Haptic grasping configurations in early infancy reveal different developmental profiles for visual guidance of the Reach versus the Grasp.

The Dual Visuomotor Channel theory posits that reaching consists of two movements mediated by separate but interacting visuomotor pathways that project from occipital to parietofrontal cortex. The Reach transports and orients the hand to the target while the Grasp opens and closes the hand for target purchase. Adults rely on foveal vision to synchronize the Reach and the Grasp so that the hand orients, opens, and largely closes by the time it gets to the target. Young infants produce discrete preReach and preGrasp movements, but it is unclear how these movements become synchronized under visual control throughout development. High-speed 3-D video recordings and linear kinematics were used to analyze reaching components, hand orientation, hand aperture, and grasping strategy in infants aged 4-24 months compared with adults who reached with and without vision. Infants aged 4-8 months resembled adults reaching without vision; in that, they delayed both Reach orientation and Grasp closure until after target contact, suggesting that they relied primarily on haptic cues to guide reaching. Infants aged 9-24 months oriented the Reach prior to target contact, but continued to delay the majority of Grasp closure until after target contact, suggesting that they relied on vision for the Reach versus haptics for the Grasp. Changes in sensorimotor control were associated with sequential Reach and Grasp configurations in early infancy versus partially synchronized Reach and Grasp configurations in later infancy. The results argue that (1) haptic inputs likely contribute to the initial development of separate Reach and Grasp pathways in parietofrontal cortex; (2) the Reach and the Grasp are adaptively uncoupled during development, likely to capitalize on different sensory inputs at different developmental stages; and (3) the developmental transition from haptic to visual control is asymmetrical with visual guidance of the Reach preceding that of the Grasp.