The Balance of Intended and Spontaneous Modes of Movement Control Is Atypical In Young Children with ASD

Background:  

There has been a recent focus on the importance of understanding movement abnormalities in Autism Spectrum Disorder (ASD) (Fournier, Hass, Naik, Lodha, & Cauraugh, 2010; Mostofsky et al., 2009; Dowell, Mahone, & Mostofsky, 2009). In natural movements of daily life, normal adults modulate transitions between intended (toward specific goals) and spontaneous (not explicitly goal-related) movements. These modes normally coexist in good balance. An unexplored question is whether this balance is disrupted in ASD. Here we asked if the spatio-temporal variability of movement trajectories under these two modes is different in children with ASD. The answer could provide insight into specific sensory-motor impairments in ASD.

Objectives:  

To quantify differences in the variability of spatiotemporal parameters from trajectories of natural movements performed in the classroom environment under intended and spontaneous modes of control.  

Methods:  

Children enrolled at the Douglass Developmental Disabilities Center (3-4 years of age) participated in this ongoing study, with 142 trials from TD children and 56 trials from children with ASD analyzed. Match-to-sample (e.g., color or shape) tasks common to the classroom curricula were used. Mousetracker software (Freeman & Ambady, 2010) displayed the tasks on a 21” touch-screen LCD monitor. On each trial the child’s task was to match (touch) the correct stimulus to one of two target locations on the touch-screen, initiating the movement by touching the starting location on the screen. Motion sensors were attached to the child’s hand, forearm, forehead, and trunk (Polhemus LIBERTY, 240Hz). Each session was videotaped (HD, 60Hz). Screen touches, video, and sensor data were synchronized and time stamped to determine intended movements towards the goal(s), correct responses, and to distinguish spontaneous movements in the continuous flow of motion.

Results:  

Temporal aspects of intended movements (goal-directed movements toward the screen) in TD children, but not in children with ASD, were significantly different than the temporal aspects of their spontaneous movements.  Specifically, the percentage of time to reach peak velocity and the percentage of time to reach maximal trajectory curvature were significantly different between the two modes of control for TD children but not for children with ASD.  Furthermore, the control of spontaneous movements was significantly different between groups according to a metric –proven effective in adults— that quantifies deficits in sensory-motor transformations (Torres et al, 2010). In contrast, spatial parameters (related to hand trajectory length and curvature) were not distinguishable between the two modes of control for either group.

Conclusions:  

The variability of the temporal dynamics of the movement trajectories in TD children is revealing of the mode under which each movement was performed. In contrast, the temporal dynamics of ASD trajectories cannot distinguish whether motions were intended or spontaneous. Our results suggest an imbalance between intended and spontaneous modes of control in children with ASD with a preponderance of movements of the type under study occurring in the spontaneous mode. Additionally, our objective metric suggests that the sensory-motor transformations that sub serve these two modes of control are likely atypical in children with ASD.