A Review of Non-Invasive Haptic Feedback stimulation Techniques for Upper Extremity Prostheses <s> Non-Invasive Hybrid Feedback Stimulation Techniques <s> We present the results of experiments to compare vibration and skin stretch in a virtual proprioception task in which subjects used a force sensor to control the movement of a virtual aim. Pilot experiments pointed to the need to provide the arm with varying dynamics (like a real arm) and to scale the feedback from vibratory and skin stretch displays to demonstrate a clear improvement in the accuracy of movement. For the final experiments, ten subjects were first trained on the system with visual feedback and then tested with vibratory feedback, skin stretch feedback and no feedback. Both vibration and skin stretch improved the subjects' performance. For some subjects, a second no-feedback case showed improvement over the initial case, indicating learning; in other cases, the no- feedback performance deteriorated and subjects reported that they had become used to relying on feedback. Overall, skin stretch provided superior results, particularly when the virtual arm was in a low-inertia configuration and at low velocity. The results suggest that small skin-stretch devices could be worn on the body to provide useful proprioceptive information when interacting with virtual environments and in motion training for rehabilitation or sports. <s> BIB001 </s> A Review of Non-Invasive Haptic Feedback stimulation Techniques for Upper Extremity Prostheses <s> Non-Invasive Hybrid Feedback Stimulation Techniques <s> This work assesses the ability of transradial amputees to discriminate multi-site tactile stimuli in sensory discrimination tasks. It compares different sensory feedback modalities using an artificial hand prosthesis in: 1) a modality matched paradigm where pressure recorded on the five fingertips of the hand was fed back as pressure stimulation on five target points on the residual limb; and 2) a modality mismatched paradigm where the pressures were transformed into mechanical vibrations and fed back. Eight transradial amputees took part in the study and were divided in two groups based on the integrity of their phantom map; group A had a complete phantom map on the residual limb whereas group B had an incomplete or nonexisting map. The ability in localizing stimuli was compared with that of 10 healthy subjects using the vibration feedback and 11 healthy subjects using the pressure feedback (in a previous study), on their forearms, in similar experiments. Results demonstrate that pressure stimulation surpassed vibrotactile stimulation in multi-site sensory feedback discrimination. Furthermore, we demonstrate that subjects with a detailed phantom map had the best discrimination performance and even surpassed healthy participants for both feedback paradigms whereas group B had the worst performance overall. Finally, we show that placement of feedback devices on a complete phantom map improves multi-site sensory feedback discrimination, independently of the feedback modality. <s> BIB002 </s> A Review of Non-Invasive Haptic Feedback stimulation Techniques for Upper Extremity Prostheses <s> Non-Invasive Hybrid Feedback Stimulation Techniques <s> This paper presents a new multi-modal haptic device designed to deliver sensory feedback to upper limb amputees using a myoelectric prosthesis. In particular this device conveys to the individual information about (i) contact between digits and the environment through a vibrotactile stimulus and (ii) grip force applied by the prosthesis on objects via force/pressure feedback. The device described in this work may be used both in research and clinical scenarios in the near future due to its limited dimensions, weight and power consumption. <s> BIB003 </s> A Review of Non-Invasive Haptic Feedback stimulation Techniques for Upper Extremity Prostheses <s> Non-Invasive Hybrid Feedback Stimulation Techniques <s> This paper proposes a teleimpedance controller with tactile feedback for more intuitive control of the Pisa/IIT SoftHand. With the aim to realize a robust, efficient and low-cost hand prosthesis design, the SoftHand is developed based on the motor control principle of synergies, through which the immense complexity of the hand is simplified into distinct motor patterns. Due to the built-in flexibility of the hand joints, as the SoftHand grasps, it follows a synergistic path while allowing grasping of objects of various shapes using only a single motor. The DC motor of the hand incorporates a novel teleimpedance control in which the user’s postural and stiffness synergy references are tracked in real-time. In addition, for intuitive control of the hand, two tactile interfaces are developed. The first interface (mechanotactile) exploits a disturbance observer which estimates the interaction forces in contact with the grasped object. Estimated interaction forces are then converted and applied to the upper arm of the user via a custom made pressure cuff. The second interface employs vibrotactile feedback based on surface irregularities and acceleration signals and is used to provide the user with information about the surface properties of the object as well as detection of object slippage while grasping. Grasp robustness and intuitiveness of hand control were evaluated in two sets of experiments. Results suggest that incorporating the aforementioned haptic feedback strategies, together with user-driven compliance of the hand, facilitate execution of safe and stable grasps, while suggesting that a low-cost, robust hand employing hardware-based synergies might be a good alternative to traditional myoelectric prostheses. <s> BIB004 </s> A Review of Non-Invasive Haptic Feedback stimulation Techniques for Upper Extremity Prostheses <s> Non-Invasive Hybrid Feedback Stimulation Techniques <s> While substantial research efforts have been put forth to advance the mechatronics and control of prosthetic hands, little attention has been paid to restoring the sensory functions of tactile feedback to amputees. It is known that the human hand when unable to feel through either disease or induced anesthesia becomes incapable of performing a number of essential dexterous tasks. Therefore, it is proposed that prosthetic hands without these capabilities will be no better. Tactile sensing in the human hand can be used for both autonomous reflexes and conscious perception. In a previous study we had explored using tactile sensing for autonomous reflexes to enable fragile object grasping [1], in this study we evaluate the benefits and performance in conscious perception of force, vibration and thermal tactile information. A prosthetic hand equipped with a BioTac sensor (capable of sensing force, vibration and temperature) and different tactors developed to play back these feedback modalities on a subject's forearm were used to evaluate perception in tactile discrimination experiments. Results showed that this system is able to effectively convey information to the prosthesis user to identify and differentiate objects of different weight, temperature, thermal properties, or surface texture when they were placed between the subject's prosthetic fingertips. While this system was effective at providing useful perceptual feedback, the subject indicated that the majority of the tactors were distracting and would be undesirable for day-to-day use. <s> BIB005 </s> A Review of Non-Invasive Haptic Feedback stimulation Techniques for Upper Extremity Prostheses <s> Non-Invasive Hybrid Feedback Stimulation Techniques <s> A novel wearable haptic device for modulating contact forces at the fingertip is presented. Rendering of forces by skin deformation in three degrees of freedom (DoF), with contact—no contact capabilities, was implemented through rigid parallel kinematics. The novel asymmetrical three revolute-spherical-revolute (3-RSR) configuration allowed compact dimensions with minimum encumbrance of the hand workspace. The device was designed to render constant to low frequency deformation of the fingerpad in three DoF, combining light weight with relatively high output forces. A differential method for solving the non-trivial inverse kinematics is proposed and implemented in real time for controlling the device. The first experimental activity evaluated discrimination of different fingerpad stretch directions in a group of five subjects. The second experiment, enrolling 19 subjects, evaluated cutaneous feedback provided in a virtual pick-and-place manipulation task. Stiffness of the fingerpad plus device was measured and used to calibrate the physics of the virtual environment. The third experiment with 10 subjects evaluated interaction forces in a virtual lift-and-hold task. Although with different performance in the two manipulation experiments, overall results show that participants better controlled interaction forces when the cutaneous feedback was active, with significant differences between the visual and visuo-haptic experimental conditions. <s> BIB006 </s> A Review of Non-Invasive Haptic Feedback stimulation Techniques for Upper Extremity Prostheses <s> Non-Invasive Hybrid Feedback Stimulation Techniques <s> Haptic interfaces are mechatronic devices designed to render tactile sensations; although they are typically based on robotic manipulators external to the human body, recently, interesting wearable solutions have been presented. Toward a more realistic feeling of virtual and remote environment interactions, we propose a novel wearable skin stretch device for the upper limb called “hBracelet.” It consists of two main parts coupled with a linear actuator. Each part contains two servo actuators that move a belt. The device is capable of providing distributed mechanotactile stimulation on the arm by controlling the tension and the distance of the two belts in contact with the skin. When the motors spin in opposite directions, the belt presses into the user's arm, while when they spin in the same direction, the belt applies a shear force to the skin. Moreover, the linear actuator exerts longitudinal cues on the arm by moving the two parts of the device. In this letter, we illustrate the mechanical structure, working principle, and control strategies of the proposed wearable haptic display. We also present a qualitative experiment in a teleoperation scenario as a case study to demonstrate the effectiveness of the proposed haptic interface and to show how a human can take advantage of multiple haptic stimuli provided at the same time and on the same body area. The results show that the device is capable of successfully providing information about forces acting at the remote site, thus, improving telepresence. <s> BIB007
Several previous studies investigated how to use the simultaneous application of two or more different types of haptic feedback to influence the human sensory perception, where such system is called the hybrid feedback stimulation system. From those studies, the hybrid system has shown better performance than of each separate feedback type  . For example, combining the squeeze and the skin stretch feedback displays convey the feeling of the contact pressure during grasping objects smoothly to the patient's brain BIB007 . A short outline of the works on hybrid feedback stimulation display is presented in Table 7 . In BIB002 , authors investigated the ability of the amputees to discriminate multi-site tactile stimuli in sensory refinement tasks. Two main challenges were faced in this study. The first one is to provide the pressure sensing that occurs on the prosthetic fingertips directly to the subjects' brain as a pressure stimulation on their residual forearm; it is called multi-site mechano-tactile (MT) display. The second challenge is to use the vibration feedback display to convey the contact pressure feeling to the amputees; it is called a multi-site vibrotactile (VT) display. Results showed that there is no significant difference in the display of the MT feedback and VT feedback, but with a simple superior in preference of MT system over the VT system. This is due to the fact that the volunteers, who have a good response due to the MT system, are also showing high stimulation level when excited with the VT system. The prosthetic hand extended with force sensors on each fingertip was displayed in Fig. 10 . a, while the VT and MT actuators were presented in Fig. 10 . b and 10. c, respectively. A similar comparison study between the vibration and skin stretch feedback stimulations has been presented in BIB001 to investigate which of them gives better performance in providing the virtual proprioception task. The benchtop skin stretch device and C2 vibrational tactor were used as a skin stretch display and vibration display, respectively. The evaluation tests with ten healthy participants showed that the skin stretch gave superior results than the vibration display, especially at the low-inertia configuration and at low velocity. On the other hand, a novel small size, lightweight, low power consumption preliminary prototype of a hybrid feedback device has been designed in BIB003 . The new multi-modal haptic device consists of the pressure and vibration feedback stimulators to provide useful tactile information to the users of prosthetic hand about the grasping force and the contact pressure, respectively. The validation tests showed that the hybrid haptic device has an acceptable design and prepareness for future experiment tests with the amputees volunteers. Moreover, the functionality of utilizing a multimode haptic device to increase the performance of Pisa/IIT SoftHand to the execution of safe and stable grasps was confirmed by using a hybrid feedback system with two displays BIB004 . The first display is a squeeze stimulator for rendering the grasping force, while the second display is a vibration stimulator for detecting the surface texture and the object's slippage. A novel minimizing size, lightweight, and low-frequency deformation wearable haptic device with 3 DoF for rendering contact forces at the fingertip has been developed BIB006 . HK-282A RC servo motors were utilized to create the mechanical movement of 3-RSR asymmetric rigid parallel kinematics, as shown in Fig. 11 . Depending on three evaluation tests, it can be concluded that the ability of the participants to manipulate, grasp, and lift a virtual object was increased when using the haptic device. Lastly, a BioTac sensor was integrated with the prosthetic hand to detect the contact force, surface texture, and the objects' temperature at the same time BIB005 . A hybrid haptic device of pressure, vibration, and thermal feedback displays was used to convey the tactile information to the users' skin. The overall results confirmed that the proposed hybrid wearable device is capable to convey the tactile information to the patients of upper limb amputation in an effective manner, where the contact pressure, temperature, thermal properties, and surface texture, which occurs on between the prosthetic hand and the objects at the same time can be discriminated. 