Motor Control Adherence to the Two-thirds Power Law Differs in Autistic Development.
Emily Fourie, Szu-Ching Lu, Jonathan Delafield-Butt and 1 others
PMID 38280136WHAT IT FOUND
Autistic children aged 4 to 8 showed steeper velocity changes when drawing curves on an iPad compared to typically developing peers.
They also exhibited higher jerk, indicating less smooth movement. These kinematic differences did not correlate with overall fine motor scores.
Key findings
01During tracing tasks, autistic children had beta values of 0.36 versus 0.33 for typically developing children, suggesting their speed changed more drastically between straight and curved parts of the movement.
02Autistic participants demonstrated significantly greater jerk and acceleration on both drawing and tracing trials compared to the typically developing group, with jerk mean values reaching 9663.98 versus 3996.15 during drawing.
03While typically developing children showed smoother movement as they aged, autistic children showed no significant age-related improvement in kinematic metrics, indicating a lack of developmental progression in this sample.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTsWhat it means for SLPs
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What it does not show
The sample size was small (57 total participants), limiting the generalizability of the findings. The groups differed significantly in IQ, with the TD group having higher verbal and full-scale IQ scores, which could influence task performance. The study was cross-sectional, so it cannot confirm whether the lack of age-related improvement in autistic children represents true developmental stasis or other factors. The iPad task lacked ecological validity, as drawing ellipses is not a common everyday movement. Kinematic metrics did not correlate with the Vineland motor scores, possibly because the parent-report measure has a narrow range or does not capture the specific motor qualities assessed by the iPad task.
Declared interests
The study was funded by the MIND Institute at the University of California, Davis. No other conflicts of interest were reported.
The easy way to misread this
Do not assume that iPad-based kinematic differences directly reflect a child's overall fine motor ability in daily life. The study found no significant association between the tablet task metrics and parent-reported fine motor scores, suggesting these digital measures may capture a specific type of motor control distinct from functional skills.