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Updated: Jan 6, 2026
Frame-by-Frame Video Analysis of Idiosyncratic Reach-to-Grasp Movements in Humans
Published on: January 15, 2018
Increasing task precision demands reveals that the reach and grasp remain subject to different perception-action
Jenni M Karl1, Braydon M Slack1, Alexis M Wilson1
1Department of Psychology, Thompson Rivers University, Kamloops, BC, Canada.
Insights
Infant reaching and grasping skills are not fully integrated by 12 months. Increased precision demands improved pincer grip formation but impaired reach accuracy in infants.
Area of Science:
- Developmental Psychology
- Motor Control
- Infant Motor Development
Background:
- Infant reach and grasp development are typically considered nearly adult-like by 12 months.
- However, the integration and independent refinement of these skills require further investigation.
Purpose of the Study:
- To examine how increased precision demands affect infant reach and grasp movements.
- To determine if reach and grasp are influenced complementarily or differentially by task precision.
Main Methods:
- Frame-by-frame video analysis of 12-month-old infants' reach and grasp.
- Comparison of movements towards small targets on a narrow pedestal versus a flat table.
Main Results:
- Increased precision demands impaired reach accuracy (directing digits to the target).
- Index-thumb pincer grip formation was facilitated, with more suboptimal contacts transitioning to successful grips.
- Differential effects on reach and grasp suggest incomplete integration.
Conclusions:
- Reach and grasp are not fully integrated by 12 months of age.
- Infant motor control remains sensitive to perception-action constraints under high precision demands.
- Task precision influences reach and grasp independently, highlighting distinct developmental trajectories.
Abstract:
The reach and grasp follow different developmental trajectories, but are often considered to have achieved nearly adult-like precision and integration by 12 months of age. This study used frame-by-frame video analysis to investigate whether increasing precision demands, by placing small reaching targets on a narrow pedestal rather than on a flat table, would influence the reach and grasp movements of 12-month-old infants in a complementary or differential fashion. The results reveal that placing the target atop a pedestal impaired the infants's ability to direct an appropriate digit towards the small target, but did not produce a corresponding decrease in the frequency with which they used an index-thumb pincer grip to grasp the target. This was due to the fact that, although infants were more likely to contact the target with a suboptimal part of the hand in the pedestal condition, a greater proportion of these suboptimal contacts ultimately transitioned to a successful index-thumb pincer grip. Thus, increasing task precision demands impaired reach accuracy, but facilitated index-thumb grip formation, in 12-month-old infants. The differential response of the reach and grasp to the increased precision demands of the pedestal condition suggests that the two movements are not fully integrated and, when precision demands are great, remain sensitive to different perception-action constraints in 12-month-old infants.
