Simple Reaction Time Performance in Autism Spectrum Disorder and Neurotypical Subjects

Background: The speed with which an individual is able to make a simple motor response to a perceived stimulus may fairly be regarded as a significant index to his basic level of perceptual-motor integration. Developmental studies on reaction time in subjects with a neurotypical (NT) development report a decrease in simple reaction time (SRT) with increasing age and a strong correlation between upper and lower limb simple reaction time tasks. No studies are available in this regard in Autism Spectrum Disorder (ASD) subjects.

Objectives: The aims of this study are: 1) to assess developmental changes in the speed of a simple reaction at the lower and upper limb in ASD children as they age; 2) to assess the correlation between upper and lower limbs SRT in ASD children; 3) to assess the correlation between lower limb SRT and ankle dorsiflexors muscles strength in ASD children; 4) to compare the results with the same data obtained in a sample of 243 NT subjects.

Methods: The study sample included 12 ASD subjects (10 males; age range 5 -18 years). The ASD subjects were diagnosed with autism according to the DSM V criteria, confirmed through ADOS-2 and under observation at our Institute. SRT was measured in milliseconds using a hand-held electronic timer and a light as the stimulus and finger or foot lever to trigger responses. The testing of ankle dorsiflexion force was done using a footplate attached to a spring gauge. All the tests employed have been validated for the study of sensorimotor components of balance into the Fall Screen Assessment System.

Results: At variance with NT group we found no significant correlation between both upper and lower SRT and age in ASD study group (upper limb: R Pearson=-0.056, p=0.863; lower limb: R Pearson=-0.065, p=0.841) and no correlation between lower limb SRT and ankle dorsiflexors muscles strength. Instead, similarly to NT group a significant positive correlation between upper and lower limb reaction time tasks was found (ASD: R Pearson=0.819, p=0.001; NT: R Pearson=0.666; p=0.000).

Conclusions: This is the first study that analyses upper and lower limbs SRT developmental variability and its correlation with ankle strength performance in ASD subjects. The absence of a developmental improvement in SRT and the impairment in lower limb SRT tasks found in ASD subjects point out a disorder of sensorimotor integration in ASD subjects potentially responsible for postural control imbalance.