Jacqueline Fagard

Unimanual and bimanual tasks and the assessment of handedness in toddlers

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 (passive\active) 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 right-handedness 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.

Age Changes in Interlimb Coupling and the Development of Bimanual Coordination

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.

Linked proximal and distal changes in the reaching behavior of 5- to 12-month-old human infants grasping objects of different sizes

Abstract This study evaluates age-related proximal and distal changes in reaching organization for objects of different sizes. To this end, eight objects ranging from 2 to 9 cm diam. were presented to 23 infants ages 5 to 12 months. Proximal control was determined by the relative frequencies of bimanual reaching for large and small objects. Distal control was assessed by hand opening and orientation with respect to an object, and by the proportion of the object being included within hand opening at touch. Five-month-old infants tended to reach bimanually regardless of object size. Starting at 7 to 8 months, infants tended to reach for large objects bimanually more often than for small ones. Only at 11 to 12 months did reaching closely reflect the object’s diameter. The frequency of thumb-index finger angle opening during the approach phase also increased after 7 to 8 months of age, as well as the adjustment of the angle to the object diameter and the proportion of the object within hand opening at touch. Proximal and distal changes appeared coupled at 5 to 6 months, when the few subjects showing evidence of some proximal adjustments to object size were also those who exhibited some distal adjustments. After they started to appear, however, proximal and distal adjustments seemed to be independent, as revealed by the lack of correlation of proximal and distal changes between 7 and 12 months.

Cultural influences on the development of lateral preferences: a comparison between French and Tunisian children.

We compared the development of laterality in two cultures that differ in pressure against left‐handedness. Tunisian children, who are discouraged by their parents from using their left hand for all food‐related activities, were compared to French children, who are allowed to use either the left or right hand. The subjects were 5, 7, and 9 years of age. To check the development of laterality, we tested hand preference (for writing and for performing 14 other manual activities), right–left performance difference, eye preference, and foot preference. The results showed that the frequency of left‐handedness and left‐eyedness was lower among Tunisian than among French children; this was particularly clear at age 5. Group difference almost disappeared in primary school children. Footedness did not differ between the two groups. Tunisian right‐hand writers, although they probably included some children who might not have been right‐handed without the cultural pressure, were not less consistent than French right‐hand writers on the 14‐item scale; they even showed a greater performance difference in favour of the right hand than the French on the pegboard task. These results may indicate that cultural pressure influences handedness at an early age, perhaps by leading towards right‐handedness in children whose genetic background might otherwise have induced a chance‐determined pattern of handedness.

Onset of bimanual coordination and symmetry versus asymmetry of movement

Abstract Infants were presented with four objects requiring different kinds of manipulation. Bimanual manipulations which could be performed with symmetrical movements were succeeded earlier than manipulations requiring asymmetrical movements. A right-handed pattern for bimanual coordination (left hand holding/right hand active) was observed as early as bimanual manipulation itself—as of 10 months of age.

Handedness for grasping objects and declarative pointing: A longitudinal study

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 hemispheres 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.

Reaching and grasping a moving object in 6-, 8-, and 10-month-old infants: Laterality and performance

The goal of this study was to investigate some of the visuo-motor factors underlying an infants developing ability to grasp a laterally-moving object. In particular, hand preference, midline crossing, and visual-field asymmetry were investigated by comparing performance as a function of the objects direction of motion. We presented 6-, 8-, and 10-month-old infants with a graspable object, moving in a circular trajectory in the horizontal plane. Six-month-old infants reached for the object with the ipsilateral hand and grasped it with the contralateral hand. Eight-month-old infants showed a strong right-hand bias for both reaching and grasping. Ten-month-old infants showed a greater diversity of strategy use including bimanual and successful ipsilateral grasping following ipsilateral reaching in both directions of motion. Thus, motor constraints due to spatial compatibility, hand preference and bimanual coordination (but not midline crossing) must be taken into account to understand age differences in grasping a moving object.

The effects of reading-writing direction on the asymmetry of space perception and directional tendencies: a comparison between French and Tunisian children.

We compared the influence of reading and writing habits on the asymmetry of space perception and the directional tendencies of French and Tunisian right-handers, aged 5, 7, and 9 years. By comparing two groups of children who use the opposite direction for writing (from left to right for French, from right to left for Arabic), before and after being taught to read in school, we evaluated the impact of writing direction on these asymmetries. A bisection task, a circle-drawing task, and a dot-filling task were used to assess spatial asymmetries and directional tendencies. On the bisection task, a group difference emerged at 9 years, with the French children bisecting the line to the left of the true centre, and the Tunisian children showing no bias. On the circle-drawing task, there was a group difference from 7 years on, as the French children, but not the Tunisian children, used increasing counterclockwise movements. Finally, on the dot-filling task performed with the right hand, the French children filled in significantly more dots when going from left to right from 7 years on, whereas Tunisian children filled in more dots when going from right to left. These results show the impact of basic tendencies in younger children (ipsilateral bias in line bisection, clockwise direction in circle drawing, outward tendency for horizontal displacement in dot filling), as well as the impact of writing direction on spatial asymmetries after learning to read. The results are also discussed in reference to the differences between the two languages, the closeness of the French direction of writing to spontaneous neural-based tendencies, and the influence of learning French at age 8 for the Tunisian children.

Bimanual stereotypes: bimanual coordination in children as a function of movements and relative velocity.

Five-, 7-, and 9-year-old children were trained and tested in a bimanual coordination task that required them to rotate two cranks (either at the same or at different velocities) using mirror (inwards or outwards) or parallel movements (clockwise or counterclockwise). The task consisted of tracing two lines of different slants, by turning the two cranks either at the same velocity (to draw the 45 degrees slanted line) or at different velocities (to draw the 22 degrees line). The same-velocity condition resulted in significantly better performance than the different-velocities condition with the age x angle interaction: the performance in the different-velocities condition improved considerably at 9 years of age. Mirror movement induced faster and more accurate performance relative to parallel movements in the same-velocity condition but not in the different-velocities condition. This difference was much greater in 5- and 7-year-olds than in 9-year-olds. The results are interpreted as reflecting a decreasing influence of motor constraints on bimanual coordination.

Handedness for grasping objects and pointing and the development of language in 14-month-old infants

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.