Abstract: BACKGROUND: A prosthetic system should ideally reinstate the bidirectional communication between the user’s brain and its end effector by restoring both motor and sensory functions lost after an amputation. However, current commercial prostheses generally do not incorporate somatosensory feedback. Even without explicit feedback, grasping using a prosthesis partly relies on sensory information. Indeed, the prosthesis operation is characterized by visual and sound cues that could be exploited by the user to estimate the prosthesis state. However, the quality of this incidental feedback has not been objectively evaluated. METHODS: In this study, the psychometric properties of the auditory and visual feedback of prosthesis motion were assessed and compared to that of a vibro-tactile interface. Twelve able-bodied subjects passively observed prosthesis closing and grasping an object, and they were asked to discriminate (experiment I) or estimate (experiment II) the closing velocity of the prosthesis using visual (VIS), acoustic (SND), or combined (VIS + SND) feedback. In experiment II, the subjects performed the task also with a vibrotactile stimulus (VIB) delivered using a single tactor. The outcome measures for the discrimination and estimation experiments were just noticeable difference (JND) and median absolute estimation error (MAE), respectively. RESULTS: The results demonstrated that the incidental sources provided a remarkably good discrimination and estimation of the closing velocity, significantly outperforming the vibrotactile feedback. Using incidental sources, the subjects could discriminate almost the minimum possible increment/decrement in velocity that could be commanded to the prosthesis (median JND < 2% for SND and VIS + SND). Similarly, the median MAE in estimating the prosthesis velocity randomly commanded from the full working range was also low, i.e., approximately 5% in SND and VIS + SND. CONCLUSIONS: Since the closing velocity is proportional to grasping force in state-of-the-art myoelectric prostheses, the results of the present study imply that the incidental feedback, when available, could be usefully exploited for grasping force control. Therefore, the impact of incidental feedback needs to be considered when designing a feedback interface in prosthetics, especially since the quality of estimation using supplemental sources (e.g., vibration) can be worse compared to that of the intrinsic cues.

@article{MCBDS122019, author = {Wilke, Meike Annika and Niethammer, Christian and Meyer, Britta and Farina, Dario and Dosen, Strahinja}, title = {Psychometric characterization of incidental feedback sources during grasping with a hand prosthesis}, journal = {Journal of NeuroEngineering and Rehabilitation}, year = {2019}, month = {dec}, volume = {16}, number = {155}, pages = {155}, doi = {10.1186/s12984-019-0622-9}, month_numeric = {12} }

@inproceedings{CWM052018, author = {Niethammer, Christian and Rosenstiel, Wolfgang and Spüler, Martin}, title = {Robustness of single-hand classification against other-hand activity in EEG}, booktitle = {Proceedings of the 7th International BCI Meeting 2018}, year = {2018}, month = {may}, pages = {28-29}, address = {Asilomar, CA}, month_numeric = {5} }

@article{MC032015, author = {Spüler, Martin and Niethammer, Christian}, title = {Error-related potentials during continuous feedback: using EEG to detect errors of different type and severity}, journal = {Frontiers in Human Neuroscience}, year = {2015}, month = {mar}, volume = {9}, number = {}, pages = {155}, doi = {10.3389/fnhum.2015.00155}, month_numeric = {3} }

@inproceedings{MCWM092014, author = {Spüler, Martin and Niethammer, Christian and Rosenstiel, Wolfgang and Bogdan, Martin}, title = {Classification of error-related potentials in EEG during continuous feedback}, booktitle = {Proceedings of the 6th International Brain-Computer Interface Conference}, year = {2014}, month = {sep}, month_numeric = {9} }