Mathias Wellner

A View on VR-Enhanced Rehabilitation Robotics

Robot-assisted gait training can increase the duration and number of training sessions, whilst reducing the number of therapists required per patient. However, training can often be boring for the patient so that the training intensity is low. Furthermore, training is usually limited to a single modality, providing only force feedback to guide the movement. Virtual reality (VR) with multimodal displays has the chance to feedback performance information to the patient, augment the training with additional audiovisual features, thus, making the therapy more exciting and increasing patient motivation. In this paper we present results from the literature and preliminary results from our research about novel VR strategies applied to gait and arm therapy. Broad clinical testing is still required to determine its efficacy or effectiveness on patient motivation

Virtual competitors influence rowers

Highly immersive environments for sports simulation can help elucidate if and how athletes perform under high pressure situations. We used a rowing simulator with a CAVE setup to test the influence of virtual competitors on 10 experienced rowers. All participants were using the simulator for the first time. The objective was to assess the degree of presence by quantifying how the actions of the virtual competitors triggered behavioral changes in the experienced rowers. The participants completed a virtual 2000 m race with two competing boats, one being behind and one ahead of the participant. For two trials, each boat would come closer to the participant without overtaking, resulting in four experimental conditions. The behavior of the participants was assessed with biomechanical variables, questionnaires, and an interview after the race. Behavioral changes were detected with statistically significant differences in the extracted variables of oar angles, timing variables, velocities, and work. The results for biomechanical variables indicate individual response patterns depending on perception of competitors and self-confidence. Self-reporting indicated a high degree of presence for most participants. Overall, the experimental paradigm worked but was compromised by perceptive and subjective factors. In future, the setup will be used to investigate rowing performance further with a focus on motor learning and training of pressure situations.

Combining Immersive Virtual Environments with Robot-Aided Gait Training

While robotic rehabilitation devices are gaining popularity in research and clinical use, a possible drawback of these devices is the reduced physical interaction between the therapist and the patient compared to manual training. To compensate for this lack, the device has to assess the patients movements and provide (bio-)feedback to the patient. Furthermore, it could deliver instructions and increase motivation. The design and implementation of an immersive virtual environment for robot-assisted gait training are described that delivers feedback and increases motivation. Subjects can navigate through exchangeable virtual environments by modulating their performance of the left and right leg. Preliminary tests show usability with control subjects. Clinical tests are still required to show applicability in the clinical routine and to test for therapeutic efficacy.

A Study on Sound Feedback in a Virtual Environment for Gait Rehabilitation

For the rehabilitation of stroke and spinal cord injured patients, actuated gait orthoses are used to automate treadmill training. To increase motivation and provide task-specific feedback for these patients, virtual environments are developed and evaluated by many research groups. This paper describes the design, implementation and preliminary evaluation of sound feedback strategies for the actuated gait orthosis LOKOMAT. In the context of an obstacle scenario, the scenario parameters distance and foot height are displayed by sound. An evaluation study with 17 healthy subjects compared no sound feedback (control condition), distance feedback, height feedback, and combined feedback. Visual feedback was present in all conditions. Results indicate that subjects walk faster and hit fewer obstacles when acoustic feedback is present. The findings suggest that acoustic feedback is helpful as a complementary modality and can be applied to a variety of virtual, task-oriented rehabilitation environments.

Does a virtual audience influence rowing

The performance of athletes is often influenced by the presence of an audience. This pressure situation, which is common for competition, cannot be trained for on available simulators. Therefore, a novel rowing simulator with virtual reality technology was developed and evaluated. Ten participants of different skill levels were rowing 3×1000m with positive, neutral, and negative virtual audience tribunes in blocks of random order. The analysis of movement variables, physiological response, questionnaires, and interviews was used to detect differences between audience blocks and adjoining non-audience blocks. Although some participants responded in part to the investigated movement and physiological variables, no reliable effect of any of the audience types could be shown. Interestingly, self-reported measures indicated in general a high degree of realism and presence in the scenario. The explanation for the low incidence of behavioural change is that the virtual audience did not create enough pressure on the participants, although no definite conclusion can be drawn owing to the small sample size.

Using a Robotic Gait Orthosis as Haptic Display - A Perception-Based Optimization Approach

The actuated gait orthosis Lokomat has been developed at University Hospital Balgrist for patients with impairments due to neurological or orthopedic lesions. To enhance rehabilitation with the Lokomat, patient-cooperative techniques have been developed. Patient-cooperative means that the technical system considers the patient intention and efforts rather than imposing any predefined movement or inflexible strategy. It is hypothesized that patient-cooperative techniques have the potential to improve the therapeutic outcome compared to classical rehabilitation strategies. One example for patient-cooperative techniques are immersive, multi-modal scenarios. They can provide task-specific feedback and are expected to increase patients motivation to contribute. One interaction possibility is haptic feedback which can be provided by the gait orthosis to simulate interaction with solid objects. The work described here investigated the potential of the Lokomat to provide haptic feedback. Frequency response measurements under closed-loop conditions were conducted to determine the force and position bandwidths. The final goal was to develop an approach for haptic rendering and optimize its parameters with experiments. Optimization criteria were object hardness and stability during object contact. Results of the bandwidth measurements show that the angle bandwidth is 3 Hz (excitation angle amplitude: 3deg) and the force bandwidth 8 Hz (excitation force amplitude: 10 N). The implemented haptic approach combines an impulsive force component, a penalty force component, and a component for lateral friction force. Best results were achieved for a combination of sine shape impulse, spring constant K with 2000 N/m, and modified damping coefficient B with 300 Ns/m2.

Stepping Over Virtual Obstacles with an Actuated Gait Orthosis

The rehabilitation robot LOKOMAT has been developed at University Hospital Balgrist to automate treadmill training of spinal cord injury and stroke patients. Current rehabilitation training on that robot consists of moving the patients legs on predefined trajectories. However, this kind of training is not challenging, as patients are moved regardless of their efforts and do not see their advancement. To enhance rehabilitation training with the LOKOMAT, a virtual reality setup was installed. It consists of a passive stereo projection system (screen size 3 m times 2 m), a Dolby 5.1 sound system and an electric fan. With that setup an obstacle crossing scenario was implemented. The patients can see their advancement on the screen, as an animated figurine (avatar) moves along a path simultaneously with their own movements. Additionally they can hear sounds (e.g. environmental sounds, steps), feel the wind, and experience force feedback, provided by the orthosis, when hitting obstacles. The objective of a first study on visual feedback was to investigate which feedback suits best to perceive the obstacle distances and heights correctly. To answer this question, 14 healthy subjects walked in the actuated gait orthosis, received visual feedback and tried to avoid collisions with obstacles. Subjects could move freely within the gait orthosis and determine their own speed and step length. They had to cross the obstacles independently, with haptic feedback, indicating obstacle hits. Results show that the side view results in least obstacle hits and that 2D excels 3D display in this respect

Virtual Performance-Enhancing Reality (ViPER) for robot-assisted gait training

Robotic rehabilitation devices become increasingly popular in research and clinical use. One drawback of these devices is the reduced physical interaction between the therapist and the patient compared to manual training. Because of this lack, the device has to assess the patients movements and display this assessment to the patient to give biofeedback, deliver instructions and increase motivation. This paper describes the design and implementation of an immersive virtual environment for robot-assisted gait training that delivers feedback and increases motivation. The subject can navigate through exchangeable virtual rooms and locations by modulating his or her performance of the left and right leg. Preliminary tests show usability with control subjects. Clinical tests are still required to show applicability in the clinical routine and to test for therapeutic efficacy