Atypical Patterns of Motor Variability and Error Correction In ASD Individual Performing Repetitions of Complex Movements

Background: One element of the behavioral triad used to diagnose Autism Spectrum Disorder (ASD) is the presence of restricted and repetitive behaviors (APA, 2000). In experimental settings, during the repetition of intended movements, natural movement variability has been shown to contribute to error correction, which is important for the adjustment of upcoming movements (van Beers, 2010). Less is known about the variability of spontaneous, non-goal directed movements. Our goal is to analyze movement variability and transitions between intended and spontaneous movements during repetitive behaviors in ASD. We compared the movement variability of a martial arts expert, 5 novices and 1 individual with ASD as they performed a complex white belt routine that alternated between segments under intended control (overtly attended to) and simultaneous segments of spontaneous motion (covertly attended to). First we established the “ground truth” (expert performance) as a basis for comparison, then we determined differences between normal controls and the ASD individual.

Objectives: We seek to determine if the ASD system uses movement variability in the same way as the typically-developing system does to correct errors during repetitions of the same movement.

Methods: The white belt routine (Jab-Cross-Hook-Uppercut) was performed at 2 different speeds (normal-to-slow and fast). Full-body movements were recorded using 16 electro-magnetic sensors (240 HZ each) attached to the head, to various points of the trunk, arms, and legs (Motion Monitor, Polhemus LIBERTY) and 2 video cameras (HD, 60Hz) for further video frame analysis. The sensors output the rotations and positional displacements in physical space of each point of the body at the sensor locations. Each one of the 4 subroutines was first performed individually (10 trials each speed) and then in combination (10 trials each speed).

Results: Expert performance revealed that for simultaneous control of two or more limbs, the system funnels attention to one limb at a time. As the trajectory of the overtly attended limb unfolded, the trajectory of the other limb—which transitioned to another subroutine—was covertly attended to. This was evidenced by the different effects of speed on the movement variability of the two segment types. Segments that were overtly tended to maintained low variability and conserved the physical curve; whereas, segments that were simultaneously performed and covertly attended to qualitatively changed their trajectories with speed. Trial-to-trial variability revealed that the expert system used error from previous movements to correct future movements. Relative to the expert, the normal novices maintained the same trend. The ASD individual on the other hand, performed differently. Variability in this case was lowered by locking degrees of freedom (DOF) at the expense of atypically large variability in the remaining DOF. Unlike the typical controls, speed had a large effect on the intended trajectories of the ASD individual, which did not conserve the physical path of the movements from the segments that required overt attention.

Conclusions: During error correction of consecutive trials, the ASD system uses movement variability differently than the normal system. These analyses may be useful to quantify aspects of repetitive behavior in ASD.