This study examines the acquisition of internal stability as it relates to the development of prehension in normal infants. Thirty-two subjects, 7 to 14 months of age, were observed grasping Cheerios from styrene surfaces that provided different amounts of support to the infants’ hands. The subjects were scored on the grasp patterns they used and on their success in securing a Cheerio without dislodging the styrene surface from a platform. Success increased with age, thus demonstrating a developmental progression in the acquisition of upper extremity internal stability. Consistency of grasp also increased with age. Whereas the youngest infants (7 to 8 months old) reverted to immature grasp patterns on the less stable surfaces, the oldest infants (13 to 14 months old) used mature pincer grasp patterns consistently. Infants 10 to 11 months old seemed to be in a transitional stage between the variability of grasp seen in the youngest infants and the consistency achieved by the oldest group.

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