Skill Learning in Young Minimally-Verbal Children with Autism and the Effect of Vestibular Stimulation

Background: People with autism spectrum disorder (ASD), and especially the severe minimally-verbal individuals, often fail to learn basic perceptual and motor skills despite intensive repetitive practice. The reason for this learning deficit is currently unknown and overcoming it could have significant therapeutic implications. Previous findings suggest beneficial effects of vestibular stimulation in the normal, ADHD & LD populations, but the data regarding ASD are limited.

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

Methods: All children (N=39) 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 measure for learning was the median 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 session. Most children were also tested on a second sequence to examine the sequence-specificity of the learning gains.

Results: All groups showed a gradual median RT improvement with significant and similar speed gains across the training period (~150 ms, 15-30% of initial RT).  The ASD children (n=9) were overall slower (by ~300 ms), with initial intermittent pauses that required prompting to resume, but each individual child showed significant speed gains across the training days. Importantly, the ASD sub-group who received vestibular stimulation (n=5) had larger median speed gains compared to the other sub-groups (by ~100 ms), with a significantly larger effect observed when comparing the sequence trials with the fastest RTs (first decile values), which correspond to sub-sequence improvements. In comparison, vestibular stimulation had only a small or minimal effect on the non-ASD groups, but increased sequence-specificity of learning in all groups.

Conclusions: These results suggest that 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. Our current (limited) data also support the hypothesis of a positive effect of vestibular stimulation on learning in the severely autistic, which may have important therapeutic implications.  

We suggest that the difficulty of severely autistic children to learn even basic skills is not due to a primary deficit in procedural learning, but in the translation of explicit knowledge to procedures.