A physiological assessment of lateral interactions within the early visual areas of adults with ASD

by Sabrina Censi

Institution: McGill University
Department: Department of Educational and Counselling Psychology
Degree: MA
Year: 2015
Keywords: Education - Psychology
Record ID: 2057970
Full text PDF: http://digitool.library.mcgill.ca/thesisfile130372.pdf


Background The importance of early perceptual alterations with regards to higher-level perceptual and cognitive functioning in Autism Spectrum Disorder (ASD) is increasing. This increase is due in part to several studies demonstrating altered autistic sensitivity to a variety of non-social visual, auditory and tactile stimuli whose perception is contingent on the functional integrity of early, local neural mechanisms. However, although atypical performance on non-social, visuo-spatial tasks is a defining characteristic of ASD, few biologically plausible hypotheses are available to explain them. Some have theorized that individuals with ASD may have atypical local connectivity resulting in altered response properties of early visual feature detectors, such as those processing simple visual patterns. The goal of these studies was to assess this hypothesis by measuring brain activity to simple visual information that is mediated by local, lateral interactions. To do so, steady-state visual evoked potentials (ssVEPs) to visual information mediated by lateral connectivity was measured in a group of adults diagnosed with ASD.MethodsNine participants with ASD and 11 typically developing participants, matched for full-scale IQ and age (18-35 years), were asked to passively view visual stimuli during Windmill-Dartboard (Ratliff & Zemon, 1982) and lateral masking paradigms (Polat, Sagi, & Norcia, 1997) while ssVEPs from four electrodes over the occipital cortex (Oz, POz, O1 and O2) were collected. For the Windmill-Dartboard paradigm, first- and second-harmonic components of the steady-state responses were used to calculate indices reflecting local facilitatory (FI) and inhibitory (SI) cortical interactions for all participants. For lateral masking paradigm, ssVEP data was collected while participants viewed low-contrast Gabor patches presented ether in isolation (target), or flanked by collinear/orthogonal Gabors at different contrasts (8, 16, 30%) and target-flanker distances (1.5λ, 3 λ, 6 λ). ResultsGroup differences were not evidenced for either FI or SI cortical interaction indices obtained during the Windmill-Dartboard task. For the lateral masking paradigm, the results demonstrated between group differences in lateral interactions under specific experimental conditions. There were statistically significant facilitatory responses at a distance of 3λ, for both the ASD (at a contrast of 30%) and comparison group (at a contrast of 8%). However, only the comparison group demonstrated statistical significance of a suppression response at a contrast of 16%. In addition, only the comparison group demonstrated statistical significance of a suppression response at a contrast of 16% at a distance of 6 λ. ConclusionThe current studies attempted to directly examine lateral interactions by measuring steady-state visual evoked potentials (ssVEPs) elicited by Windmill-Dartboard and lateral masking paradigms. A lack of between group differences in ssVEP responses elicited by the Windmill-Dartboard task suggests unremarkable local…