Early manifestations of manual specialisation in infants: a longitudinal study from 20 to 30 weeks.

This longitudinal study examined lateral differences between latency time of the two hands during the development of prehension in 12 infants from 20 to 30 weeks. Latency time (LT) is defined as the delay between the visual localisation of a reachable target and the beginning of the movement and could be considered as a phase in the preparation of action. If LT varies with the hand used and the type of movement, this would suggest differences in information processing (nature and/or quantity). Results show that the latency time is shorter for the left hand approach movements and shorter for the right hand grasping movements. These findings are in favour of a manual specialisation--clearly present from 20 weeks--and are discussed in a possible hemispheric specialisation perspective.