The End-State Comfort Effect in Children with Autism Spectrum Disorder and Typically Developing Children: The Importance of Functionally Relevant Motor Tasks

Background:  The end-state comfort effect occurs when one adopts an initially uncomfortable posture during a movement sequence in order to attain a comfortable posture at the completion of object manipulation, thus demonstrating motor planning (Rosenbaum et al., 1990). For example, one may grasp a key with an awkward underhand grip, so that a comfortable hand position is achieved after the key is rotated in the lock. Previous studies suggest that children and adolescents with Autism Spectrum Disorder (ASD) do not exhibit the end-state comfort effect (Hughes, 1996; Simermeyer & Ketcham, 2015), but it is unclear whether these motor impairments generalize from lab tasks to more functional types of motor behaviors.

Objectives:  To determine if the end-state comfort effect is demonstrated in children with ASD compared to children with typical development (TD) in both the traditional paradigm and a more functional task.

Methods:  Twenty-one participants with ASD and 16 age-matched TD participants (ages 6-17 years, p=.76) completed a traditional dowel task and a more functionally relevant task which required them to use a mallet to hammer a peg. In the dowel task, participants were instructed to grasp a horizontally positioned dowel and touch one end to a target positioned to the left or right. The ends of the dowel and the targets were different colors so that participants understood the directions (e.g., touch the blue end of the dowel to the red target). Each condition was repeated twice. In the mallet task, participants were instructed to use the mallet to tap a peg to the left of the stand holding the mallet. Initially, the head of the mallet was positioned to the participant’s right or left side. Each condition was repeated four times and the tasks were counter-balanced. In both tasks, two researchers live coded whether the participant used an overhand or underhand grasp to complete the task. A two-way repeated-measures ANCOVA with group as the between-subjects factor, task as the within-subjects factor, and age as a covariate was used to test the percentage of trials completed in accordance with end-state comfort.

Results:  The two groups did not differ in the percentage of trials completed in accordance with the end-state comfort effect for either task. There was a significant effect of task, with the mallet task (M=88.5) having a higher percentage of comfortable end-state positions compared to the dowel task (M=65.1) (p=.001). This result suggests that both children with ASD and with typical development demonstrate a greater degree of motor planning when the task has functional relevance. There was a trend toward a higher percentage of comfortable end-state positions in the dowel task with increasing age (r=.30, p=.07).

Conclusions:  Participants with ASD did not differ from their TD peers in the percentage of movement sequences performed in accordance with the end-state comfort effect. This is in contrast to previous work but suggests the ability to plan motor sequences. The results of this study emphasize the importance of using functional tasks when evaluating motor planning in children with and without autism.