Reaching with one arm to the other: Coordinating touch, proprioception, and action during infancy.

Reaching to target locations on the body has been studied little despite its importance for adaptive behaviors such as feeding, grooming, and indicating a source of discomfort. This behavior requires multisensory integration given that it involves coordination of touch, proprioception, and sometimes vision as well as action. Here we examined the origins of this skill by investigating how infants begin to localize targets on the body and the motor strategies by which they do so. Infants (7-21 months of age) were prompted to reach to a vibrating target placed at five arm/hand locations (elbow, crook of elbow, forearm, palm, and top of hand) one by one. To manually localize the target, infants needed to reach with one arm to the other. Results suggest that coordination increases with age in the strategies that infants used to localize body targets. Most infants showed bimanual coordination and usually moved the target arm toward the reaching arm to assist reaching. Furthermore, intersensory coordination increased with age. Simultaneous movements of the two arms increased with age, as did coordination between vision and reaching. The results provide new information about the development of multisensory integration during tactile localization and how such integration is linked to action.

A perception--action perspective on tool use development.

In this essay I argue for a new wave of research on tool use development. Advances in the literature on perception-action development hold important clues for how tool use unfolds in children. These advances suggest that tool use may be a more continuous developmental achievement than has been previously believed. On this view, tool use is rooted in the perception-action routines that infants employ to gain information about their environments. Although tools alter the properties of effector systems, children use tools to explore and change their environments, building on efforts that originate in infancy. Based on this approach, new research directions are suggested, including efforts designed to investigate the processes by which children detect and relate affordances between objects, coordinate spatial frames of reference, and incorporate early-appearing action patterns into instrumental behaviors.

The development of detour ability during infancy.

3 longitudinal studies were conducted to examine the generalization of detour ability across motor responses and barrier types and the relationship between the development of object permanence and detour ability. In Experiment 1, 12 8-month-olds were tested every 3 weeks for 4 months on 4 different detour problems and Stage 4 and 6 object permanence tasks. In the detour problems, infants had to reach or move around a transparent or opaque barrier to obtain an object. The results indicated that infants made reaching detours before corresponding locomotor ones and generally made detours around opaque barriers before transparent ones. Infants also solved the Stage 4 task before the detour problems but failed to solve the Stage 6 task before testing ended. The results of Experiments 2 and 3 suggested that the difference in reaching and locomotor detour performance was not an artifact of barrier length or the infant's position relative to the barrier. The overall results are discussed in relation to issues of developmental synchrony and Piaget's theory of infant spatial development.

Developmental biodynamics: brain, body, behavior connections.

This special section, Developmental Biodynamics: Brain, Body, Behavior Connections, celebrates a renewed and revitalized interest in the study of motor development. The renewed interest has been sparked by advances in the neurosciences, biomechanics, and behavioral sciences and, importantly, in the attempts to integrate theories and findings across these disciplines. In this introduction to the special section, we consider the contributions that have led to a reinvigorated field of motor development and to its new interdisciplinary look. We highlight the papers in the special section by discussing how they illustrate related advances across research in the neurosciences, biomechanics, and behavioral sciences and how progress across these domains has come to define and characterize the emerging field of developmental biodynamics.

Using writing instruments: invariances in young children and adults.

In 2 studies, developmental changes in variability associated with handwriting were investigated. In Study 1, variability in grip patterns and pen positioning relative to a flat surface were examined in 3- and 5-year-olds and adults. The results indicated that between 3 and 5 years of age there is a reduction in the number of grips that individual children routinely use and a reduction in variability associated with pen-surface positioning. In Study 2, the 3-year-old children who participated in Study 1 were tested 6 months later. In comparison to young 3-year-old children, older 3-year-olds use an adult grip pattern more often and are less variable in pen-surface positioning, although the use of multiple grip patterns is still common. The findings from both studies are considered in relation to prior research that emphasized modal patterns of motor development and newer work that uses developmental changes in variability to understand the acquisition of motor skill.

The development of anticipatory hand orientation during infancy.

The development of infants' prehensile adjustments regarding the orientation of objects was investigated. Five- and nine-month-olds (N = 16 per group) were presented with horizontally and vertically oriented dowels to determine at what point during the reach, hand orientation approximated that of the dowel. Nine-month-olds rotated their hands appropriately, early in the course of the reach, i.e., before tactual contact of the dowel, whereas five-month-olds did so mostly after tactual contact. Analyses of the effects of trials within the experimental session indicated that this age difference was not associated with practice or fatigue effects. The results are discussed in relation to the development of visual control of prehensile behavior.