Jaka Ziherl

Pick to place trajectories in human arm training environment

This paper presents a new method of trajectory planning in rehabilitation robotics. First were measured in healthy subject the pick to place trajectories while haptic robot is in zero impedance space. B-spline approximation is used to mathematically define the measured paths. This trajectory path serves as a central line for the rounding haptic tunnel. In addition to radial elastic and damping force an optional guidance force can be applied along the tunnel to reach the place point. The B-spline control points were observed around the robot and arm workspace. The trajectory path defined with B-splines is compared with minimum jerk and minimum torque defined trajectories. Finally are compared the pick to place movements with and without tunnel use in healthy subject and in stroke hemiplegic patient.

Measuring motor actions and psychophysiology for task difficulty estimation in human-robot interaction

In this paper, we describe a method for estimating task difficulty in human-robot interaction using a combination of motor actions and psychophysiology. A number of variables are calculated from kinematics, dynamics, heart rate, skin conductance, respiration and skin temperature. Discriminant analysis of the variables is used to determine whether the user finds the task too easy or too hard. The discriminant function is recursively updated with Kalman filtering in order to better adapt to the current user. The method was tested offline in a task with 20 subjects. In cross-validation, nonadaptive discriminant analysis yielded a classification accuracy of 80.2% while adaptive discriminant analysis yielded a classification accuracy of 84.3%.

Psychophysiological responses to robot training in different recovery phases after stroke

Psychophysiological responses have become a valuable tool in human-robot interaction since they provide an objective estimate of the users psychological state. Unfortunately, their usefulness in rehabilitation robotics is uncertain since they are influenced by both physical activity and pathological conditions such as stroke. We performed psychophysiological measurements in subacute and chronic stroke patients as well as healthy controls during a reaching and grasping exercise task performed in a multimodal virtual environment. Furthermore, we evaluated the differences in kinematic and static parameters between the three groups of subjects. The results of the observed kinematic and static evaluation parameters showed significant differences when different assistive modes enabled the subject to focus on a particular function of the exercise, like reaching or grasping, or coordinated actions that combine reaching and grasping, reflecting the motor abilities of the individual. The analysis of psychophysiological responses suggests that both chronic and subacute stroke subjects have weaker psychophysiological responses than healthy subjects, though the responses of chronic patients have recovered somewhat. This certainly indicates that further studies are needed before psychophysiological responses can be used in clinical practice.

Challenges in biocooperative rehabilitation robotics

Psychological states such as mood, motivation and engagement are known to be critical for the success of rehabilitation, and encouraging unmotivated stroke patients improves the likelihood of their eventual recovery. Psychological factors can be incorporated into the closed-loop control of biocooperative rehabilitation systems, augmenting the device with critical information about the patient state. However, in rehabilitation robotics, interpretation of psychophysiological measurements is made complex by the multi-task environment, the presence of strenuous physical activity and patients damage to the central and autonomic nervous systems. The study examines these challenges and proposes possible solutions for implementation in biocooperative control of rehabilitation robots.

River multimodal scenario for rehabilitation robotics

This paper presents the novel “River” multimodal rehabilitation robotics scenario that includes video, audio and haptic modalities. Elements contributing to intrinsic motivation are carefully joined in the three modalities to increase motivation of the user. The user first needs to perform a motor action, then receives a cognitive challenge that is solved with adequate motor activity. Audio includes environmental sounds, music and spoken instructions or encouraging statements. Sounds and music were classified according to the arousal-valence space. The haptic modality can provide catching, grasping, tunnel or adaptive assistance, all depending on the users needs. The scenario was evaluated in 16 stroke users, who responded to it favourably according to the Intrinsic Motivation Inventory questionnaire. Additionally, the river multimodal environment seems to elicit higher motivation than a simpler apple pick-and-place multimodal task.

Cognitive demand in a VR-enriched arm training and its relation to performance, motivation and cognitive abilities

Nowadays virtual reality (VR) is a common tool in neurorehabilitation. However, developing scenarios that maximize therapeutic outcome remains an ongoing challenge. In a virtual scenario with varying cognitive complexity, this study investigated the influence of cognitive abilities, arousal and motivation on movement training. Results show that cognitive demand is a crucial factor for controlling motivation and performance in a virtual reality-enriched motor training with stroke patients.

Robotic rehabilitation tasks and measurements of psychophysiological responses

Rehabilitation robots, together with vision and audio systems form the multimodal environment for exercising the person in a number of ways, unavoidably influencing the physiological state of the subject. This paper examines viability of measuring psycho physiological responses to different robotic tasks. The heart rate, skin conductance, respiration and peripheral skin temperature were observed to verify if physical activity obstructs useful recordings and to verify responses in stroke population. 30 healthy subjects were checked with a control task, a purely mental task and task with physical load. 23 subacute stroke persons did a control task, pick and place task (+ inverted version) and Stroop test, same as 22 healthy control subjects. Psycho physiological measurements yielded results even in the presence of physical load and can thus potentially be useful for rehabilitation robotics. Similar responses as in healthy control group were found in the stroke group. Skin conductance response frequency, respiratory rate, skin conductance and skin temperature (all changes from baseline) were confirmed as parameters signaling changes in arousal and valence of both, stroke and control groups.

Haptic assistance in virtual environments for motor rehabilitation

This paper presents the MIMICS MMS rehabilitation system with a virtual rehabilitation task that includes several modes of haptic assistance. We observed the influence of these different modes of assistance on task performance and work performed toward the target during the pick-and-place movement. Twenty-three hemiparetic subjects and a control group of twentythree subjects participated in the study. The haptic assistance resulted in improved task performance and lower work performed during pick-and-place movement.