The Relationship Between Motor Demands and Processing Speed In High Functioning Children with Autism Spectrum Disorders

Background: Wechsler Processing Speed Index scores are impaired in children with autism spectrum disorders (ASD); however, when motor demands are removed and pure speed of processing is assessed using the “Inspection Time” (IT) task there is an advantage for lower functioning children with ASD relative to IQ-matched peers with developmental delays. There are two possible explanations for this discrepancy; one is that the ASD IT advantage only exists for low functioning children with ASD, not the higher functioning children typically studied with the Wechsler Processing Speed Index. Another explanation is that significant speeded motor output demands of the Wechsler Processing Speed subtests, not mental speed of processing, are what impairs performance in ASD. We are not aware of any study that has manipulated motor demands within the IT paradigm.  

Objectives: Examine IT in a sample of high functioning children with ASD and explore the impact of varying motor demands on processing speed. We predicted intact performance on the original IT task, but worse performance in the ASD group as motor demands are increased.  

Methods: 27 school-aged children (TD, N=9, FSIQ=117.89; ASD, N=18, FSIQ=111.72) were recruited for research studies conducted at Children’s National Medical Center. Participants were matched for IQ, age, and gender. Four additional participants were excluded from analyses because their performance was over 2.5 standard deviations from the mean. Three versions of IT that assess processing speed while progressively manipulating the complexity of the required motor response were administered. In the standard IT version, which has no speeded motor demands, children viewed an alien spaceship with antennae that were either the same or different length. They saw the spaceship for a brief time period, ranging from 18ms to 300ms and were given an unlimited amount of time to indicate whether the antennae were same or different lengths. In the low motor demand version, children viewed the spaceship’s antennae until they made a simple timed button response. In the high motor demand version, children physically drew their response lines of same and different lengths – this version was thought to imitate standard processing speed measures from IQ tests. Symbol Search (processing speed) was also administered. 

Results: Preliminary data analysis from this ongoing study suggests no group differences for accuracy or response time across the three IT tasks (p’s>.05), but the ASD group scored lower on Symbol Search compared to the TD group. Significant positive correlations were found between IQ and some of the measures of IT for the ASD group (p<.05). 

Conclusions: Finding no differences in IT performance supports a previous study showing no IT advantage in high functioning children with ASD. Furthermore, these preliminary data show that manipulations to increase motor demands did not lead to a decrease in accuracy or response time in the ASD group relative to the TD group, indicating that simple motor response time may be intact in our ASD group.  Perhaps the increased complexity of the stimuli in Symbol Search is what interferes with ASD performance, as opposed to its motor demands.