Figure 6.

The PGA, slopes relating PGA to target size (b_PGA), the final grip aperture (FGA), and the slopes relating the FGA to the target size (b_FGA) across the four tasks. (A) The overall PGA increased when a mirror was used (G_M–H) rather than a pane of glass (G_G–H) for target-directed grasps with haptic feedback. For grasps directed a virtual targets, removing haptic feedback (G_M–NH) reduced the PGA. The PGA was reduced further for the real-time pantomimed grasps (RPG_NH). For each task the mean PGA for each target size is plotted for each participant. Evidently, denying haptic feedback increased the slopes. (B) The participants’ b_PGAs (open circles) and the mean b_PGA (dashes) for each task. The b_PGAs for G_M–H were smaller than those for G_G–H, indicating a significant role for online visual feedback of the hand and limb. The b_PGAs were larger, however, whenever haptic feedback was denied, regardless of whether the grasps were target-directed (G_M–NH) or not (RPG_NH). (C) The overall FGA was reduced when haptic feedback was not available. Plotted for each task is the mean FGA for each target size for each participant. Even in the absence of haptic feedback, the FGAs were well-related to target size. (D) The b_FGA (open circles) did not differ amongst the four tasks. Note that the error bars reflect 95% confidence intervals extracted from the mean square error term from the rmANOVA (corrected for violations of sphericity where appropriate).