Object size as a determinant of grasping in infancy

Area of Science:

• Developmental Psychology
• Motor Control
• Infant Motor Development

Background:

• Prehensile ability is crucial for infant interaction with the environment.
• Understanding the developmental trajectory of grasping is key to identifying motor milestones.

Purpose of the Study:

• To examine the early development and patterns of prehensile ability in infants.
• To investigate how infants adjust their grip configurations based on object size.
• To determine the underlying factors limiting prehension in younger infants.

Main Methods:

• Infants aged 5, 7, and 9 months were presented with objects of varying sizes (0.5 to 14.0 cm).
• Grasp configurations and object-directed reaches were recorded and analyzed.
• The study focused on the use of radial digits (thumb, index, and long finger) in grasping.

Main Results:

• Infants as young as 5 months could differentiate grip configurations based on object size.
• The frequency of grasps using the most radial digits increased significantly with age (10-fold from 5 to 9 months).
• Younger infants primarily directed grasps using radial digits towards smaller objects, suggesting a motor control limitation rather than perceptual or knowledge deficits.

Conclusions:

• The development of prehension is influenced by the maturation of cortico-motoneural connections, which improve with age.
• The findings challenge traditional views of a rigid, sequential development of infant prehension.
• Differences in object size and presentation methods may explain discrepancies with previous research.