Frontiers in Psychology (Jan 2015)

Independent development of the Reach and the Grasp in spontaneous self-touching by human infants in the first six months

  • Brittany L Thomas,
  • Jenni Marie Karl,
  • Ian Q Whishaw

DOI
https://doi.org/10.3389/fpsyg.2014.01526
Journal volume & issue
Vol. 5

Abstract

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The Dual Visuomotor Channel Theory proposes that visually guided reaching is a composite of two movements, a Reach that advances the hand to contact the target and a Grasp that shapes the digits for target purchase. The theory is supported by biometric analyses of adult reaching, evolutionary contrasts, and differential developmental patterns for the Reach and the Grasp in visually guided reaching in human infants. The present ethological study asked whether there is evidence for a dissociated development for the Reach and the Grasp in nonvisual hand use in very early infancy. The study documents a rich array of spontaneous self-touching behavior in infants during the first six months of life and subjects the movements to analyses of body target, contact type, and Grasp. Video recordings were made of resting alert infants biweekly from birth to 6 months. In younger infants, self-touching targets included the head and trunk. As infants aged, targets became more caudal including the hips, legs, and feet. In younger infants hand contact was mainly made with the dorsum of the hand, but as infants aged contacts included palmar and eventually grasp and manipulatory contacts with the body and clothes. The relative incidence of caudal contacts and palmar contacts increased concurrently and were significantly correlated throughout the period of study. In contrast, developmental increases in self grasping emerged a few weeks after the increases observed in caudal and palmar contacts. The behavioral and temporal pattern of these spontaneous self-touching movements suggest that the Reach, in which the hand extends to make a palmar self-contact, and the Grasp, in which the digits close and make manipulatory movements, have partially independent developmental profiles. The results additionally suggest that self-touching behavior is an important developmental phase that allows for the coordination of the Reach and the Grasp prior to their use under visual guidance.

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