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Quantitative assessment of right and left reaching movements in infants: a longitudinal study from 6 to 36 months
Louise Rönnqvist1, Erik Domellöf
1Department of Psychology, Umeå University, SE-901 87 Umeå, Sweden. louise.ronnqvist@psy.umu.se
Insights
Infant reaching kinematics show early right-side preference, suggesting arm laterality precedes hand preference in human handedness development. This pattern was observed consistently across ages, though preterm infants displayed more variability.
Area of Science:
- Developmental Psychology
- Motor Control
- Human Kinematics
Background:
- Human handedness, a complex trait, emerges during early development.
- Understanding the origins of handedness is crucial for developmental neuroscience.
- Previous research has focused on hand preference, but early kinematic patterns are less understood.
Purpose of the Study:
- To investigate the emergence and developmental trajectory of laterality in infant reaching movements.
- To examine the relationship between reaching kinematics and hand preference.
- To compare reaching patterns in preterm versus full-term infants.
Main Methods:
- Longitudinal study tracking 17 infants from 6 to 36 months.
- 3-D kinematic and 2-D video analysis of right-left reaching movements.
- Hand preference assessment at 36 months; comparison with preterm infants.
Main Results:
- Infants showed consistent right-sided reaching kinematics (fewer movement units, straighter paths) from an early age.
- Hand preference was inconsistent in early stages, but kinematic asymmetry was present.
- Preterm infants exhibited more variable and less side-consistent reaching patterns.
Conclusions:
- Human handedness may originate from an early arm preference rather than hand preference.
- Asymmetry in bilateral arm movement projections may precede contralateral hand movement projections.
- Kinematic analysis provides insights into the developmental origins of motor laterality.
Abstract:
This longitudinal study aimed to explore the early presence and developmental pattern of laterality in reaching kinematics and its relationship to side use. In order to do so, 3-D kinematic measurements as well as 2-D video recordings of right-left reaching movements were successively carried out for 17 infants at the ages of 6, 9, 12, and 36 months. Additional investigations of hand preference were made at 36 months. As four infants were prematurely born, their outcomes were compared to those of the fullterm participants. While most of the infants in the early ages showed a rather inconsistent preference in terms of frequency and distributions of right-left side use, the analyses of reaching kinematics revealed a more consistent pattern of fewer movements units (MUs) and straighter right-sided reaching for the majority of infants at all tested ages. However, reaching kinematics from the preterm infants were generally more variable and less side consistent. It is proposed that the development of human handedness originates from an early right arm rather than hand preference in that representations of asymmetry in bilateral projections (involved in arm movements) developmentally precede contralateral projections (involved in refined hand/finger movements).
