Claes von Hofsten

An action perspective on motor development

Motor development has all too often been considered as a set of milestones with little significance for the psychology of the child. Nothing could be more wrong. From an action perspective, motor development is at the heart of development and reflects all its different aspects, including perception, planning and motivation. Recent converging evidence demonstrates that, from birth onwards, children are agents who act on the world. Even in the newborn child, their movements are never just reflexes. On the contrary, they are purposeful goal-directed actions that foresee events in the world. Thus, motor development is not just a question of gaining control over muscles; equally important are questions such as why a particular movement is made, how the movements are planned, and how they anticipate what is going to happen next.

Preparation for grasping an object: A developmental study.

The development of visually controlled grasping actions was studied in two experiments. An optoelectronic technique (SELSPOT) was used to monitor the opening and closing of the hand during reaching actions by measuring the change in the distance between thumb and index finger. The purpose of Experiment 1 was to establish an adult criterion for the development. It was shown that adults started closing the hand around the target well before touch and that the timing was dependent on the size of the target. The hand started to close earlier when grasping a small rather than a large target. In addition, the degree of hand opening was also less for a small than for a large target. In Experiment 2 it was shown that infants who were 5-6, 9, and 13 months of age also controlled their grasping actions visually and started closing the hand around the target in anticipation of the encounter rather than as a reaction to the encounter. However, the strategy of the two younger age groups was different from that of adults. They started closing the hand closer to the time of contact with the target than did the 13-month-olds, who were comparable to adults in this respect. The timing was not dependent on the size of the target in any of the infant groups. In all age groups, reaching and grasping were most commonly organized in a continuous way; that is, the hand started to close without any interruption in the approach. The opening of the hand was found to be adjusted to target size in the 9- and 13-month-olds but not in the 5-6 month olds.

The iCub humanoid robot: An open-systems platform for research in cognitive development

We describe a humanoid robot platform--the iCub--which was designed to support collaborative research in cognitive development through autonomous exploration and social interaction. The motivation for this effort is the conviction that significantly greater impact can be leveraged by adopting an open systems policy for software and hardware development. This creates the need for a robust humanoid robot that offers rich perceptuo-motor capabilities with many degrees of freedom, a cognitive capacity for learning and development, a software architecture that encourages reuse & easy integration, and a support infrastructure that fosters collaboration and sharing of resources. The iCub satisfies all of these needs in the guise of an open-system platform which is freely available and which has attracted a growing community of users and developers. To date, twenty iCubs each comprising approximately 5000 mechanical and electrical parts have been delivered to several research labs in Europe and to one in the USA.

Predictive reaching for moving objects by human infants.

Abstract To what degree do infants use a predictive strategy when reaching for moving objects? This question was studied longitudinally in five infants from 18 to 36 weeks of age. The aiming of 356 reaches were analyzed by a technique that took into consideration the three-dimensional properties of the reaches. Each reach was divided into ballistic steps and the aiming of each step was calculated and compared with an optimal value. It was found that the infants studied had an ability to reach for fast moving objects in a predictive way. Further, the results show that the predictive ability is remarkably good in the lowest age groups which suggests that it is, at least partly, prewired. What develops seems mainly to be the mobility aspects of reaching which makes for more economical and flexible reaching. Older infants reach successfully for the fast moving object also with a nonpredictive chasing strategy.

Development of Visually Guided Hand Orientation in Reaching.

The development of an ability to use vision in adjusting the hand and the fingers to the orientation of an object to be grasped was studied in a group of 15 infants. They were 18 weeks at the first session and were seen at 4-week intervals until 34 weeks old. At each session they were presented with horizontal and vertical rods. The orientation of the hand of the infant when reaching for these rods was measured at each 60-msec interval during the last 540 msec of the approach. It was found that even at the youngest age there were signs of adjustment of the hand to the orientation of the object. However, at that age the adjustments were rather incomplete. During the months that followed there was a rapid improvement in the skill studied. The findings were in accordance with the idea that information about object orientation is accessible to the manual system when infants start reaching for objects but that the system has yet to be tuned and calibrated before functioning adequately.

Catching Skills in Infancy

Infants were induced to reach for fast moving objects whose velocity and starting position varied. Altogether, 144 reaches were analyzed by a technique that took into consideration the three-dimensional properties of reaches. It was found that reaches in all conditions were aimed close to the meeting point with the object. The precision in timing of a reach was about a twentieth of a second, and the systematic timing errors were close to zero. The results suggest that the infant reaches in reference to a coordinate system fixed to the moving object instead of to the static background, that is, the infants hand is moved with the object at the same time as it is moved toward the object. It is concluded that the capacity to time and coordinate ones movements in the catching of a moving object is a very basic and early developed skill. Language: en

Observations on the Development of Reaching for Moving Objects

Abstract How infants come to master reaching for moving objects was studied in a situation where the distance to and the velocity of the moving object varied. Eleven infants participated in the study. They were from 12 to 24 weeks old at the first session, were seen at 3-week intervals until 30 weeks old, and were finally seen once at 36 weeks old. The following behaviors were observed from video recordings: frequency of fixated and followed motions, latency to first goal-directed behavior, type of goal-directed behaviors, and type of reaches. It was found that by the time the infant masters reaching for stationary objects he will also successfully reach for moving ones. Eighteen-week-old infants caught the object as it moved at 30 cm/sec. The results suggest a basic human capacity to time-coordinate ones behavior with external events, and to foresee in ones actions future positions of moving objects.

THE INTEGRATION OF SENSORY INFORMATION IN THE DEVELOPMENT OF PRECISE MANUAL POINTING

The development of manual pointing was studied in 270 children from 4 yr of age to 12 yr of age. Fifteen boys and 15 girls were included in each age group. The task was to place pins underneath a table-top at positions seen or felt on the table-top. Each child was tested in four different conditions: both visual and proprioceptive information about the position of the dot to be pointed at could be provided, just one of these two sources of information could be provided, or none of them. Errors were analysed in terms of systematic and random error. The results show that in all age groups, performance was superior when visual information about the position of the dot was provided. The ability to utilize visual information was found to be rather good already at the youngest ages. In the visual conditions the random error decreased with age in a gradual and linear fashion but the systematic error did not, it decreased and increased and decreased again. Errors were substantially smaller at 7 and 11 yr of age. The ability to use information from the proprioceptors improved remarkably during the youngest ages. All the improvement of the random error between 4 and 5 yr of age could be attributed to this factor. The systematic error in all conditions was found to be displaced towards the contralateral side of the body, but this effect was strongest in the proprioceptive condition. A strong interaction between sex and hand used in pointing was found in the systematic errors but none in the random errors. The interaction could be described as a nondominant hand disadvantage of the girls.

Eye, head and trunk control : The foundation for manual development

Mastery of reaching and manipulation relies on adequate postural control. The trunk must be balanced relative to a base of support to allow free movements of the arms and hands. Moreover, the head must be supported flexibly by the trunk so that gaze can be directed toward the target to provide a spatial frame of reference for reaching. For fine manipulation it is also crucial to avoid retinal slips which would introduce blur. Stabilizing gaze is generally accomplished through adjustments of both eye and head position. Until gaze is stabilized, it is difficult to establish a frame of reference between the target and the self. Thus, a nested hierarchy of support involving the eyes, head, and trunk forms an important foundation for manual activity.

Prospective Control: A Basic Aspect of Action Development

The concept of action is examined, with particular attention to the ontogenetic origin of actions and their developmental course. It is argued that actions constitute dynamic interactions between an o