Does a complex model help to understand grasping?

Several studies have demonstrated a peculiar effect of initial aperture on the grip formation in reach-to-grasp movements. We compare these findings with the predictions of two models for prehension. The first is a very simple model that only describes the movements of the end-effectors. The second model is rather complex and takes postural constraints into account. Both models can account for many aspects of human grasping when the movement starts with the digits in contact. We compare the models' performance with published data on other initial configurations. Both models predict an effect of initial aperture that was not present in the data. The model that considers postural constraints does not perform better than the simple model. We conclude that such constraints are not responsible for the main characteristics of the reach-to-grasp movement.