Fig. 1.

Experiment design. 1A: Lateral view with the participant sitting approximately 60 cm from the laptop and approximately 2 m from the Optotrak camera. 1B: Experimental set up from the front view, with a plain light blue board placed behind the participant and the hand visible to both the Optotrak camera and the laptop camera. 1C: The positions of the LED sensors with one secured on the index fingertip, one on the thumb-tip and one over the radial styloid process, each secured with adhesive tape. In this position, the sensors were visible to the Optotrak camera but not to the laptop camera, so as not to interfere with DLC video image analysis.