More actions in bimanual action sequences increase variability in hand preference: End-state comfort, beginning-state comfort, trade-offs, and pre-crastination in reaching movements in action sequences of varying complexity

Hand preference is not a stable trait across tasks and may change depending on several variables, including the task’s context. In our study, we investigated how hand preference in a bimanual task varies depending on the task’s context, task complexity, and the proximity of the objects to be handled. Fifty right-handed participants performed action sequences of different complexity, defined as the number of actions in the sequence. They lifted a bottle from a table, either (a) to give it to the experimenter, (b) to screw off the cap, and place the bottle and cap back on the table or (c) to screw the cap off, drink from the bottle, screw the cap back on, and place the bottle back on the table. Each sequence was performed five times, in a counterbalanced manner, with the bottle placed on the table in one of five positions: far left, near left, central, near right, and far right. The results suggest that hand preference indeed fluctuates within and between action sequences. Given the impossibility of planning action sequences so that all actions are always performed with the hand usually preferred for the action, due to trade-offs individuals have to compromise by sacrificing either their end- or beginning-state comfort by performing some actions with the typically non-preferred hand. In such cases, individuals may shift the handled object between hands in order to facilitate the subsequent action, possibly owing to pre-crastination. In our study, the number of such shifts increased with the number of elements in the action sequence.