A Novel Method for Vibrotactile Proprioceptive Feedback Using Spatial Encoding and Gaussian Interpolation

Objective: The bidirectional communication between the user and the prosthesis is an important requirement when developing prosthetic hands. Proprioceptive feedback is fundamental to perceiving prosthesis movement without the need for constant visual attention. We propose a novel solution to encode wrist rotation using a vibromotor array and Gaussian interpolation of vibration intensity. The approach generates tactile sensation that smoothly rotates around the forearm congruently with prosthetic wrist rotation. The performance of this scheme was systematically assessed for a range of parameter values (number of motors and Gaussian standard deviation). Methods: Fifteen able-bodied subjects and one individual with congenital limb deficiency used vibrational feedback to control the virtual hand in the target-achievement test. Performance was assessed by end-point error and efficiency as well as subjective impressions. Results: The results showed a preference for smooth feedback and a higher number of motors (8 and 6 versus 4). With 8 and 6 motors, the standard deviation, determining the sensation spread and continuity, could be modulated through a broad range of values (0.1 - 2) without a significant performance loss (error: ∼ 10%; efficiency: ∼ 30%). For low values of standard deviation (0.1-0.5), the number of motors could be reduced to 4 without a significant performance decrease. Conclusion: The study demonstrated that the developed strategy provided meaningful rotation feedback. Moreover, the Gaussian standard deviation can be used as an independent parameter to encode an additional feedback variable. Significance: The proposed method is a flexible and effective approach to providing proprioceptive feedback while adjusting the trade-off between sensation quality and the number of vibromotors

Doctor of Philosophy

dissertationUpper limb amputees desire an artificial arm that allows for multiple degrees of freedom of control over the movements of the prosthesis, coupled with direct sensory feedback. The goal of this work was to assess if it is feasible to interface artificial limbs to severed nerves of human upper limb amputees. Longitudinal intrafascicular electrodes were interfaced to severed nerve stumps of long-term human amputees. Initial studies conducted for two days following electrode implantation showed that it is possible to provide discrete, unitary, painless, graded sensations of touch, joint movement and position referred to the missing limb. Amputees were able to generate and control motor nerve activity uniquely associated with the missing limb movements. Longer term studies conducted for a period of up to 4 weeks showed recorded motor nerve activity and elicited sensations remained stable and there was no significant change in the stimulation parameters. Finally, amputees were able to control a modified Utah Artificial Arm. Results of our studies show that it is possible to interface an artificial limb to the severed nerves of upper limb amputees. Further work is required to refine the hardware which can be eventually incorporated into the artificial arm, allowing the amputees to wear the prosthesis and more precisely execute movements related to real life activities of daily living

Designing sensory feedback approaches for restoring touch and position feedback in upper limb amputees

Upper limb amputation disrupts most daily activities and reduces the quality of life of affected individuals. Building a suitable prosthetic limb, which can restore at least some of the lost capabilities, is a goal which has been pursued for centuries. In the last few decades, our rapidly expanding understanding of the human nervous system has unlocked impressive advances in artificial limbs. Today, commercial prosthetic hands can be controlled intuitively through voluntary muscle contractions. Nevertheless, despite leaps in the quality of modern prostheses, sensory feedback remains one of the major omissions, forcing users to rely on vision to accomplish basic tasks, such as holding a plastic cup without crushing it. Several sensory feedback strategies have recently been developed to restore tactile and proprioceptive feedback to amputees, demonstrating benefits in important areas, such as higher functional performance and increases in the sense of prosthesis ownership. Sensory feedback strategies can be distinguished based on whether the sensation they restore matches the quality (homologous feedback) or the location (somatotopic feedback) of the original sensation. Despite promising results, somatotopic tactile feedback strategies often result in unnatural sensations (e.g. electricity). Furthermore, restoration of more than a single sensory modality is rarely reported, despite being necessary to create artificial limbs capable of delivering realistic sensorimotor experiences during use. In this work, I proposed three novel and complementary strategies to improve sensory feedback restoration in upper limb prostheses. I begin by describing a non-invasive transcutaneous electrical nerve stimulation (TENS) approach aimed at restoring somatotopic tactile sensations, which is potentially applicable to all trans-radial amputees. This stimulation strategy was shown to lead to high performance during functional tasks, and compared favorably to more invasive approaches, despite a few key differences. Considering that there is no such thing as a one-size-fits-all solution for amputees, I concluded that TENS represents a viable alternative to invasive systems, especially in cases where an implant is not possible or desirable. In the second part, I proposed a sensory substitution approach to multimodal feedback, which delivered somatotopic tactile and remapped proprioceptive feedback simultaneously. This stimulation strategy relied entirely on implantable electrodes, simplifying the overall system by delivering two streams of sensory information with the same device. Using this feedback system, two amputees were able to perform interesting functional tasks, such as understanding the size and compliance of various objects, with high accuracy. Finally, I proposed a novel stimulation technique for sensory feedback designed to desynchronize induced neural activity during electrical stimulation, leading to more biomimetic patterns of activity. I discussed how this strategy could be combined with the results obtained in a recent study which I contributed to, in which we demonstrated that a model based encoding strategy resulted in more natural sensations of touch. This thesis provides evidence that advances in electrical stimulation protocols can lead to more capable prosthetic limbs. These new methods enable the delivery of multimodal, biomimetic sensory feedback and will help bridge the gap between scientific discovery and clinical translation

The future of upper extremity rehabilitation robotics: research and practice

The loss of upper limb motor function can have a devastating effect on people’s lives. To restore upper limb control and functionality, researchers and clinicians have developed interfaces to interact directly with the human body’s motor system. In this invited review, we aim to provide details on the peripheral nerve interfaces and brain‐machine interfaces that have been developed in the past 30 years for upper extremity control, and we highlight the challenges that still remain to transition the technology into the clinical market. The findings show that peripheral nerve interfaces and brain‐machine interfaces have many similar characteristics that enable them to be concurrently developed. Decoding neural information from both interfaces may lead to novel physiological models that may one day fully restore upper limb motor function for a growing patient population.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155489/1/mus26860_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155489/2/mus26860.pd