LAUSR

BACKGROUND Providing real-time haptic feedback is an important, but still not sufficiently explored aspect of use of supernumerary robotic limbs (SRLs). We present a multi-pad electrode for conveying multi-modal proprioceptive and sensory information from SRL to the user's thigh and propose a method for stimuli calibration. METHODS Within two pilot tests we investigated return electrode configuration and active electrode discrimination in three healthy subjects to select the appropriate electrode pad topology. Based on the obtained results and anthropometric data from literature, the electrode was designed to have three branches of 10 pads and two additional pads that can be displaced over/under the electrode branches. The electrode was designed to be connected to the stimulator that allows full multiplexing so that specific branches can serve as common return electrode. To define the procedure for application of this system, the sensation, localization and discomfort thresholds applicable for the novel electrode were determined and analysed in ten subjects. RESULTS The results showed no overlaps between the three thresholds for individual pads, with significantly different average values, suggesting that the selected electrode positioning and design provide good active range of useful current amplitude. The results of the subsequent analysis suggested that the stimuli intensity level of 200% of sensation threshold is the most probable value of the localization threshold. Furthermore, this level ensures low chance (i.e. 0.7%) of reaching the discomfort. CONCLUSIONS We believe that envisioned electrotactile system could serve as a high bandwidth feedback channel that can be easily setup to provide proprioceptive and sensory feedback from supernumerary limbs.