Lateral Masking Paradigms Reveal Atypical Interactions in Autism

Background: Bertone et al. (2005) demonstrated that autistics were superior to nonautistics in identifying the orientation of static gratings consisting of simple, luminance-defined information. However, autistics were inferior when the gratings consisted of complex, texture-defined information. These authors suggested that the most biologically plausible type of neural alteration congruous with this dichotomous performance was strong or enhanced lateral inhibition, a type of lateral connectivity within the primary visual cortex that mediates the extraction of low-level static information.

Objectives: This study aimed at assessing the hypothesis of atypical lateral connectivity in autism using lateral masking paradigms (Polat & Sagi, 1993). In such paradigms, the sensitivity of a centrally presented Gabor target stimulus is affected by lateral (or flanking) stimuli presented simultaneously at certain distances from the target. This lateral interaction is dependent on different variables, including target/flanker distance (Polat & Sagi, 1993) and the contrast of the flanking stimuli (Yu et al., 2002).

Methods: 10 autistic and nonautistic participants matched for chronological age (mean of 22 years), full-scale IQ, gender and handedness completed the experimental tasks. Detection thresholds for vertically oriented target Gabor stimuli were measured alone (no flanker condition), and with same-orientation flanking stimuli presented above and below at two different distances (3 and 6 lambda). In an additional condition, the distance between the target and flankers was set at 3 lambda; the contrast of the flankers (presented orthogonal to the target) was varied from 0.05, 0.1, 0.2, 0.4 and 1. Target detection thresholds in both conditions were measured using an adaptive staircase procedure.

Results: As expected, both groups showed facilitation at 3 lambda (increased sensitivity to target) in Experiment 1. However, a relatively greater facilitation was demonstrated by the autistic participants. No between-group difference was found for the 6 lambda condition. Manipulating the contrast of the flankers did not result in between-group differences.

Conclusions: The findings from this study represent behavioral evidence for atypical lateral connectivity (i.e. excessive lateral inhibition) mediating spatial information processing within early visual areas in autism.  It is suggested that the behavioral consequence of this neural hypothesis (either enhanced or diminished sensitivity to static stimuli), is dependent upon the physical attributes defining the information being analyzed (Vandenbroucke et al., 2008).