Abstract
This study was concerned with the selection criteria used for grip planning in adolescents with left or right hemiparetic cerebral palsy. In the first experiment participants picked up a pencil and placed the tip in a pre-defined target region. We varied the size of the target to test the hypothesis that increased end-point precision demands would favour the use of a grip that affords end-state comfort. In the second experiment we studied grip planning in three task contexts to test the hypothesis that a more functional task context would likewise promote the end-state comfort effect. In both studies we found that when movements were performed with the impaired hand participants with right hemiparesis (i.e., left brain damage) aimed for postural comfort at the start rather than at the end of the object-manipulation phase. Participants with left hemiparesis (i.e., right brain damage), however, did not favour a particular selection criterion with the impaired hand in the first study. When movements were performed with the unimpaired hand, grip selection criteria again differed for right and left hemiparetic participants such that subjects with left hemiparesis showed the end-state comfort effect in all conditions of both experiments, but participants with right hemiparesis only showed the end-state comfort effect in the most functional tasks of the second experiment. From these data we infer that the left hemisphere plays a special role in action planning, as has been recognized before, and that one of the deficits accompanying right hemiparesis is a deficit of movement planning, which has not been recognized before. Our findings have both theoretical and clinical implications which are discussed.
