Vibro- and electrotactile user feedback on hand opening for myoelectric forearm prostheses

Many of the currently available myoelectric forearm prostheses stay unused because of the lack of sensory feedback. Vibrotactile and electrotactile stimulation have high potential to provide this feedback. In this study, performance of a grasping task is investigated for different hand opening feedback conditions on 15 healthy subjects and validated on three patients. The opening of a virtual hand was controlled by a scroll wheel. Feedback about hand opening was given via an array of eight vibrotactile or electrotactile stimulators placed on the forearm, relating to eight hand opening positions. A longitudinal and transversal orientation of the array and four feedback conditions were investigated: no feedback, visual feedback, feedback through vibrotactile or electrotactile stimulation, and addition of an extra stimulator for touch feedback. No influence of array orientation was shown for all outcome parameters (duration of the task, the percentage of correct hand openings, the mean position error, and the percentage deviations up to one position). Vibrotactile stimulation enhances the performance compared to the nonfeedback conditions. The addition of touch feedback further increases the performance, but at the cost of an increased duration. The same effects were found for the patient group, but the task duration was around 25% larger.