Assessing walking ability using a robotic gait trainer: opportunities and limitations of assist-as-needed control in spinal cord injury.

BACKGROUND: Walking impairments are a common consequence of neurological disorders and are assessed with clinical scores that suffer from several limitations. Robot-assisted locomotor training is becoming an established clinical practice. Besides training, these devices could be used for assessing walking ability in a controlled environment. Here, we propose an adaptive assist-as-needed (AAN) control for a treadmill-based robotic exoskeleton, the Lokomat, that reduces the support of the device (body weight support and impedance of the robotic joints) based on the ability of the patient to follow a gait pattern displayed on screen. We hypothesize that the converged values of robotic support provide valid and reliable information about individuals' walking ability. METHODS: Fifteen participants with spinal cord injury and twelve controls used the AAN software in the Lokomat twice within a week and were assessed using clinical scores (10MWT, TUG). We used a regression method to identify the robotic measure that could provide the most relevant information about walking ability and determined the test-retest reliability. We also checked whether this result could be extrapolated to non-ambulatory and to unimpaired subjects. RESULTS: The AAN controller could be used in patients with different injury severity levels. A linear model based on one variable (robotic knee stiffness at terminal swing) could explain 74% of the variance in the 10MWT and 61% in the TUG in ambulatory patients and showed good relative reliability but poor absolute reliability. Adding the variable 'maximum hip flexor torque' to the model increased the explained variance above 85%. This did not extend to non-ambulatory nor to able-bodied individuals, where variables related to stance phase and to push-off phase seem more relevant. CONCLUSIONS: The novel AAN software for the Lokomat can be used to quantify the support required by a patient while performing robotic gait training. The adaptive software might enable more challenging training conditions tuned to the ability of the individuals. While the current implementation is not ready for assessment in clinical practice, we could demonstrate that this approach is safe, and it could be integrated as assist-as-needed training, rather than as assessment. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02425332.

A Two Joint Neck Model to Identify Malposition of the Head Relative to the Thorax.

Neck pain is a frequent health complaint. Prolonged protracted malpositions of the head are associated with neck pain and headaches and could be prevented using biofeedback systems. A practical biofeedback system to detect malpositions should be realized with a simple measurement setup. To achieve this, a simple biomechanical model representing head orientation and translation relative to the thorax is introduced. To identify the parameters of this model, anthropometric data were acquired from eight healthy volunteers. In this work we determine (i) the accuracy of the proposed model when the neck length is known, (ii) the dependency of the neck length on the body height, and (iii) the impact of a wrong neck length on the models accuracy. The resulting model is able to describe the motion of the head with a maximum uncertainty of 5 mm only. To achieve this high accuracy the effective neck length must be known a priory. If however, this parameter is assumed to be a linear function of the palpable neck length, the measurement error increases. Still, the resulting accuracy can be sufficient to identify and monitor a protracted malposition of the head relative to the thorax.

Robot-aided assessment of lower extremity functions: a review.

The assessment of sensorimotor functions is extremely important to understand the health status of a patient and its change over time. Assessments are necessary to plan and adjust the therapy in order to maximize the chances of individual recovery. Nowadays, however, assessments are seldom used in clinical practice due to administrative constraints or to inadequate validity, reliability and responsiveness. In clinical trials, more sensitive and reliable measurement scales could unmask changes in physiological variables that would not be visible with existing clinical scores.In the last decades robotic devices have become available for neurorehabilitation training in clinical centers. Besides training, robotic devices can overcome some of the limitations in traditional clinical assessments by providing more objective, sensitive, reliable and time-efficient measurements. However, it is necessary to understand the clinical needs to be able to develop novel robot-aided assessment methods that can be integrated in clinical practice.This paper aims at providing researchers and developers in the field of robotic neurorehabilitation with a comprehensive review of assessment methods for the lower extremities. Among the ICF domains, we included those related to lower extremities sensorimotor functions and walking; for each chapter we present and discuss existing assessments used in routine clinical practice and contrast those to state-of-the-art instrumented and robot-aided technologies. Based on the shortcomings of current assessments, on the identified clinical needs and on the opportunities offered by robotic devices, we propose future directions for research in rehabilitation robotics. The review and recommendations provided in this paper aim to guide the design of the next generation of robot-aided functional assessments, their validation and their translation to clinical practice.

Increasing patient engagement during virtual reality-based motor rehabilitation.

OBJECTIVE: To investigate the influence of different design characteristics of virtual reality exercises on engagement during lower extremity motor rehabilitation. DESIGN: Correlational study. SETTING: Spinal cord injury (SCI) rehabilitation center. PARTICIPANTS: Subjects with SCI (n=12) and control subjects (n=10). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Heart rate and electromyographic activity from both legs at the tibialis anterior, the gastrocnemius medialis, the rectus femoris, and the biceps femoris were recorded. RESULTS: Interactivity (ie, functionally meaningful reactions to motor performance) was crucial for the engagement of subjects. No significant differences in engagement were found between exercises that differed in feedback frequency, explicit task goals, or aspects of competition. CONCLUSIONS: Functional feedback is highly important for the active participation of patients during robotic-assisted rehabilitation. Further investigations on the design characteristics of virtual reality exercises are of great importance. Exercises should thoroughly be analyzed regarding their effectiveness, while user preferences and expectations should be considered when designing virtual reality exercises for everyday clinical motor rehabilitation.

Validation of a mechanism to balance exercise difficulty in robot-assisted upper-extremity rehabilitation after stroke.

BACKGROUND: The motivation of patients during robot-assisted rehabilitation after neurological disorders that lead to impairments of motor functions is of great importance. Due to the increasing number of patients, increasing medical costs and limited therapeutic resources, clinicians in the future may want patients to practice their movements at home or with reduced supervision during their stay in the clinic. Since people only engage in an activity and are motivated to practice if the outcome matches the effort at which they perform, an augmented feedback application for rehabilitation should take the cognitive and physical deficits of patients into account and incorporate a mechanism that is capable of balancing i.e. adjusting the difficulty of an exercise in an augmented feedback application to the patient's capabilities. METHODS: We propose a computational mechanism based on Fitts' Law that balances i.e. adjusts the difficulty of an exercise for upper-extremity rehabilitation. The proposed mechanism was implemented into an augmented feedback application consisting of three difficulty conditions (easy, balanced, hard). The task of the exercise was to reach random targets on the screen from a starting point within a specified time window. The available time was decreased with increasing condition difficulty. Ten subacute stroke patients were recruited to validate the mechanism through a study. Cognitive and motor functions of patients were assessed using the upper extremity section of the Fugl-Meyer Assessment, the modified Ashworth scale as well as the Addenbrookes cognitive examination-revised. Handedness of patients was obtained using the Edinburgh handedness inventory. Patients' performance during the execution of the exercises was measured twice, once for the paretic and once for the non-paretic arm. Results were compared using a two-way ANOVA. Post hoc analysis was performed using a Tukey HSD with a significance level of p < 0.05. RESULTS: Results show that the mechanism was capable of balancing the difficulty of an exercise to the capabilities of the patients. Medians for both arms show a gradual decrease and significant difference of the number of successful trials with increasing condition difficulty (F(2;60) = 44.623; p < 0.01; η(2) = 0.623) but no significant difference between paretic and non-paretic arm (F(1;60) = 3.768; p = 0.057; η(2) = 0.065). Post hoc analysis revealed that, for both arms, the hard condition significantly differed from the easy condition (p < 0.01). In the non-paretic arm there was an additional significant difference between the balanced and the hard condition (p < 0.01). Reducing the time to reach the target, i.e., increasing the difficulty level, additionally revealed significant differences between conditions for movement speeds (F(2;59) = 6.013; p < 0.01; η(2) = 0.185), without significant differences for hand-closing time (F(2;59) = 2.620; p = 0.082; η(2) = 0.09), reaction time (F(2;59) = 0.978; p = 0.383; η(2) = 0.036) and hand-path ratio (F(2;59) = 0.054; p = 0.947; η(2) = 0.002). The evaluation of a questionnaire further supported the assumption that perceived performance declined with increased effort and increased exercise difficulty leads to frustration. CONCLUSIONS: Our results support that Fitts' Law indeed constitutes a powerful mechanism for task difficulty adaptation and can be incorporated into exercises for upper-extremity rehabilitation.

Influence of virtual reality soccer game on walking performance in robotic assisted gait training for children.

BACKGROUND: Virtual reality (VR) offers powerful therapy options within a functional, purposeful and motivating context. Several studies have shown that patients' motivation plays a crucial role in determining therapy outcome. However, few studies have demonstrated the potential of VR in pediatric rehabilitation. Therefore, we developed a VR-based soccer scenario, which provided interactive elements to engage patients during robotic assisted treadmill training (RAGT). The aim of this study was to compare the immediate effect of different supportive conditions (VR versus non-VR conditions) on motor output in patients and healthy control children during training with the driven gait orthosis Lokomat*. METHODS: A total of 18 children (ten patients with different neurological gait disorders, eight healthy controls) took part in this study. They were instructed to walk on the Lokomat in four different, randomly-presented conditions: (1) walk normally without supporting assistance, (2) with therapists' instructions to promote active participation, (3) with VR as a motivating tool to walk actively and (4) with the VR tool combined with therapists' instructions. The Lokomat gait orthosis is equipped with sensors at hip and knee joint to measure man-machine interaction forces. Additionally, subjects' acceptance of the RAGT with VR was assessed using a questionnaire. RESULTS: The mixed ANOVA revealed significant main effects for the factor CONDITIONS (p < 0.001) and a significant interaction CONDITIONS x GROUP (p = 0.01). Tests of between-subjects effects showed no significant main effect for the GROUP (p = 0.592). Active participation in patients and control children increased significantly when supported and motivated either by therapists' instructions or by a VR scenario compared with the baseline measurement "normal walking" (p < 0.001). CONCLUSIONS: The VR scenario used here induces an immediate effect on motor output to a similar degree as the effect resulting from verbal instructions by the therapists. Further research needs to focus on the implementation of interactive design elements, which keep motivation high across and beyond RAGT sessions, especially in pediatric rehabilitation.

Concurrent validity and reliability of a mobile tracking technology to measure angular and linear movements of the neck.

The neck can be moved in six degrees of freedom. Current 3D-optoelectronic motion-capture systems capable of measuring these movements are inappropriate for use in clinical practice because they are stationary, expensive and time-consuming. We therefore developed a less complex 3D-tracking technology based on Steam®VR to measure six degrees of freedom in a clinical setting. The aim of this study was to assess the validity and reliability of this system. The developed prototype consists of two infrared-emitting lighthouses and sensors, mounted on the participant's helmet and trunk belt, to detect the orientation of the head and trunk. The system was evaluated by means of an infrared light-reflecting marker tracking system. Twenty healthy participants, equipped with these sensors and markers, performed thirteen neck movement tasks. Linear and angular movements were measured. These tasks were repeated after six to eight days to assess test-retest reliability. Concurrent validity was assessed by the root mean square error, and reliability with generalizability theory. With an average root mean square error between 1.2 and 2.0° in angular and 0.4-0.5 cm in linear movements, the prototype was shown to precisely track these movements. Reliability of the prototype and the reference system was comparable for all tasks. A high contribution of participant's variability to the observed variance was generally detected, with the exception of joint repositioning error and upper cervical flexion. The reliability was task-specific and did not differ between the systems. The prototype system was shown to be valid, although the reliability of the repositioning and upper cervical flexion tests needs to be reconsidered.

Standardized voluntary force measurement in a lower extremity rehabilitation robot.

BACKGROUND: Isometric force measurements in the lower extremity are widely used in rehabilitation of subjects with neurological movement disorders (NMD) because walking ability has been shown to be related to muscle strength. Therefore muscle strength measurements can be used to monitor and control the effects of training programs. A new method to assess isometric muscle force was implemented in the driven gait orthosis (DGO) Lokomat. To evaluate the capabilities of this new measurement method, inter- and intra-rater reliability were assessed. METHODS: Reliability was assessed in subjects with and without NMD. Subjects were tested twice on the same day by two different therapists to test inter-rater reliability and on two separate days by the same therapist to test intra-rater reliability. RESULTS: Results showed fair to good reliability for the new measurement method to assess isometric muscle force of lower extremities. In subjects without NMD, intraclass correlation coefficients (ICC) for inter-rater reliability ranged from 0.72 to 0.97 and intra-rater reliability from 0.71 to 0.90. In subjects with NMD, ICC ranged from 0.66 to 0.97 for inter-rater and from 0.50 to 0.96 for intra-rater reliability. CONCLUSION: Inter- and intra- rater reliability of an assessment method for measuring maximal voluntary isometric muscle force of lower extremities was demonstrated. We suggest that this method is a valuable tool for documentation and controlling of the rehabilitation process in patients using a DGO.

Virtual gait training for children with cerebral palsy using the Lokomat gait orthosis.

The Lokomat gait orthosis was developed in the Spinal Cord Injury Center at the University Hospital Balgrist Zurich and provides automatic gait training for patients with neurological gait impairments, such as Cerebral Palsy (CP). Each patient undergoes a task-oriented Lokomat rehabilitation training program via a virtual reality setup. In four virtual scenarios, the patient is able to exercise tasks such as wading through water, playing soccer, overstepping obstacles or training in a street scenario, each task offering varying levels of difficulty. Patients provided positive feedback in reference to the utilized haptic method, specifically addressing the sufficient degree of realism. In a single case study, we verified the task difficulty.

An Adaptive and Hybrid End-Point/Joint Impedance Controller for Lower Limb Exoskeletons.

Assist-as-needed (AAN) algorithms for the control of lower extremity rehabilitation robots can promote active participation of patients during training while adapting to their individual performances and impairments. The implementation of such controllers requires the adaptation of a control parameter (often the robot impedance) based on a performance (or error) metric. The choice of how an adaptive impedance controller is formulated implies different challenges and possibilities for controlling the patient's leg movement. In this paper, we analyze the characteristics and limitations of controllers defined in two commonly used formulations: joint and end-point space, exploring especially the implementation of an AAN algorithm. We propose then, as a proof-of-concept, an AAN impedance controller that combines the strengths of working in both spaces: a hybrid joint/end-point impedance controller. This approach gives the possibility to adapt the end-point stiffness in magnitude and direction in order to provide a support that targets the kinematic deviations of the end-point with the appropriate force vector. This controller was implemented on a two-link rehabilitation robot for gait training-the Lokomat®Pro V5 (Hocoma AG, Switzerland) and tested on 5 able-bodied subjects and 1 subject with Spinal Cord Injury. Our experiments show that the hybrid controller is a feasible approach for exoskeleton devices and that it could exploit the benefits of the end-point controller in shaping a desired end-point stiffness and those of the joint controller to promote the correct angular changes in the trajectories of the joints. The adaptation algorithm is able to adapt the end-point stiffness based on the subject's performance in different gait phases, i.e., the robot can render a higher stiffness selectively in the direction and gait phases where the subjects perform with larger kinematic errors. The proposed approach can potentially be generalized to other robotic applications for rehabilitation or assistive purposes.

Biofeedback for robotic gait rehabilitation.

BACKGROUND: Development and increasing acceptance of rehabilitation robots as well as advances in technology allow new forms of therapy for patients with neurological disorders. Robot-assisted gait therapy can increase the training duration and the intensity for the patients while reducing the physical strain for the therapist. Optimal training effects during gait therapy generally depend on appropriate feedback about performance. Compared to manual treadmill therapy, there is a loss of physical interaction between therapist and patient with robotic gait retraining. Thus, it is difficult for the therapist to assess the necessary feedback and instructions. The aim of this study was to define a biofeedback system for a gait training robot and test its usability in subjects without neurological disorders. METHODS: To provide an overview of biofeedback and motivation methods applied in gait rehabilitation, previous publications and results from our own research are reviewed. A biofeedback method is presented showing how a rehabilitation robot can assess the patients' performance and deliver augmented feedback. For validation, three subjects without neurological disorders walked in a rehabilitation robot for treadmill training. Several training parameters, such as body weight support and treadmill speed, were varied to assess the robustness of the biofeedback calculation to confounding factors. RESULTS: The biofeedback values correlated well with the different activity levels of the subjects. Changes in body weight support and treadmill velocity had a minor effect on the biofeedback values. The synchronization of the robot and the treadmill affected the biofeedback values describing the stance phase. CONCLUSION: Robot-aided assessment and feedback can extend and improve robot-aided training devices. The presented method estimates the patients' gait performance with the use of the robot's existing sensors, and displays the resulting biofeedback values to the patients and therapists. The therapists can adapt the therapy and give further instructions to the patients. The feedback might help the patients to adapt their movement patterns and to improve their motivation. While it is assumed that these novel methods also improve training efficacy, the proof will only be possible with future in-depth clinical studies.

Patient-cooperative strategies for robot-aided treadmill training: first experimental results.

Task-oriented repetitive movements can improve motor performance in patients with neurological or orthopaedic lesions. The application of robotics and automation technology can serve to assist, enhance, evaluate, and document neurological and orthopedic rehabilitation. This paper deals with the application of "patient-cooperative" techniques to robot-aided gait rehabilitation of neurological disorders. We define patient-cooperative to mean that, during movement, the technical system takes into account the patient's intention and voluntary efforts rather than imposing any predefined movements or inflexible strategies. It is hypothesized that such cooperative robotic approaches can improve the therapeutic outcome compared to classical rehabilitation strategies. New cooperative strategies are presented that detect the patient's voluntary efforts. First, this enables the patient increased freedom of movement by a certain amount of robot compliance. Second, the robot behavior adapts to the existing voluntary motor abilities. And third, the robotic system displays and improves the patient contribution by visual biofeedback. Initial experimental results are presented to evaluate the basic principle and technical function of proposed approaches. Further improvements of the technical design and additional clinical testing is required to prove whether the therapeutic outcome can be enhanced by such cooperative strategies.

Neural activity in the primate superior colliculus and saccadic reaction times in double-step experiments.

Although primates including humans can do 2-3 saccades per second while observing their environment, this seems to be more complicated when the same visual target is displaced twice in brief succession. When the subject has to follow this target with its gaze, the reaction time of the second saccade is longer than that of the first. We present data from electrophysiological recordings in the superior colliculus of a monkey that is performing a double-step saccade task. Analysis of the neuronal activity shows that the fixation neurons and the saccadic neurons respond differently in single- and double-step tasks. Fixation neurons are not as active between the two saccades as could be expected from single-step trials. Therefore, the fixation neurons are not likely to cause the increase in reaction time. The recorded saccadic neurons usually showed a presumably visual activation about 70 ms after target appearance and a motor burst starting briefly before the saccade. A target-aligned response was encountered in half of the neurons about 150 ms after the second target appearance. The early visual target-aligned response is often lost before the second saccade in a double-step task with short stimulus delay. The rise of activity was slower before the second than before the first saccade. The neural latency was therefore longer before the second saccade. The motor burst coincides with the second saccade although it is delayed. Thus, the motor burst was always predictive of the occurrence of the saccade. We conclude that the fixation neurons in the superior colliculus are not likely to cause the delay of the second saccade, and that the activity in the saccadic neurons in the superior colliculus encodes the timing of the second saccade even if it is delayed.

Path control: a method for patient-cooperative robot-aided gait rehabilitation.

Gait rehabilitation robots are of increasing importance in neurorehabilitation. Conventional devices are often criticized because they are limited to reproducing predefined movement patterns. Research on patient-cooperative control strategies aims at improving robotic behavior. Robots should support patients only as much as needed and stimulate them to produce maximal voluntary efforts. This paper presents a patient-cooperative strategy that allows patients to influence the timing of their leg movements along a physiologically meaningful path. In this "path control" strategy, compliant virtual walls keep the patient's legs within a "tunnel" around the desired spatial path. Additional supportive torques enable patients to move along the path with reduced effort. Graphical feedback provides visual training instructions. The path control strategy was evaluated with 10 healthy subjects and 15 subjects with incomplete spinal cord injury. The spatio-temporal characteristics of recorded kinematic data showed that subjects walked with larger temporal variability with the new strategy. Electromyographic data indicated that subjects were training more actively. A majority of iSCI subjects was able to actively control their gait timing. Thus, the strategy allows patients to train walking while being helped rather than controlled by the robot.

Influence of task predictability on the activity of neurons in the rostral superior colliculus during double-step saccades.

Target probability has been shown to modulate motor preparatory activity of neurons in the caudal superior colliculus (SC) of the primate. Here we tested whether top-down processes, such as task predictability, influence the activity of neurons also at the rostral pole of the SC (rSC), classically related to fixation. To investigate this, double-step saccade tasks were embedded in two different paradigms, one containing unpredictable and another containing predictable tasks. During predictable tasks the animals could develop some expectation about the forthcoming second target jump, i.e., anticipate when and where to make the second saccade. Neuronal responses were recorded during both paradigms and compared, revealing the influence of task predictability on the activity of rSC neurons during specific periods of fixation. In particular, neuronal activity stayed significantly lower during the fixation period between two successive saccades in predictable than in unpredictable tasks. In addition there was a learning effect within a session during predictable conditions, i.e., the intersaccadic activity was higher in the early than in the late trials. Further, reaction times for the second saccade were shorter in predictable than in unpredictable tasks. However, we demonstrated that this difference in reaction times cannot be solely accounted for by the reported difference in neural activity, which was mainly influenced by the predictability of the tasks. With these results we show that top-down processes such as predictability are imposed on the activity of neurons in the rostral pole of the primate SC.

Assessment of walking performance in robot-assisted gait training: a novel approach based on empirical data.

Motivation and voluntary drive of patients can be improved by applying biofeedback during robot-assisted rehabilitation trainings. Biofeedback systems were traditionally based on theoretical assumptions. In this paper, we present a novel approach to calculate biofeedback during robot-assisted gait training. Our method was based on empirical data that were obtained from healthy subjects when simulating distinctive degrees of walking performance during robot-assisted gait training. This empirical data-based biofeedback (EDBF) method was evaluated with 18 subjects without gait disorders. A higher correlation between the subjects' walking performance and biofeedback values was found for the EDBF method compared to a theory-based biofeedback approach.

Swing phase resistance enhances flexor muscle activity during treadmill locomotion in incomplete spinal cord injury.

BACKGROUND: This study investigated whether loading the legs during the swing phase of walking enhances flexor muscle activity in ambulatory patients with incomplete spinal cord injury (SCI). METHODS: Nine patients had surface electromyography (EMG) and joint kinematics recorded from the lower extremities during treadmill walking. Swing phase loading of the legs was achieved by weights (1-3 kg) attached to each lower extremity or by a velocity-dependent resistance applied by the Lokomat robotic gait orthosis. RESULTS: When patients walked with the weights, there was a consistent increase in the activity of the knee flexors and sometimes of hip or ankle flexor activity during swing. Similarly, when the robot applied the velocity-dependent resistance during walking, swing phase flexor EMG activity tended to be greater. Enhanced knee flexion was observed in all patients after the weights or the robot-generated resistance was removed. CONCLUSIONS: Flexor muscle activity during swing can be enhanced through additional proprioceptive input in patients with incomplete SCI with brief aftereffects. Further testing of this strategy is necessary to determine if it can improve the gait of ambulatory patients.

Computerized visual feedback: an adjunct to robotic-assisted gait training.

BACKGROUND AND PURPOSE: Robotic devices for walking rehabilitation allow new possibilities for providing performance-related information to patients during gait training. Based on motor learning principles, augmented feedback during robotic-assisted gait training might improve the rehabilitation process used to regain walking function. This report presents a method to provide visual feedback implemented in a driven gait orthosis (DGO). The purpose of the study was to compare the immediate effect on motor output in subjects during robotic-assisted gait training when they used computerized visual feedback and when they followed verbal instructions of a physical therapist. SUBJECTS: Twelve people with neurological gait disorders due to incomplete spinal cord injury participated. METHODS: Subjects were instructed to walk within the DGO in 2 different conditions. They were asked to increase their motor output by following the instructions of a therapist and by observing visual feedback. In addition, the subjects' opinions about using visual feedback were investigated by a questionnaire. RESULTS: Computerized visual feedback and verbal instructions by the therapist were observed to result in a similar change in motor output in subjects when walking within the DGO. Subjects reported that they were more motivated and concentrated on their movements when using computerized visual feedback compared with when no form of feedback was provided. DISCUSSION AND CONCLUSION: Computerized visual feedback is a valuable adjunct to robotic-assisted gait training. It represents a relevant tool to increase patients' motor output, involvement, and motivation during gait training, similar to verbal instructions by a therapist.

Human-centered robotics applied to gait training and assessment.

Robot-aided gait training can increase the duration and number of training sessions while reducing the number of therapists required for each patient. However, current automated gait trainers do not adapt their movement to the patient's muscular efforts and passive musculoskeletal properties. Furthermore, robot-aided training without therapists lacks the feedback required for patient assessment. In this article, we present results from the literature and our research to provide an overview of novel human-centered strategies for robot behaviors that are patient-cooperative and support motor-function assessment. Combining robot-aided training with robot-aided assessment will likely make future gait therapy easier, more comfortable, and more efficient. Broad clinical testing is still required for proving this assumption.

Arm movement and gap as factors influencing the reaction time of the second saccade in a double-step task.

To guide our hand for reaching, we explore our visual environment by sequences of saccades. In the present paper, we studied the eye and hand movements of human subjects looking or looking and pointing at a target that is instantaneously displaced two times (double-step task). It was previously shown that the second saccade has a much longer reaction time than the first one [Feinstein & Williams (1972) Vision Res., 12, 33-44]. The second reaction time is even longer if the subject also has to point to the target with the hand [Lünenburger et al. (2000) Eur. J. Neurosci., 12, 4107-4116]. The conditions and objective for these effects are further examined in the present paper. It is shown that vision of the hand reduces the first and second saccadic reaction times in parallel. The second reaction time is prolonged for shorter delays between both target steps as well as for larger amplitudes of the second saccade. However, the long second reaction time does not reflect an absolute saccadic refractory period, because a gap before the second target step reduces the second reaction time to a value similar to the first. Hand response time and average hand velocity were increased when the second target step was larger. The response time for the eyes was about 30% of the response time of the hand. We argue that the observed effects reflect the coordination of eye and hand movement to allow a precise and efficient reaching behaviour.