A Phantom-Sensation Based Paradigm for Continuous Vibrotactile Wrist Guidance in Two-Dimensional Space

Vibrotactile feedback has long been used to improve the human motor learning process through information transfer. However, in most of the approaches described in the literature, only the joint angles of the limb are guided. To guide motions that involve multiple degrees of freedom (DOFs), the user needs to interpret multiple simultaneous vibrotactile cues (at least one cue per joint), which is difficult. In this letter, we guide the position of a user's wrist in space by producing a vibrotactile cue at any place around the wrist by using a vibrotactile illusion known as “Phantom Sensation” (PS). In a user study that involved 10 male participants, the vibrotactile cues produced by PS were reasonably accurately located with an average error of 7.9°. To maintain consistency between the vibrotactile cue location and the global frame, we measured the user's wrist rotation and adjusted the position of the vibrotactile cue accordingly. When rotating their hand, the participants recognized the location of the vibrotactile cue with an average error of 9.3°. By using the proposed feedback paradigm, we guided users' wrists in space under two conceptual mappings (“push” and “pull”). This experiment examined the participants' motion path efficiency (ME), which measures the directness with which the user's wrist moves toward the desired position. The participants reached the desired positions under the vibrotactile feedback alone. The average MEs of the “push” and “pull” mappings were 44.3% and 52.4%, respectively. We will apply the proposed method under the “pull” mapping to guide real life tasks, such as book classification or rehabilitation.