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Updated: Aug 8, 2026
The Structure of Skilled Forelimb Reaching in the Rat: A Movement Rating Scale
Published on: August 8, 2008
Structuring of early reaching movements: a longitudinal study
1Department of Psychology, Umeå University, S-90187 Umeå, Sweden.
Insights
Infant reaching movements become more systematic and adult-like between 19 and 31 weeks of age. Trajectories become straighter, with a dominant transport unit initiating the movement and fewer action units overall.
Area of Science:
- Developmental psychology
- Motor control
- Infant development
Background:
- Understanding the developmental trajectory of reaching is crucial for assessing motor milestones.
- Previous research has identified distinct action units within reaching movements.
Purpose of the Study:
- To quantitatively analyze the changes in reaching movement structure in infants from 19 to 31 weeks of age.
- To investigate the developmental progression towards adult-like reaching patterns.
Main Methods:
- Quantitative analysis of reaching movements in 5 infants.
- Data collection occurred at 19 weeks and every third week until 31 weeks of age.
- Focus on action units, transport units, and trajectory characteristics.
Main Results:
- Reaching movements are consistently structured into acceleration and deceleration phases.
- A dominant transport unit, initiating the reach, becomes more systematic with age.
- The duration of the transport unit increases, and the number of action units decreases, approaching adult patterns.
- Reaching trajectories become progressively straighter with age.
Conclusions:
- Infant reaching undergoes significant developmental changes between 19 and 31 weeks.
- The developing reaching pattern shows a clear trend towards the more efficient, two-phase adult structure.
- These findings provide insights into the maturation of motor control systems in early development.
Abstract:
Reaches, performed by 5 infants, recorded at 19 weeks of age and every third week thereafter until 31 weeks of age, were studied quantitatively. Earlier findings about action units were confirmed. At all ages studied, movements were structured into phases of acceleration and deceleration. Reaching trajectories were found to be relatively straight within these units and to change direction between them. It was also found that at all ages, there was generally one dominating transport unit in each reach. The structuring of reaching movements changed in four important ways during the period studied. First, the sequential structuring became more systematic with age, with the dominating transport unit beginning the movement. Second, the duration of the transport unit became longer and covered a larger proportion of the approach. Third, the number of action units decreased with age, approaching the two-phase structure of adult reaching. Finally, reaching trajectories became straighter with age.
