A test between two hypotheses and a possible third way for the control of prehension

We used an obstacle avoidance task to test two opposing accounts of how the nervous system controls prehension. The visuomotor account supposes that t he system independently controls the grip formation and transport phase of prehensile movements. In contrast, the digit channel hypothesis suggests th at the system controls the thumb and finger more or less independently. Our data strongly favoured the traditional visuomotor channel hypothesis and d emonstrated that the time taken to grasp an object in the presence of obsta cles was well predicted by a Fitts' law relationship. We suggest a "third-w ay" hypothesis in order to retain the advantages of the digit channel hypot hesis within the visuomotor framework. The third-way hypothesis suggests th at the nervous system selects a single digit to transport to the object. We speculate that the actual digit selected might depend upon attention and t he nature of the prehension task. This hypothesis is able to account for mo st of the empirical findings unearthed by researchers investigating the con trol of prehension.