Evaluation of Haptic Sensation and Object Recognition using Transcutaneous Nerve Stimulation

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ABSTRACT Haptic sensory feedback is critical to fine motor control and object recognitions. A loss of this somatosensation can severely affect our ability of dexterous object interaction and manipulation. A majority of prosthetic hand users often rely on substituted sensory information from other sources, such as visual or audio cues. As a result, the prosthetic hand movement is slow, and object grasp/release requires continuous cognitive attention. Recently, direct stimulations of the peripheral nerve or somatosensory cortex via neural implants have shown great promise in evoking somatotopically-matched feedback. However, several major hurdles limit wide clinical applications, including the lack of long-term stability of the implanted system, the surgery procedures coupled with the extensive post-surgery care, and specialized system maintenance. Therefore, there is an urgent need to develop non-invasive approaches that can elicit somatotopically-matched sensations to prosthetic arm users. The objective of my proposed research is to develop non-invasive transcutaneous nerve stimulation approaches that can provide stable haptic feedback to arm amputees and allow them to recognize different object properties (e.g., stiffness, size, shape, and location) from the evoked sensations. The proposed research will facilitate my long-term goal of developing clinically applicable approaches that can enable closed-loop human-machine interactions. Specifically, transcutaneous nerve stimulation can elicit haptic sensations in the phantom hand, by delivering precisely controlled electrical current that can activate proximal segments of the median and ulnar nerves. This approach allows us to activate different portions of the sensory nerve fibers transcutaneously and elicit spatially localized haptic sensations with graded intensity of sensation as shown in our lab. Building on the existing findings, I propose the following research aims: 1) to characterize how the haptic sensations are combined from concurrent nerve stimulations at different locations; and 2) to evaluate the recognition performance of object properties based on elicited haptic sensations with a prosthetic hand. To execute my research aims, I plan to attach a high-density grid electrodes on the medial side of the upper arm beneath the biceps muscle belly. Controlled electrical current with various parameters will then be simultaneously delivered to different pairs of electrodes. The perceived sensations will be quantified, including the changes in spatial location of the sensation and the stability/repeatability of the perceived sensation. I will then deliver current profiles with encoded object properties to different electrode pairs when an articulated prosthetic hand interacts with different objects. The performance of the object recognition will be evaluated. Overall, the outcomes can help deliver accurate and stable haptic sensations to prosthetic hand users, allowing intuitive and closed-loop control, and enhancing embodiment during prosthetic use. The non-invasive nature of my approach also has a great potential for readily clinical translations with a potentially high user-acceptance rate.