A comparison of constrained and unconstrained reaching movements by people with and without autism spectrum disorders


Although not included in the definition of Autism spectrum disorder (ASD), motor performance differences are reported consistently. Specifically, individuals with ASD spend more time preparing movements. Currently there is a debate as to whether people with ASD require more time to execute reaching movements. The present study compared constrained and unconstrained reaching movements in order to determine if previous reports of a preference for proprioceptive feedback explains inconsistent movement time reports in the literature. Eleven ASD participants and 13 typically developing (TD) participants were recruited. All participants performed three types of reaching movements in the sagittal plane: 1) sliding along a track on a piece of Plexiglas (1D, constrained); 2) sliding along a smooth piece of Plexiglas (2D, constrained); and 3) aiming movements (3D, unconstrained). Movements were recorded using a 3D motion analysis system (3D Investigator, NDI) and muscle activity was recorded using surface electromyography (CED 1902 dual system amplifier). All dependent variables were submitted to a 2 Group (ASD, TD) by 3 Movement Type (1D, 2D, 3D) mixed analysis of variance. Results revealed a significant Group by Movement Type interaction for premotor reaction time, movement time, and time after peak velocity. The ASD group took longer to prepare and execute 3D (unconstrained) movements compared to the TD group. The current findings are consistent with previously reported behavioral and brain imaging research identifying altered brain connections in ASD participants indicative of a preference for haptic over visual feedback for movement control.

Acknowledgments: Funding: Research Manitoba; The present research was also made possible by funding from the Canadian Foundation for Innovation. The authors would like to thank Kelsey Brown and Brie Page for their help collecting data and all of the participants for their time.