*3.2.2. Grasping control*

An additional control experiment was carried out to examine whether the subjects were able to grasp a virtual object using the simulator hand. In this grasping control task, six spheres with different diameters (from 2 mm to 10 cm) were depicted one at a time on a fix position on the simulator screen. The subject was instructed to grasp them with the virtual hand. To give some feedback to the subjects about the virtual force exerted over the sphere, a second index finger was drawn (with a very faint color) in the position the simulated index finger would have been if there was not a solid object in its way.

The results of this experiment were very similar to the ones shown in Figure 8. In this case, we defined the error as the distance between the index fingertip and the surface of the sphere. The average error while subjects tried to hold onto the sphere in the last two trails of each subject was 1.32 mm (s.d. 0.47). For the amputee subject, the average error was 1.77 mm (s.d. 0.63). In conclusion, subjects were able to grasp the object, and to do it in a smooth, natural way. These results prove that the simulator developed in this work is a valid tool for rehabilitation.
