Handwriting Isochrony in Autistic and Non-Autistic Children

Handwriting difficulties are frequently reported in autistic children and may interfere with academic performance. However, whether fundamental motor principles such as isochrony are preserved in autism remains largely unexplored. To address this question, fifty-five autistic and fifty-nine age-matched non-autistic children (6–12 years), all with intellectual functioning within the normal range, traced the letter “e” at five different sizes on a graphic tablet. Kinematic data were analyzed using the power law MT = T₀ × A γ , where MT is movement time, A the amplitude of “e”, T₀ the baseline time and γ the degree of isochrony. Because reliable estimation of isochrony parameters requires an adequately expressed amplitude-duration relationship, only participants whose data adequately fitted the power law (R² > 0.36) were retained for parameter analyses. In total, twenty-four autistic and thirty-six non-autistic children met this criterion. Frequentist and Bayesian analyses revealed no group differences in the degree of isochrony (γ = 0.45) or baseline time (T₀ = 1.66 s), indicating comparable temporal scaling of handwriting movements from age six among autistic and non-autistic children with a reliable amplitude-duration relationship. Present findings suggest that isochrony control can be preserved in a subgroup of autistic children whose data adequately fit the power-law model. Handwriting difficulties in autism are not necessarily attributable to impaired fundamental motor timing mechanisms and may involve other processes.