Figure 1.

a) An opaque curtain is placed between subjects and the testing device to prevent visual observation of the experimental apparatus and experimenter during trials. The curtain ensures that a subject experiences only tactile feedback and cannot see his or her tested hand, which may contain an experimental SWM handle (with filament) or a control handle (with filament removed). (b) A top view of a seated subject. The subject’s dominant hand is inserted through a slit in the curtain, which is covered with an additional flap of curtain fabric to prevent observation of the testing apparatus through gaps around the wrist. The experimenter (not shown) sits opposite to the subject. The curtain prevents the subject from visually observing the experimenter.