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Published on: April 16, 2014
The transition to reaching: mapping intention and intrinsic dynamics
1Department of Psychology, Indiana University, Bloomington 47405.
Insights
Infant reaching emerges when babies intentionally adjust arm force and compliance, adapting to tasks. This skill arises from natural movement dynamics rather than pre-programmed motor patterns.
Area of Science:
- Developmental neuroscience
- Motor control
- Infant behavior
Background:
- Directed reaching is a key developmental milestone.
- Understanding the emergence of intentional movement is crucial.
Purpose of the Study:
- Investigate how intentional reaching develops from intrinsic infant movement dynamics.
- Examine how infants adapt their initial reaches to task demands.
Main Methods:
- Weekly observation of 4 infants performing a standard reaching task.
- Identification of the onset of arm-extended reaches.
- Analysis of movement strategies before and after reach onset.
Main Results:
- Infants first reached between 12 and 22 weeks of age.
- Infants modulated movement force and energy based on their baseline dynamics.
- Reaching strategies were adapted to the task in subsequent weeks.
Conclusions:
- Reaching emerges through intentional adjustments in arm force and compliance, often involving muscle coactivation.
- Motor patterns are a consequence of system dynamics and active exploration, not pre-programmed trajectories.
Abstract:
The onset of directed reaching demarks the emergence of a qualitatively new skill. In this study we asked how intentional reaching arises from infants' ongoing, intrinsic movement dynamics, and how first reaches become successively adapted to the task. We observed 4 infants weekly in a standard reaching task and identified the week of first arm-extended reach, and the 2 weeks before and after onset. The infants first reached at ages ranging from 12 to 22 weeks, and they used different strategies to get the toy. 2 infants, whose spontaneous movements were large and vigorous, damped down their fast, forceful movements. The 2 quieter infants generated faster and more energetic movements to lift their arms. The infants modulated reaches in task-appropriate ways in the weeks following onset. Reaching emerges when infants can intentionally adjust the force and compliance of the arm, often using muscle coactivation. These results suggest that the infant central nervous system does not contain programs that detail hand trajectory, joint coordination, and muscle activation patterns. Rather, these patterns are the consequences of the natural dynamics of the system and the active exploration of the match between those dynamics and the task.
