17404
Assessing Lateral Interactions within the Early Visual Areas of Adults with Autism
Although atypical performance on visuo-spatial tasks targeting early, non-social perception is a defining characteristic of autism, few biologically plausible hypotheses are available to explain them. Some authors have theorized that persons with autism may have atypical local connectivity resulting in altered response properties of early visual feature detectors (Vandenbrouke et al 2008; Keita et al 2011). One manner to assess such hypotheses is to measure and define local neural activity originating from lateral interactions within early visual areas. This can be done by measuring steady-state visual evoked potentials (ssVEPs) elicited during visual stimulation that specifically targets lateral cortical interactions. One such stimulation is exemplified by the windmill-dartboard paradigm (Ratliff & Zemon, 1982), which consists of a radial pattern comprising concentric contrast reversing zones with contiguous static zones. The varying contrast at the borders of contiguous static and dynamic segments of the windmill-dartboard stimulus result in highly localized lateral interactions (Ratliff & Zemon, V, 1982). In addition, lateral masking paradigms - where low-contrast Gabors are presented either in isolation (target), or flanked by collinear/orthogonal Gabors at different contrasts and target-flanker distances - can also be used measure lateral cortical interactions (Polat et al, 1997).
Objectives:
The objective of this study was to systematically assess lateral interactions between neurons within early visual areas in autism by measuring steady-state visual evoked potentials (ssVEPs) elicited by (i) windmill-dartboard and (2) lateral masking paradigms.
Methods:
Nine participants with autism and 9 typically developing participants, matched for full-scale IQ and age (18-30 years), were asked to passively view visual stimuli during windmill-dartboard and lateral masking paradigms 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 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%) at target-flanker distances (1.5λ, 3 λ, 6 λ).
Results:
Group differences were not evidenced for either FI or SI cortical interaction indices obtained during the windmill-dartboard task. For the lateral masking paradigm, an expected difference between collinear and orthogonal Gabors (presented at a contrast of 16%) at target-flanker distances of 1.5 λ was found in the control group, p= 0.018. Importantly, this difference was not evidenced for the autism group.
Conclusions:
Our results to date measured using the windmill-dartboard paradigm suggest that facilitatory (FI) and inhibitory (SI) cortical interactions within early visual brain areas are similar in autism and control groups. However, group differences on the lateral masking paradigm are consistent with the hypotheses that lateral connectivity within early visual areas is atypical in autism, and may be considered a possible early neural origin for altered perception in autism.