Global Motion Perception in ASD: A Meta-Analysis

Background: Visual perception in individuals with autism spectrum disorder (ASD) is often characterized by enhanced perception of local elements and impaired perception of global patterns. Deficits in global motion perception, mostly coherent motion and biological motion, seem to support this characterization, although the evidence is inconsistent. A proper quantitative review of the available data, in which the overall effect size of each study is assessed and the influence of potential moderators is investigated, is lacking. Yet, it is of critical importance to understand performance of global motion in order to evaluate theories of perception in ASD.

Objectives: To evaluate all experimental data on global motion perception, and (a) assess whether the available data are in favor of the hypothesis of enhanced perception of local elements or the hypothesis of impaired global perception in individuals with ASD compared to typically developing controls, and (b) evaluate which moderator variables rule the diversity within the literature.

Methods: A large meta-analysis was conducted, combining 48 articles on biological motion and coherent motion, including approximately 1,000 individuals with ASD and controls. All data were coded and transformed to the standardized mean difference metric d and used in a linear three-level random effects model, accounting for random sampling fluctuation, between-outcome variance and between-study variance. Differences in paradigm, task, stimulus and participant characteristics were taken into account and evaluated as potential moderators.

Results: The results revealed a small mean effect of -0.30, with 95% confidence limits from -0.17 to -0.44, indicative of global motion processing difficulties in ASD. This mean negative effect was apparent for both biological motion as well as coherent motion paradigms, and appeared to be independent of the paradigm, task, dependent variable, age or IQ of the groups.

Conclusions: The results of our meta-analysis indicate that individuals with ASD are less sensitive to global motion perception, as present in both coherent motion and biological motion paradigms. However, the differences in neural mechanisms that might underlie this behavioral difference remain unclear. Recommendations for future motion research are made in the hope of refining current theories on vision in ASD and atypical development in general.