Background: Sensorimotor issues are common in autism spectrum disorder (ASD), related to core symptoms, and predictive of worse functional outcomes. Deficits in rapid, feedforward processes executed prior to availability of sensory feedback, and continuous, feedback-guided motor behaviors each have been reported, but the degree to which these deficits are distinct or co-segregate in individuals is not well understood.
Methods: To characterize feedforward and feedback control of motor behavior in ASD, we examined saccadic eye movements (feedforward) and sustained precision gripping (feedback) in 109 individuals with ASD and 101 age-matched typically developing (TD) controls (range: 5-28 years). We measured latency and gain of saccades and error, variability, and regularity of precision grip. Linear mixed effects models were conducted to examine whether sensorimotor behavior varied according to diagnostic group, age, handedness, and sex.
Results: Individuals with ASD showed reduced accuracy of saccadic eye movements relative to controls, and their dysmetria was more severe at older ages. Individuals with ASD showed increased precision grip force variability relative to controls, especially at younger ages, while increased motor regularity was more pronounced in older individuals with ASD. Feedforward and feedback motor behaviors were strongly inter-related among controls, but not among individuals with ASD. Saccade dysmetria and increased force variability were associated with ASD symptom severity.
Limitations: Our age-related findings rely on cross-sectional data. Longitudinal studies of component motor skills and their associations with clinical outcomes are needed to clarify neurodevelopmental mechanisms of core and associated symptoms of ASD. Feedforward behavior was characterized in the oculomotor system using ballistic movements completed too rapidly to be guided by online feedback; however, future studies are needed to examine feedforward and feedback processes across both manual and oculomotor systems.
Conclusions: These findings suggest that separate neurodevelopmental mechanisms contribute to feedforward and feedback motor deficits in ASD, and that they are more manifest at different stages in life span development. Our results highlight the needs for more fine-grained approaches to parse separate motor impairments that often are considered as a unitary deficit in ASD, and to characterize variation in motor behaviors across development.