Visuomotor Skill, Simple Reaction Time and Perceptual Processing Speed in Autism

Background: Although atypicalities in visuomotor coordination, often generically labelled as “clumsiness”, are commonly observed to varying degrees in autistics of all ages, their precise mechanism is poorly understood. The failure to achieve desired spatial and temporal accuracy in a relatively simple task like visually-guided reaching could arise from a range of sources, including visual analysis of target or hand position, hand/body/target coordinate transformation determination, or movement execution.  In addition, while it has been suggested that the Asperger subgroup is particularly likely to exhibit atypical motor behavior, the empirical evidence supporting this assertion has been somewhat inconsistent.

Objectives: To localize the potential sources of atypical visuomotor coordination, we undertook a behavioral analysis of the processes responsible for visually-guided reaching by investigating perceptual analysis, peg moving and simple response generation skills in autistic and Asperger participants.

Methods: We measured perceptual inspection time, peg moving skill and simple manual reaction time in 24 autistic, 22 Asperger and 30 typical participants matched on Wechsler IQ (FSIQ mean=103.20), matrix reasoning skill (Raven Progressive Matrices percentile score mean=69.86,) and age (mean=21.88, range: 14-37). Clinical participants were diagnosed using DSM-IV, ADI-R and ADOS-G standards and none of the subjects were taking medication.  Tasks included: (1) Inspection Time (IT), in which two vertical lines of different length were presented for durations of 10-200 ms and then immediately masked by two irregular lines, participants indicated the longer of the two lines, and stimulus duration was adaptively varied in a staircase psychophysical procedure, (2) Purdue Pegboard (PP), which measures finger dexterity and hand-eye coordination while putting small pegs into a pegboard using left, right, or both hands, (3) Annett Peg Moving (APM), which measures the speed at which larger pegs can be moved from one set of holes to another, and (4) visually-triggered simple reaction time (SRT). Manual preference was controlled by classifying responses as dominant (DH) or nondominant hand (NDH).

Results: The Asperger and autistic groups did not differ from typicals on the IT task (p>0.05) or the visually-triggered SRT task (p>0.05). The Asperger, but not the autistic, group was slower on the PP task (DH: p=0.007; NDH: p=0.023), but not in the bimanual conditions. On the Annett test, the Asperger and autistic groups had longer completion times than controls (Asperger - DH: p=0.015;   NDH: p=0.023 and autistic - DH: p=0.038; NDH: 0.047). Secondary analyses did not identify differences between the Asperger and autistic groups on any of the motor tasks.

Conclusions: We found that both autistic and Asperger participants had atypical performance on two different visuomotor tasks. These differences could not be explained with reference to impairments in either perceptual processing speed or response execution assessed with a simple task. This pattern of findings suggests that the differences observed in the visually-guided reaching tasks cannot be explained by slower sensory information processing or impaired motor execution, but may rather reflect difficulties in integrating dynamically changing sensory guidance information with evolving action plans.