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Quantifying Repetitive Hand Flapping Kinematics in Autistic and Non-Autistic Toddlers Using Video-Based Pose
Jan Stenum1, Elizabeth Eiler2, Ryan T Roemmich1,3
1Department of Physical Medicine and Rehabilitation, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Developmental Science
|March 26, 2026
Summary
Autistic toddlers showed greater amplitude in repetitive hand flapping compared to non-autistic toddlers, but frequency did not differ. Analyzing individual flapping events, rather than averages, revealed these kinematic differences in early development.
Area of Science:
- Developmental psychology
- Biomechanical analysis
- Artificial intelligence in healthcare
Background:
- Repetitive behaviors like hand flapping are common in autism spectrum disorder (ASD).
- Distinguishing clinically meaningful differences in hand flapping between autistic and non-autistic toddlers before age 2 is challenging.
- Subtle movement variations may be detectable using advanced technology.
Purpose of the Study:
- To investigate kinematic differences in repetitive hand flapping between autistic and non-autistic toddlers.
- To determine if amplitude and frequency of hand flapping differ between groups.
- To explore the utility of computer vision in identifying early behavioral markers.
Main Methods:
- Utilized AlphaPose, an AI-powered computer vision tool, to analyze video recordings of toddlers during a bubble play activity.
- Quantified the amplitude and frequency of repetitive hand flapping from manually annotated video segments.
- Compared kinematic data between 14 toddlers with ASD and 14 without ASD, aged 13-16 months.
Main Results:
- Event-level analysis revealed significantly greater amplitude of hand flapping in autistic toddlers compared to non-autistic toddlers (p = 0.028).
- No significant differences in the frequency of hand flapping were found between groups (p = 0.464).
- Event-averaged analyses masked these amplitude differences, indicating variability in findings based on analytical approach.
Conclusions:
- Event-level analysis of repetitive hand flapping amplitude may offer a more sensitive method for identifying early kinematic differences in toddlers.
- The findings highlight the importance of fine-grained analysis to understand subtle behavioral variations in early development.
- Computer vision techniques show promise for objective assessment of early developmental behaviors.

