Motor control times and strategies in left- and right-handed participants: Behavioral evidence for the hemispheric distribution of motor planning

Background: There is conflicting evidence in favor of the hemispheric distribution of motor planning. Some studies supported the left-hemisphere-dominance hypothesis for motor planning and claimed that the left-hemisphere has a crucial function in motor control even in left-handers. The present study aimed to compare the right- and left-handed participants on motor planning ability and to investigate the performance of their dominant hands in a specific action selection task. Also, the effect of task complexity was assessed. Methods: Twenty right-handers and 20 left-handers performed an action selection task. The participants had to grasp a hexagonal knob with their dominant hand and consequently rotated it 60° or 180 ° clockwise or counterclockwise. Depending on our objects, we used mixed factorial ANOVA and the groups were examined in terms of the planning time, grasping time, releasing time and planning pattern for initial grip selection. The SPSS 19 was used for analyzing the data and p≤0.05 was considered as the significant level. Results: No significant differences were observed between the two groups. The movement-related measures revealed a main effect of rotation (p˂0.001). However, a significant interaction between direction × planning pattern × group (p˂0.001) indicated a preferential bias for rotatory movements in the medial direction which is consistent with the "medial over lateral advantage". Conclusion: Both left- and right-handed participants had a similar motor planning ability while performing a planning task with their dominant hands. Because our study was behavioral, it only provided a test of the left-hemisphere hypothesis of motor planning.