Motor dysfunction in Asperger's disorder: An analysis of timing, motor planning and visual perception of movement

Although motor deficits are presumed to be common in Asperger Syndrome (AS), the causes and characteristics of these deficits are unknown. This study addressed whether one or more of several variables discussed in the literature on Developmental Coordination Disorder, such as timing deficits, motor planning, and visual perception of movement, could account for clumsiness in AS. There were 14 AS participants (7 to 23 years old), and an age and gender matched group of 16 normal controls with no group IQ differences. Participants completed tests of timing perception and production, motor planning, visual perception of static forms, random moving dot kinematograms, biological motion, and postural stability in a moving virtual reality environment. Participants with AS were more erratic in their timing production, though there were no differences in the mean inter-response intervals of the two groups. There were also no differences in the perception of rhythms or in reaction time in responding to the perception task. Timing deficits therefore appear to implicate the motor system more than a central timing mechanism, and could be consistent with dysfunction within the extrapyramidal system. There were no group differences on a motor planning task, which may relate to the demands of the task. Participants with AS were less able to perceive biological motion, appearing less sensitive to normal movements than the control group, and less stable in virtually moving rooms, especially at the initiation of movement. While social experience could account for deficits in human movement perception, it could not account for hypersensitivity to virtual movement, potentially implicating abnormalities in the dorsal visual stream. Each of these group differences (i.e., timing variability, perception of biological motion, and stability in a virtual environment) was correlated with severity of motor deficits, measured using a clinical examination. The study is the largest to directly examine the components of motor dysfunction in a group of children with AS and also extends the age range into older adolescence, suggesting that motor dysfunction does not improve significantly with maturation into adulthood. Although a single causal factor is unlikely to accurately characterize motor deficits in AS, it is possible that the visual deficits could be the result of the interaction of the visual and motor systems, and that they may be a symptom, rather than a cause of motor dysfunction.