@article{vargas_huang_zhu_hu_2022, title={Evoked Tactile Feedback and Control Scheme on Functional Utility of Prosthetic Hand}, volume={7}, ISSN={["2377-3766"]}, url={http://dx.doi.org/10.1109/lra.2021.3139147}, DOI={10.1109/LRA.2021.3139147}, abstractNote={Fine manual control relies on intricate action-perception coupling to effectively interact with objects. Here, we evaluated how electrically evoked artificial tactile sensation can be integrated into the functional utility of a prosthetic hand. Using different myoelectric-control strategies, participants performed a modified box-and-block task using a prosthetic hand. Transcutaneous nerve stimulation was employed to elicit somatotopic fingertip tactile feedback reflecting prosthetic fingertip forces. This feedback was evoked using an electrode grid placed along the participants’ upper arm targeting the median and ulnar nerve bundles. Myoelectric signals from the finger flexor and extensor controlled the prosthetic joint velocity or position. Participants lifted, held, and transported cubes of varying weights using their minimum grip forces. The results showed that participants exerted lower forces and presented lower number of failed trials (prematurely dropped objects) when feedback was provided with respect to without feedback. We also found that position control required more flexor muscle activation compared with velocity control when tactile feedback was provided. Our findings reveal that non-invasively evoked tactile feedback could be used to effectively enable human-in-the-loop control of a prosthetic hand. The outcomes can provide a platform to characterize the action-perception couplings during prosthetic control, in order to improve user experience and system functionality.}, number={2}, journal={IEEE ROBOTICS AND AUTOMATION LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2022}, month={Apr}, pages={1300–1307} }
 @article{vargas_huang_zhu_hu_2022, title={Object Recognition via Evoked Sensory Feedback during Control of a Prosthetic Hand}, volume={7}, ISSN={["2377-3766"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85118588970&partnerID=MN8TOARS}, DOI={10.1109/LRA.2021.3122897}, abstractNote={Haptic and proprioceptive feedback is critical for sensorimotor integration when we use our hand to perform daily tasks. Here, we evaluated how externally evoked haptic and proprioceptive feedback and myoelectric control strategies affected the recognition of object properties when participants controlled a prosthetic hand. Fingertip haptic sensation was elicited using a transcutaneous nerve stimulation grid to encode the prosthetic's fingertip forces. An array of tactors elicited patterned vibratory stimuli to encode tactile-proprioceptive kinematic information of the prosthetic finger joint. Myoelectric signals of the finger flexor and extensor were used to control the position or velocity of joint angles of the prosthesis. Participants were asked to perform object property (stiffness and size) recognition, by controlling the prosthetic hand with concurrent haptic and tactile-proprioceptive feedback. With the evoked feedback, intact and amputee participants recognized the object stiffness and size at success rates ranging from 50% to 100% in both position and velocity control with no significant difference across control schemes. Our findings show that evoked somatosensory feedback in a non-invasive manner can facilitate closed-loop control of the prosthetic hand and allowed for simultaneous recognition of different object properties. The outcomes can facilitate our understanding on the role of sensory feedback during bidirectional human-machine interactions, which can potentially promote user experience in object interactions using prosthetic hands.}, number={1}, journal={IEEE ROBOTICS AND AUTOMATION LETTERS}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2022}, month={Jan}, pages={207–214} }
 @article{vargas_huang_zhu_kamper_hu_2022, title={Resembled Tactile Feedback for Object Recognition Using a Prosthetic Hand}, volume={7}, ISSN={["2377-3766"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85136090957&partnerID=MN8TOARS}, DOI={10.1109/LRA.2022.3196958}, abstractNote={Tactile feedback in the hand is essential for interaction with objects. Here, we evaluated how artificial tactile sensation affected the recognition of object properties using a myoelectrically controlled prosthetic hand. Electromyogram signals from the flexor and extensor finger muscles were used to continuously control either prosthetic joint velocity or position. Participants grasped objects of varying shape or size using the prosthetic hand. Tactile feedback was evoked by transcutaneous nerve stimulation along the participant's upper arm and modulated based on the prosthetic-object contact force. Multi-channel electrical stimulation targeted the median and ulnar nerve bundles to produce resembled tactile sensations at distinct hand regions. The results showed that participants could gauge the onset timing of tactile feedback to discern object shape and size. We also found that the position-controller led to a greater recognition accuracy of object size compared with velocity-control, potentially due to supplemental joint position information from muscle activation level. Our findings demonstrate that non-invasive tactile feedback can enable effective object shape and size recognition during prosthetic control. The evaluation of tactile feedback across myoelectric controllers can help understand the interplay between sensory and motor pathways involved in the control of assistive devices.}, number={4}, journal={IEEE ROBOTICS AND AUTOMATION LETTERS}, author={Vargas, Luis and Huang, He and Zhu, Yong and Kamper, Derek and Hu, Xiaogang}, year={2022}, month={Oct}, pages={10977–10984} }
 @article{vargas_huang_zhu_hu_2021, title={Closed-loop control of a prosthetic finger via evoked proprioceptive information}, volume={18}, ISSN={["1741-2552"]}, url={http://dx.doi.org/10.1088/1741-2552/ac3c9e}, DOI={10.1088/1741-2552/ac3c9e}, abstractNote={Abstract}, number={6}, journal={JOURNAL OF NEURAL ENGINEERING}, publisher={IOP Publishing}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2021}, month={Dec} }
 @article{vargas_huang_zhu_hu_2021, title={Perception of Static Position and Kinesthesia of the Finger using Vibratory Stimulation}, volume={2021-May}, ISSN={["1948-3546"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85107464376&partnerID=MN8TOARS}, DOI={10.1109/NER49283.2021.9441255}, abstractNote={Proprioception provides information regarding the state of an individual's limb in terms of static position and kinesthesia (dynamic movement). When such feedback is lost or impaired, the performance of dexterous control of our biological limbs or assistive devices tends to deteriorate. In this study, we determined if external vibratory stimulation patterns could allow for the perception of a finger's static position and kinesthesia. Using four tactors and two stimulus levels, eight vibratory settings corresponded to eight discrete finger positions. The transition patterns between these eight settings corresponded to kinesthesia. Three experimental blocks assessed the perception of a finger's static position, speed, and movement (amplitude and direction). Our results demonstrated that both position and kinesthesia could be recognized with over 93% accuracy. The outcomes suggest that vibratory stimulus can inform subjects of static and dynamic aspects of finger proprioception. This sensory stimulation approach can be implemented to improve outcomes in clinical populations with sensory deficits, and to enhance user experience when users interact with assistive devices.}, journal={2021 10TH INTERNATIONAL IEEE/EMBS CONFERENCE ON NEURAL ENGINEERING (NER)}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2021}, pages={1087–1090} }
 @article{vargas_huang_zhu_hu_2021, title={Static and dynamic proprioceptive recognition through vibrotactile stimulation}, volume={18}, ISSN={["1741-2552"]}, url={http://dx.doi.org/10.1088/1741-2552/ac0d43}, DOI={10.1088/1741-2552/ac0d43}, abstractNote={Objective. Proprioceptive information provides individuals with a sense of our limb’s static position and dynamic movement. Impaired or a lack of such feedback can diminish our ability to perform dexterous motions with our biological limbs or assistive devices. Here we seek to determine whether both static and dynamic components of proprioception can be recognized using variation of the spatial and temporal components of vibrotactile feedback. Approach. An array of five vibrotactors was placed on the forearm of each subject. Each tactor was encoded to represent one of the five forearm postures. Vibratory stimulus was elicited to convey the static position and movement of the forearm. Four experimental blocks were performed to test each subject’s recognition of a forearm’s simulated static position, rotational amplitude, rotational amplitude and direction, and rotational speed. Main results. Our results showed that the subjects were able to perform proprioceptive recognition based on the delivered vibrotactile information. Specifically, rotational amplitude recognition resulted in the highest level of accuracy (99.0%), while the recognition accuracy of the static position and the rotational amplitude-direction was the lowest (91.7% and 90.8%, respectively). Nevertheless, all proprioceptive properties were perceived with >90% accuracy, indicating that the implemented vibrotactile encoding scheme could effectively provide proprioceptive information to the users. Significance. The outcomes suggest that information pertaining to static and dynamic aspects of proprioception can be accurately delivered using an array of vibrotactors. This feedback approach could be used to potentially evaluate the sensorimotor integration processes during human–machine interactions, and to improve sensory feedback in clinical populations with somatosensory impairments.}, number={4}, journal={JOURNAL OF NEURAL ENGINEERING}, publisher={IOP Publishing}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2021}, month={Aug} }
 @article{vargas_huang_zhu_hu_2020, title={Object Shape and Surface Topology Recognition Using Tactile Feedback Evoked through Transcutaneous Nerve Stimulation}, volume={13}, ISSN={["2329-4051"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85078214377&partnerID=MN8TOARS}, DOI={10.1109/TOH.2020.2967366}, abstractNote={Tactile feedback is critical for distinguishing different object properties. In this article, we determined if tactile feedback evoked by transcutaneous nerve stimulation can be used to detect objects of different shape and surface topology. To evoke tactile sensation at different fingers, a 2x8 electrode grid was placed along the subject's upper arm, and two concurrent electrical stimulation trains targeted the median and ulnar nerve bundles, which evoked individually modulated sensations at different fingers. Fingertip forces of the prosthetic hand were transformed to stimulation current amplitude. Object shape was encoded based on finger-object contact timing. Surface topology represented by ridge height and spacing was encoded through current amplitude and stimulation time interval, respectively. The elicited sensation allowed subjects to determine object shape with success rates >84%. Surface topology recognition resulted in success rates >81%. Our findings suggest that tactile feedback evoked from transcutaneous nerve stimulation allows the recognition of object shape and surface topology. The ability to recognize these properties may help improve object manipulation and promote fine control of a prosthetic hand.}, number={1}, journal={IEEE TRANSACTIONS ON HAPTICS}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2020}, pages={152–158} }