Observations on the Development of Visually-Directed Reaching

Abstract

This paper reports the results of a normative study of the development of visually-directed prehension during the first six months of life. Thirty-four normal infants born and reared under relatively uniform conditions in a state hospital were studied. The technique combined detailed longitudinal observations with a standardized testing procedure designed to elicit visual-motor responses including prehension. A sequence of development is described, categorized into eight stages of two weeks each. A number of separate and distinct visualmotor and tactual motor behaviors were found to contribute to this sequence, culminating in the development of visually-directed reaching just prior to 5 months of age. The prehensory abilities of man and other primates have long been regarded as one of the most significant evolutionary developments peculiar to this vertebrate group (2, 17). In man, the development of prehension is linked phylogenetically with the assumption of erect posture (thus freeing the forelimbs from the service of locomotion), the highly refined development of binocular vision, and the possession of an opposable thumb, among other specializations. One important accompaniment of the development of prehension is man's unique capacity to make and utilize tools. Considering the acknowledged importance of these developments in phylogeny, it is surprising how little is presently known about the ontogeny of prehension in