Figure 1. Illustration of experimental set-up and trial types.

(a) Participants moved the rectangular tip of a hand-held tool to contact one of two potential targets projected onto a vertical screen. (b) Example two- and one-target configurations showing the hand and hand-held tool at the start position. (c) The nine possible two-target displays and six possible one-target displays. Target displays were made up of three different target types: the supination target requiring a tool-tip angle of 25°, the pronation target requiring a tool-tip angle of −65°, and the ambiguous target that could be comfortably contacted using a tool-tip angle of either 70° (supination) or −110° (pronation). The blue and red boxes highlight key displays in which one of the targets was ambiguous and the other required either supination (blue) or pronation (red).