Can Autism and Asperger Syndrome Be Distinguished According to Motor Abilities and Perceptual Processing Speed?

Background:  On the autistic spectrum, autism and Asperger syndrome are distinguished with respect to early speech abilities. Speech onset delays and/or certain speech atypicalities are specific to autistics and distinguish them from Asperger individuals. Other reported demarcating features are perceptual and motor skills, with autistics displaying visuo-perceptual peaks and Asperger displaying motor clumsiness.

Objectives:  To investigate whether autistic spectrum individuals stratified on the basis of speech development atypicalities also differ on perceptual and motor variables.

Methods:  30 typically developing, 18 autistic and 17 Asperger (based on clinical diagnosis and speech abilities) participants were assessed with a) an intelligence battery including the Wechsler’s scale of intelligence and the Raven Progressive Matrices b) a motor battery including the Purdue Pegboard and the Annett Peg Moving tests that measure gross and fine motor skills, dexterity, bi-manual and hand-eye coordination; and c) a task measuring perceptual processing speed (PPS), the computerized Inspection Time task. The groups were matched on age (14-27 years), gender and IQ (range 78-129).

Results:  As predicted, the Asperger group did not show any atypicalities in PPS compared to the TD group, while the autistic group was significantly faster than the TD group (p = .028). In the autism group, PPS was correlated with Raven’s Progressive Matrices performance (r=-.80, p<.001) but not in the Asperger group (r=-.34, p=.178). In motor abilities, both Asperger and autistic groups were significantly slower than the typical group at the Annett task with the dominant hand but only the autistic group was significantly slower with the non-dominant hand. Autistic and Asperger groups were also slower than their typically developing controls with either hand at the Purdue Pegboard task. Although there was a trend with Asperger individuals being more impaired than autistics for most subtests of the Purdue, the difference between autistic and Asperger groups was non-significant. 

Conclusions: The results suggest that a faster PPS is specific to the autistic spectrum subgroup with speech onset delays and/or atypicalities while the subgroup without speech atypicalities displayed typical PPS. PPS could thus play a role in enhanced perception in autistics, and contribute to their strong performance on Raven’s Progressive Matrices. Motor abilities did not seem to differ significantly between autistic and Asperger individuals. Although this might be due to a lack of power in the study, it is also possible that this variable cannot distinguish the subgroups, or the tasks used were not measuring the area in which the groups can be differentiated. Appropriate tasks might be ones involving the whole body (ex: balance and whole body coordination) rather than just manual dexterity and coordination.