Abstract
A number of recent studies on biological motion perception in people with autism have produced conflicting results with respect to the question whether biological motion perception is impaired in people with autism spectrum disorder (ASD) or not. We designed two experiments which probe two different aspects of biological motion and tested a group of 13 adult, high functioning people with autism as well as a group of age matched control subjects. The first experiment required observers to indicate whether a display showing a mask of scrambled walkers also contained a coherent walker or not. Solving this task requires the observer to perceptually organize the dots constituting the walker into a coherent percept. The second task required the observer to indicate perceived facing direction of a walker presented in sagittal view. In the critical condition, the walker was scrambled. Solving this task requires intact processing of the cues contained in the local motion of individual dots which signals direction and animacy to normal observers. In both experiments, stimuli were shown both upright and inverted and the degree of the inversion effect which observers experience was quantified. In both tasks, human and non-human (cat, pigeon) walkers were employed. Results reproduced general effects of inversion, masking, and the nature of the walker, all of which have been shown earlier. However, they did not reveal any main group effect nor any interactions that involved the between-subject factor. In both experiments, the overall performance, the degree of the inversion effect, the sensitivity to mask density, and differences in the processing of human vs. non-human walkers were the same between the two groups. However, for the ASD group, in the direction task, we found a significant positive correlation between subjects' IQ and overall performance and a negative correlation between subjects' IQ and sensitivity to stimulus inversion.