Hemispheric asymmetry and interhemispheric transfer in pointing depend on the spatial components of the movement.

The purpose of the present study was to compare the asymmetry and transfer in 3 pointing movements with increasing spatial requirements. The triggering signal was one of four visual targets appearing on the right or left of a central fixation point (FP). The first task consisted in simply removing the arm from the starting platform; the second was a pointing movement towards the FP, and the third was a classical pointing task towards one of the four lateral targets. 20 right-handers (Rhrs) and 20 left-handers (Lhrs) participated in this experiment. In the classical pointing task (task 3), the reaction times were shorter in the Rhrs using their left hand. No such hand-related difference was observed in the Lhrs. No hand asymmetry was observed in the other tasks. In addition, the responses were faster in the uncrossed than in the crossed conditions, in task 3 only. It was concluded that in pointing tasks, both the hemispheric asymmetry and the interhemispheric transfer depend on the spatial requirements of the movement.

Hemispheric asymmetry and interhemispheric transfer in reaching programming.

The purpose of this study was to explore the intrahemispheric processes and the interhemispheric transfer that occur during the programming of a pointing movement. Twenty five subjects participated in this experiment: 12 were right-handed (Rhr), 12 left-handed (Lhr), and 1 was left-handed with a posterior callosal lesion. The task consisted in producing an open loop pointing response toward a visual target appearing briefly on the right or the left of a central fixation point. Reaction times (RTs) were shorter for the Rhrs when reaching with the left hand than with the right hand. No such hand-related difference was observed in the Lhrs. The left hand advantage indicates that one process was faster in the right hemisphere of Rhrs. This faster process appears not to be visual but motor or visuomotor. For either hand, responses were faster when the target appeared in the visual field homolateral to the pointing hand (uncrossed condition) than when it appeared contralaterally to the hand (crossed condition). The crossed vs uncrossed difference did not vary between Rhrs and Lhrs or between the hands. The transfer time between the hemispheres was symmetrical whatever its direction. The partially callosotomized left-handed subject was two-fold slower than the control Lhrs. His uncrossed responses were faster than the crossed ones, but his interhemispheric transfer time was very asymmetrical: it was normal from right to left hemisphere but was highly increased in the opposite direction. An attempt at modelling the RT data is proposed and the possibility of different callosal locations for the interhemispheric transfer is discussed.

What does the haptic modality do during cognitive activities on letter shapes? A study with left- and right-handers.

This study was undertaken to analyze intermanual (interhemispheric) transfer in left and right handed subject and to assess how information was extracted during finger scanning of letter shape at the different levels of letter processing: shape recognition during a physical matching task, letter recognition in a verbal "meaning" matching task and letter naming. The dichhaptic procedure was used to study interhemispheric relations. It was hypothesized that cognitive activities have a feed-forward effect on the exploration of shapes, and that the performance is related to the nature of the task and to handedness. The exploratory strategies of the two types of handedness were also analyzed. The results showed that response latencies were generally similar for left- and right-handed subjects, but accuracy was better for left than right handers in "verbal" matching with the same overall exploratory strategies. In physical matching, left- and right-handed subjects performed equally but used different exploratory strategies. The naming task was very difficult for both groups but failed to discriminate their on accuracy, response latency, and exploratory strategy. The results are discussed with reference to the different exploratory strategies used and the interhemispheric interaction at work in different cognitive processes.

Letters as spatial-oriented shapes and/or graphemic signs: a developmental study of left- and right-handed girls during the period of learning to read.

This study is concerned with the problem of hemispheric specialization and/or cooperation in relation to development and manual laterality. The processing of alphabetic signs and its relationship to interhemispheric transfer and functional hemispheric asymmetries were studied by comparing left- and right-handed girls during acquisition of reading. The children perform matching tasks with letters having different orientations and with meaningless forms having the same orientations as the letters. Each subject performed the matching under three conditions: right/left intermanual transfer, left/right intermanual transfer, and dichaptic exploration. Results indicate: (1) A differentiated development between the two handednesses. (2) The functional lateralization change was different for left- and right-handed girls, a greater effect of the ability to identify the letter on matching tasks was observed for the right-handed children than for the left-handed children. These last results are discussed with regard to inter-hemispheric transfer and functional hemispheric asymmetry changes. We hypothesized a strategy difference between left- and right-handed girls and a difference in their ability to change their cognitive strategy (left-handers continue to favor a spatial coding with letters).

Some data concerning a sensorimotor versus semiotic processing in a form-recognition task.

This study investigated how sensorimotor activities interact with the geometric characteristics and the meaning of an object during development of writing. These changes were studied in 4- to 7-yr.-old girls. Analysis showed that visuo-spatial activities play a role in denomination and graphic activities, especially during critical periods of development. These activities have varying effects at different stages of development. The spatial factors studied here act differently in a verbal task (denomination) and in a perceptual-motor activity (graphic activity).