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 the system independently controls the grip formation and transport phase of prehensile movements. In contrast, the digit channel hypothesis suggests that the system controls the thumb and finger more or less independently. Our data strongly favoured the traditional visuomotor channel hypothesis and demonstrated that the time taken to grasp an object in the presence of obstacles was well predicted by a Fitts' law relationship. We suggest a "thirdway" hypothesis in order to retain the advantages of the digit channel hypothesis within the visuomotor framework. The third-way hypothesis suggests that the nervous system selects a single digit to transport to the object. We speculate that the actual digit selected might depend upon attention and the nature of the prehension task. This hypothesis is able to account for most of the empirical findings unearthed by researchers investigating the control of prehension.