Tactile Feedback in Upper Limb Prosthetics: A Pilot Study on Trans-Radial Amputees Comparing Different Haptic Modalities.

Despite technological advancements, upper limb prostheses still face high abandonment/rejection rates due to limitations in control interfaces and the absence of force/tactile feedback. Improving these aspects is crucial for enhancing user acceptance and optimizing functional performance. This pilot study, therefore, aims to understand which sensory feedback in combination with a soft robotic prosthetic hand could provide advantages for amputees, including performing everyday tasks. Tactile cues provided are contact information, grasping force, degree of hand opening, and combinations of this information. To transfer such feedback, different wearable systems are used, based on either vibrotactile or force stimulation in a non-invasive modality matching approach. Five volunteers with a trans-radial amputation controlling the new prosthetic hand SoftHand Pro performed a study protocol including everyday tasks. The results indicate the preference of amputees for a single, i.e. non-combined, feedback modality. The choice of appropriate haptic feedback seems to be subject and task-specific. Furthermore, in alignment with the participants' feedback, force feedback, with adequate granularity and clarity, could potentially be the most valuable feedback among those presented. Finally, the study suggests that prosthetic solutions should be preferred where amputees are able to choose their feedback system.

Design and Validation of the Readable Device: A Single-Cell Electromagnetic Refreshable Braille Display.

Blindness represents one of the major disabling societal causes, impacting the life of visually impaired people and their families. For what concerns the access to written information, one of the main tools used by blind people is the traditional Braille code. This is the reason why in the recent years, there has been a technological effort to develop refreshable Braille devices. These consist of multiple physical dots that dynamically change their configuration to reproduce different sequences of the letters in Braille code. Although promising, these approaches have many drawbacks, which are mainly related to costs, design complexity, portability, and power consumption. Of note, while many solutions have been proposed for multi-cell devices, the investigation of the potentialities of single-cell refreshable systems has received little attention so far. This investigation could offer effective and viable manners to overcome the aforementioned drawbacks, likely fostering a widespread adoption of such assistive technologies with end-users. In this article, we present the design and characterization of a new cost-effective single-cell Electromagnetic Refreshable Braille Display, the Readable system. We also report on tests performed with blindfolded and blind expert Braille code readers. Results demonstrate the effectiveness of our device in correctly reproducing alphanumeric content, opening promising perspectives in every-day life applications.

An Objective Functional Evaluation of Myoelectrically-Controlled Hand Prostheses: A Pilot Study Using the Virtual Peg Insertion Test.

Assessing upper limb prostheses and their influence when performing goal-directed activities is essential to compare the quality of different devices and optimize their control settings. Currently available assessments are often subjective, insensitive, and cannot provide a detailed evaluation of prostheses and their usage. The goal of this pilot study was to explore the feasibility of using the Virtual Peg Insertion Test (VPIT) to provide an in-depth assessment of a prosthesis and its functional performance. One transradial amputee performed the goal-directed manipulation task of the VPIT with the sound body side and four different myoelectrically-controlled prostheses. The subject was able to complete the VPIT protocol successfully with technically advanced prosthesis (two out of four devices). The kinematic- and kinetic-based objective evaluation measures extracted from the VPIT were able to capture clear differences between the sound and amputated body side and were able to identify varying movement patterns for different prostheses. Additionally, the outcome measures were sensitive to changes in prosthesis control settings and showed clear trends across measures of subjectively perceived prosthesis quality assessed through a questionnaire. This work demonstrates the general feasibility of objectively evaluating functional prosthesis usage with the VPIT.

SoftHand at the CYBATHLON: a user's experience.

BACKGROUND: Roughly one-quarter of upper limb prosthesis users reject their prosthesis. Reasons for rejection range from comfort, to cost, aesthetics, function, and more. This paper follows a single user from training with and testing of a novel upper-limb myoelectric prosthesis (the SoftHand Pro) for participation in the CYBATHLON rehearsal to training for and competing in the CYBATHLON 2016 with a figure-of-nine harness controlled powered prosthesis (SoftHand Pro-H) to explore the feasibility and usability of a flexible anthropomorphic prosthetic hand. METHODS: The CYBATHLON pilot took part in multiple in-lab training sessions with the SoftHand Pro and SoftHand Pro-H; these sessions focused on basic control and use of the prosthetic devices and direct training of the tasks in the CYBATHLON. He used these devices in competition in the Powered Arm Prosthesis Race in the CYBATHLON rehearsal and 2016 events. RESULTS: In training for the CYBATHLON rehearsal, the subject was able to quickly improve performance with the myoelectric SHP despite typically using a body-powered prosthetic hook. The subject improved further with additional training using the figure-of-nine harness-controlled SHPH in preparation for the CYBATHLON. The Pilot placed 3rd (out of 4) in the rehearsal. In the CYBATHLON, he placed 5th (out of 12) and was one of only two pilots who successfully completed all tasks in the competition, having the second-highest score overall. CONCLUSIONS: Results with the SoftHand Pro and Pro-H suggest it to be a viable alternative to existing anthropomorphic hands and show that the unique flexibility of the hand is easily learned and exploited.

Postural Hand Synergies during Environmental Constraint Exploitation.

Humans are able to intuitively exploit the shape of an object and environmental constraints to achieve stable grasps and perform dexterous manipulations. In doing that, a vast range of kinematic strategies can be observed. However, in this work we formulate the hypothesis that such ability can be described in terms of a synergistic behavior in the generation of hand postures, i.e., using a reduced set of commonly used kinematic patterns. This is in analogy with previous studies showing the presence of such behavior in different tasks, such as grasping. We investigated this hypothesis in experiments performed by six subjects, who were asked to grasp objects from a flat surface. We quantitatively characterized hand posture behavior from a kinematic perspective, i.e., the hand joint angles, in both pre-shaping and during the interaction with the environment. To determine the role of tactile feedback, we repeated the same experiments but with subjects wearing a rigid shell on the fingertips to reduce cutaneous afferent inputs. Results show the persistence of at least two postural synergies in all the considered experimental conditions and phases. Tactile impairment does not alter significantly the first two synergies, and contact with the environment generates a change only for higher order Principal Components. A good match also arises between the first synergy found in our analysis and the first synergy of grasping as quantified by previous work. The present study is motivated by the interest of learning from the human example, extracting lessons that can be applied in robot design and control. Thus, we conclude with a discussion on implications for robotics of our findings.