Vestibular Stimulation Improves Skill Learning in Minimally Verbal Children with ASD: A Comparative Study with ADHD and Typical Controls

Background: ASD and ADHD children share many symptomatic characteristics, such as deficits in sensory processing, attention and learning. All these may jeopardize motor skill learning, especially in the severe minimally-verbal individuals with ASD, who often fail to learn basic perceptual and motor skills for unknown reason. In the current study, we sought to characterize the skill learning deficit in ASD in comparison with ADHD and explore ways for improvement. Previous findings suggest beneficial effects of vestibular stimulation on sensory processing, attention and learning in the typical & ADHD populations, but the data regarding ASD are limited. Preliminary results from this study were reported in IMFAR last year, while the current report extends and consolidates the previous findings. 

Objectives: To investigate the evolution in time of skill (sequence) learning and the modulatory effect of vestibular stimulation, in 3 groups of children ages 6-13, comparing minimally-verbal ASD with ADHD and typical development (TD) children.

Methods: All children (N=45) were trained on a touch version of the cognitive related visual-motor SRT task, with 10 short (<300 trials, few minutes) weekly practice sessions. In the task, a fixed sequence of 12 spatial locations, cyclically repeated 8 times in each block of trials, was introduced via visual cues on a touch tablet. The responses were made by rapidly touching the cued location with a finger, thus, unbeknown to the children, the cues introduced a sequence of lateral movements to be learned. The measures for learning were the median and the mean of the series response-time (RT). Each group was divided into two sub-groups, one of which received a vestibular stimulation prior to each training block.

Results: All groups showed gradual median RT improvement (Figure A) with significant speed gains across the training period. The ASD children (n=18) were overall slower (by ~200 ms), with initial intermittent pauses that required prompting to resume. Importantly, the ASD sub-group who received vestibular stimulation (n=10) had significantly larger median speed gains and fewer long pauses in comparison to ASD controls. Vestibular stimulation had no effect on TD and had a small reversed effect on the ADHD group.

Conclusions: These results suggest that vestibular stimulation has a positive effect on learning in minimally-verbal children with ASD, which may have important therapeutic implications. Furthermore, contrary to some previous findings, minimally-verbal children with ASD can acquire and consolidate procedural skills with few short training sessions, spread over weeks, and with a similar time course as non-ASD controls. We suggest cortical arousal as a possible mediating variable, explaining the vestibular effect. For the ADHD group, the lack of positive vestibular effect could be attributed to the short and non-demanding practice sessions we used.  For the ASD group, increased arousal may overcome their known deficits in disengagement and reorienting of attention and enhance sequence learning.