (0, 0.125, 0.25, 0.5, 1.0). Voxel-based Morphometry (VBM) was implemented to compare structural differences between the two groups.
Results: Results from the psychophysical and fMRI data showed that adults with AS perform at the same level as controls in motion processing, replicating previous studies with children. However, it was found for the first time that individuals with Asperger’s show lower form coherence thresholds. In addition, increased fMRI BOLD responses to form coherence in the middle occipital gyrus, the intraparietal sulcus and the ventral surface were reported in the AS group. VBM indicated significantly higher levels of global grey matter density in Asperger.
Conclusions: The results represent a contribution towards better understanding of the mechanisms mediating visual information processing in autistic spectrum disorders.