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Lifting weights in neonates: developing visual control of reaching
A L van der Meer1, F R van der Weel, D N Lee
1Idrettsvitenskapelig Institutt, Norwegian University of Science and Technology, Trondheim, Norway.
Insights
Newborn babies use visual feedback to control arm movements and compensate for external forces. This suggests their spontaneous arm-waving is purposeful, not just reflexive.
Area of Science:
- Developmental Psychology
- Neuroscience
- Motor Control
Background:
- Neonatal limb movements are often considered reflexive or purposeless.
- Limited understanding exists regarding early visual-motor integration in newborns.
Purpose of the Study:
- To investigate if newborns adjust arm movements based on external forces.
- To determine the role of visual feedback in neonatal motor control.
Main Methods:
- Measuring spontaneous arm movements in infants under varying conditions of external weight.
- Utilizing visual occlusion and video monitoring to assess the impact of sight on compensatory movements.
Main Results:
- Newborns applied compensatory forces to stabilize the visually perceived hand against external weights.
- Visual occlusion led to a loss of compensatory movement.
- Viewing the contralateral arm via video monitor enabled compensation for weights.
Conclusions:
- Neonatal arm movements are not solely reflexive but demonstrate purposeful, visually guided control.
- These findings challenge traditional views of spontaneous neonatal movements.
- Newborns appear to be developing visual control for reaching behaviors early in life.
Abstract:
To test whether newborn babies take account of external forces in moving their limbs, spontaneous arm-waving movements were measured while the baby lay supine with its head turned to one side. Free-hanging weights, attached to each wrist by strings passing over pulleys, pulled on the arms in the direction of the toes. The results showed the babies applied compensatory forces to keep the hand they faced moving in the same region. In contrast, the (invisible) contra-lateral hand was pulled down by the weights. In a second experiment, where the arms were occluded, both arms were pulled down, suggesting that sight of the arm was necessary in compensating for the weight. In a third, conclusive experiment the babies viewed the arm they were not facing on a small video-monitor and this time the babies kept the visible contra-lateral hand up despite the weights. The results challenge the general view that spontaneous arm movements of neonates are purposeless and either reflexive or due to spontaneous patterned efference to the muscles. Instead, the findings suggest that in waving their arms, neonates are developing visual control of reaching.
