Abstract
Tactile feedback about, at least, hand aperture and grasping force, is required for (1) optimal control of a myoelectric forearm prosthesis, (2) to reduce the burden on the visual system and (3) to enable more subconscious use of the prosthesis. In this thesis, the possibilities of vibrotactile and electrotactile stimulation to provide this feedback to the user are investigated. Vibrotactile stimulation was preferred over electrotactile stimulation, because it is more comfortable and did not increase task durations. Several stimulation configurations (longitudinal vs. transversal oriented arrays and amplitude vs. frequency modulation, etc.) and different vibrotactile stimulators (an array of little coin motors and a C2 tactor) have been compared in virtual grasping tasks. Most of the investigated options resulted in increased grasping performances compared to situations without feedback, with no large differences between the evaluated configurations and stimulators. Subsequently, hand aperture and grasping force feedback were successfully combined in one system and it was shown that this combination also enabled discrimination of object stiffness. Experiments that are more related to daily life practice were set up by adding distractive counting tasks, by incorporating EMG control, by including upper-limb loss subjects and finally by evaluating grasping performance in daily life grasping tasks performed with a real myoelectric forearm prosthesis. Distractive tasks and EMG control did not reduce the grasping performance with vibrotactile feedback and no differences in grasping performance with vibrotactile feedback were found between healthy subjects and upper limb loss subjects. It was shown that vibrotactile feedback about hand aperture and grasping force can increase the grasping performance with a real myoelectric forearm prosthesis (for example in object identification) in situations where sight on the prosthesis is blocked. However, when visual feedback is available, no effect of the vibrotactile feedback was found after a short period of use, although subjects did perceive the feedback as helpful.
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