The goal of this study was to examine the relations between three different measures of handedness: unimanual reaching, bimanual manipulation and unimanual manipulation. The appropriateness of the task chosen to evaluate handedness was also explored by contrasting different bimanual manipulation tasks for the more or less differentiated (passiveaactive) roles assigned to each hand. Forty children, between 18 and 36 months of age, were tested in the three conditions. The results show that the degree of bimanual handedness is greater on the bimanual tasks with a strong role differentiation than on the tasks with less differentiation. Bimanual tasks with a strong role differentiation elicited more righthandedness than unimanual reaching. Among the children who showed handedness in reaching, the correlation between unimanual and bimanual handedness was high, especially for right-handers. For some tasks, bimanual handedness appeared at the earliest age studied here (18 months), and there was little relationship between bimanual handedness and bimanual skill. In contrast with unimanual reaching, there was no age-related change in the degree of handedness for either bimanual or unimanual manipulation. There was a bias toward the use of the right hand for unimanual manipulation. It was concluded that grasping is not the best task to employ to look for robust evidence of handedness, and that bimanual tasks offer a better way to estimate handedness in children, as long as the tasks are carefully chosen.

The goal of this study was to evaluate the relationship between object-related handedness and handedness for communicative gestures. We observed 22 infants aged 14 months on a baby laterality test consisting of grasping objects in different conditions, on a pointing task with targets placed out of reach at different spatial positions from left to right, and on word understanding and word production. Results show that 77% of infants pointed to the left, middle, and right targets. The majority of infants were right-handed for pointing--except for the far left target--and, to a lesser extent, for grasping objects, but there was no significant relation between the two measures of handedness. The frequency of pointing tended to be related to the number of words understood, and infants right-handed for pointing understood and produced significantly more words than non-right-handed pointers. These results are interpreted as confirming the link between pointing and language development, and as showing that communicative gesture lateralisation is not a mere consequence of object-related handedness, at least during development. Whether lateralised communicative gesture reinforces a pre-existing tendency to use the right hand to interact with objects remains an open question.

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It is still unclear whether infants become right-handed because of their left-hemisphere specialization for language (through gestural communication for instance), whether they speak predominantly with their left hemisphere because of this hemisphere's superiority in controlling sequential actions which first results in right-handedness, or whether the two lateralization processes develop independently. To tackle this question, we followed 26 human infants from 8 to 20 months to evaluate the temporal relationship between the emergence of hand preference for grasping objects and for declarative pointing (communicative gesture). Our results show that when grasping and pointing are compared in similar conditions, with objects presented in several spatial positions, the tendency to use the right hand is significantly larger for pointing than for grasping, and both hand preferences are loosely correlated. This suggests that, at least at the age studied here, hand preferences for grasping and for declarative pointing develop relatively independently.

The ability to sense and use the body parts in an organized and differentiated manner is a precursor of body knowledge in infancy. To acquire this ability, the infant's brain might explore the perceptual consequences of its bodily actions. Undifferentiated body movements would gradually be replaced by more precise actions. Only a very few studies have tested this ‘global‐to‐local’ hypothesis, and none of them have so far been replicated. In this study, we assessed arm differentiation in 4‐, 6‐, and 8‐month‐old infants using a new contingency detection task in which infants have to detect a contingency between one of their arms’ activity and an audiovisual stimulus on a screen. We found that 4‐ to 8‐month‐old infants seem to be able to use their arms in a differentiated manner. However, surprisingly, we were not able to show a developmental trend in arm differentiation between 4 and 8 months of age. What is already known on this subject? Foetuses and infants possess coarse control of their body and may be sensitive to sensory feedback caused by their own movements. Body knowledge might develop during the first year of life in what can be called a ‘global‐to‐local’ manner. Nevertheless, the precise age at which infants come to possess well‐differentiated local body knowledge requires further investigation. What the present study adds? 4‐ to 8‐month‐old infants seem able to use their arms in a differentiated manner when exposed to an audiovisual stimulation contingent on movements of one of their arms. However, we found no developmental trend in arm differentiation between 4 and 8 months of age. We hypothesize that infants' sensitivity to sensorimotor contingencies and their ability to narrow down contingencies to a specific limb might evolve with age as a function of the infant's current sensorimotor interests.

Changes in interlimb coupling, and their role in the development of bimanual coordination, were studied longitudinally in 6- to 12-month-old infants (N = 6). Infants were observed while they were reaching for simple objects of 2 different sizes. Their use of a uni- versus bimanual strategy for reaching as well as the coupling of their bimanual movements were compared; progress in bimanual coordination of complementary movements was evaluated on 3 different bimanual tasks. The bimanual tasks involved an asymmetrical cooperation between the 2 hands. Although spatiotemporal coupling of bimanual reaching movements did not decrease during the age period studied, infants around 7 months of age used their 2 hands infrequently for reaching. Occurrences of bimanual reaching were particularly low at the session preceding the first bimanual success at a bimanual task. This suggests that the temporal coincidence between greater independence of the 2 hands and progress in bimanual coordination of complementary movements acts in 2 directions: Infants may be more at ease when using their 2 hands in differentiated patterns as the hands move less in synchrony, but, in turn, they may be less likely to move their hands in synchrony as they anticipate mirror manipulations of the object less. The frequency of bimanual reaching increased toward the end of the 1st year. This might have been caused by an increase in the repertoire of bimanual asymmetrical object manipulations and by the fact that the development of bimanual coordination allows infants to manipulate objects with complementary movements even after a bimanual approach toward the object.