Valentina Squeri

Self-adaptive robot training of stroke survivors for continuous tracking movements

BackgroundAlthough robot therapy is progressively becoming an accepted method of treatment for stroke survivors, few studies have investigated how to adapt the robot/subject interaction forces in an automatic way. The paper is a feasibility study of a novel self-adaptive robot controller to be applied with continuous tracking movements.MethodsThe haptic robot Braccio di Ferro is used, in relation with a tracking task. The proposed control architecture is based on three main modules: 1) a force field generator that combines a non linear attractive field and a viscous field; 2) a performance evaluation module; 3) an adaptive controller. The first module operates in a continuous time fashion; the other two modules operate in an intermittent way and are triggered at the end of the current block of trials. The controller progressively decreases the gain of the force field, within a session, but operates in a non monotonic way between sessions: it remembers the minimum gain achieved in a session and propagates it to the next one, which starts with a block whose gain is greater than the previous one. The initial assistance gains are chosen according to a minimal assistance strategy. The scheme can also be applied with closed eyes in order to enhance the role of proprioception in learning and control.ResultsThe preliminary results with a small group of patients (10 chronic hemiplegic subjects) show that the scheme is robust and promotes a statistically significant improvement in performance indicators as well as a recalibration of the visual and proprioceptive channels. The results confirm that the minimally assistive, self-adaptive strategy is well tolerated by severely impaired subjects and is beneficial also for less severe patients.ConclusionsThe experiments provide detailed information about the stability and robustness of the adaptive controller of robot assistance that could be quite relevant for the design of future large scale controlled clinical trials. Moreover, the study suggests that including continuous movement in the repertoire of training is acceptable also by rather severely impaired subjects and confirms the stabilizing effect of alternating vision/no vision trials already found in previous studies.

Parkinson's disease accelerates age-related decline in haptic perception by altering somatosensory integration.

This study investigated how Parkinsons disease alters haptic perception and the underlying mechanisms of somatosensory and sensorimotor integration. Changes in haptic sensitivity and acuity (the abilities to detect and to discriminate between haptic stimuli) due to Parkinsons disease were systematically quantified and contrasted to the performance of healthy older and young adults. Using a robotic force environment, virtual contours of various curvatures were presented. Participants explored these contours with their hands and indicated verbally whether they could detect or discriminate between two contours. To understand what aspects of sensory or sensorimotor integration are altered by ageing and disease, we manipulated the sensorimotor aspect of the task: the robot either guided the hand along the contour or the participant actively moved the hand. Active exploration relies on multimodal sensory and sensorimotor integration, while passive guidance only requires sensory integration of proprioceptive and tactile information. The main findings of the study are as follows: first, a decline in haptic precision can already be observed in adults before the age of 70 years. Parkinsons disease may lead to an additional decrease in haptic sensitivity well beyond the levels typically seen in middle-aged and older adults. Second, the haptic deficit in Parkinsons disease is general in nature. It becomes manifest as a decrease in sensitivity and acuity (i.e. a smaller perceivable range and a diminished ability to discriminate between two perceivable haptic stimuli). Third, thresholds during both active and passive exploration are elevated, but not significantly different from each other. That is, active exploration did not enhance the haptic deficit when compared to passive hand motion. This implies that Parkinsons disease affects early stages of somatosensory integration that ultimately have an impact on processes of sensorimotor integration. Our results suggest that the known motor problems in Parkinsons disease that are generally characterized as a failure of sensorimotor integration may, in fact, have a sensory origin.

Wrist Rehabilitation in Chronic Stroke Patients by Means of Adaptive, Progressive Robot-Aided Therapy

Despite distal arm impairment after brain injury is an extremely disabling consequence of neurological damage, most studies on robotic therapy are mainly focused on recovery of proximal upper limb motor functions, routing the major efforts in rehabilitation to shoulder and elbow joints. In the present study we developed a novel therapeutic protocol aimed at restoring wrist functionality in chronic stroke patients. A haptic three DoFs (degrees of freedom) robot has been used to quantify motor impairment and assist wrist and forearm articular movements: flexion/extension (FE), abduction/adduction (AA), pronation/supination (PS). This preliminary study involved nine stroke patients, from a mild to severe level of impairment. Therapy consisted in ten 1-hour sessions over a period of five weeks. The novelty of the approach was the adaptive control scheme which trained wrist movements with slow oscillatory patterns of small amplitude and progressively increasing bias, in order to maximize the recovery of the active range of motion. The primary outcome was a change in the active RoM (range of motion) for each DoF and a change of motor function, as measured by the Fugl-Meyer assessment of arm physical performance after stroke (FMA). The secondary outcome was the score on the Wolf Motor Function Test (WOLF). The FMA score reported a significant improvement (average of 9.33±1.89 points), revealing a reduction of the upper extremity motor impairment over the sessions; moreover, a detailed component analysis of the score hinted at some degree of motor recovery transfer from the distal, trained parts of the arm to the proximal untrained parts. WOLF showed an improvement of 8.31±2.77 points, highlighting an increase in functional capability for the whole arm. The active RoM displayed a remarkable improvement. Moreover, a three-months follow up assessment reported long lasting benefits in both distal and proximal arm functionalities. The experimental results of this preliminary clinical study provide enough empirical evidence for introducing the novel progressive, adaptive, gentle robotic assistance of wrist movements in the clinical practice, consolidating the evaluation of its efficacy by means of a controlled clinical trial.

Adaptive regulation of assistance ‘as needed’ in robot-assisted motor skill learning and neuro-rehabilitation

We propose a general adaptive procedure to select the appropriate degree of assistance based on a Bayesian mechanism used to estimate psychophysical thresholds. This technique does not need an accurate model of learning and recovery processes. This procedure is validated in the context of a motor skill learning problem (control of a virtual object), in which the controller is used to gradually increase task difficulty as learning proceeds. These automatic adjustments of task difficulty or the degree of assistance can be used to promote not only motor skill learning but also neuromotor recovery.

Integrating proprioceptive assessment with proprioceptive training of stroke patients

Although proprioceptive impairment is likely to affect in a significant manner the capacity of stroke patients to recover functionality of the upper limb, clinical assessment methods in current use are rather crude, with a low level of reliability and a limited capacity to discriminate the relevant features of the deficits. In this paper we describe a new technique based on robot technology, with the goal of providing a reliable, accurate, quantitative evaluation of the position sense in peri-personal space. The proposed technique uses a bimanual, planar robot manipuladum (BdF device), whose handles are grasped by the blindfolded patient: the paretic hand is passively placed in one of 17 positions and the subject is asked to actively match the paretic hand position in space with the other hand. The position sense of the paretic arm and the corresponding deficit of space representation are characterized by means of 7 indicators: 1) positional error; 2) holding force; 3) medio/lateral shift; 4) antero/posterior shift; 5) medio/lateral skew; 6) antero/posterior skew; 7) shrink coefficient. We also show how the same experimental setup can be used for “proprioceptive training”, i.e. for providing robot assistance to the paretic arm that may improve the position sense of the patient. A preliminary, feasibility test has been carried out with one patient and three controls.

Motor commands in children interfere with their haptic perception of objects

Neural processes of sensory-motor- and motor-sensory integration link perception and action, forming the basis for human interaction with the environment. Haptic perception, the ability to extract object features through action, is based on these processes. To study the development of motor-sensory integration, children judged the curvature of virtual objects after exploring them actively or while guided passively by a robot. Haptic acuity reached adult levels only at early adolescence. Unlike in adults, haptic precision in children was consistently lower during active exploration when compared to passive motion. Thus, the exploratory movements themselves constitute a form of noise for the developing haptic system that younger brains cannot compensate until mid-adolescence. Computationally, this is consistent with a noisy efference copy mechanism producing imprecise predicted sensory feedback, which compromises haptic precision in children, while the mature mechanism aids the adult brain to account for the effect of self-generated motion on perception.

Predicted sensory feedback derived from motor commands does not improve haptic sensitivity

Haptic perception is based on the integration of afferent proprioceptive and tactile signals. A further potential source of information during active touch is predicted sensory feedback (PSF) derived from a copy of efferent motor commands that give rise to the exploratory actions. There is substantial evidence that PSF is important for predicting the sensory consequences of action, but its role in perception is unknown. Theoretically, PSF leads to a higher redundancy of haptic information, which should improve sensitivity of the haptic sense. To investigate the effect of PSF on haptic precision, blindfolded subjects haptically explored the curved contour of a virtual object generated by a robotic manipulandum. They either actively moved their hand along the contour, or their hand was moved passively by the device along the same contour. In the active condition afferent sensory information and PSF were present, while in the passive condition subjects relied solely on afferent information. In each trial, two stimuli of different curvature were presented. Subjects needed to indicate which of the two was more “curved” (forced choice). For each condition, the detection and three discrimination thresholds were computed. The main finding is that absence of efference copy information did not systematically degrade haptic acuity. This indirectly implies that PSF does not aid or enhance haptic perception. We conclude that when maximum haptic sensitivity is required to explore novel objects, the perceptual system relies primarily on afferent tactile and proprioceptive information, and PSF has no added effect on the precision of the perceptual estimate.

Force-Field Compensation in a Manual Tracking Task

This study addresses force/movement control in a dynamic “hybrid” task: the master sub-task is continuous manual tracking of a target moving along an eight-shaped Lissajous figure, with the tracking error as the primary performance index; the slave sub-task is compensation of a disturbing curl viscous field, compatibly with the primary performance index. The two sub-tasks are correlated because the lateral force the subject must exert on the eight-shape must be proportional to the longitudinal movement speed in order to perform a good tracking. The results confirm that visuo-manual tracking is characterized by an intermittent control mechanism, in agreement with previous work; the novel finding is that the overall control patterns are not altered by the presence of a large deviating force field, if compared with the undisturbed condition. It is also found that the control of interaction-forces is achieved by a combination of arm stiffness properties and direct force control, as suggested by the systematic lateral deviation of the trajectories from the nominal path and the comparison between perturbed trials and catch trials. The coordination of the two sub-tasks is quickly learnt after the activation of the deviating force field and is achieved by a combination of force and the stiffness components (about 80% vs. 20%), which is a function of the implicit accuracy of the tracking task.

Robot-assisted training of the kinesthetic sense: enhancing proprioception after stroke

Proprioception has a crucial role in promoting or hindering motor learning. In particular, an intact position sense strongly correlates with the chances of recovery after stroke. A great majority of neurological patients present both motor dysfunctions and impairments in kinesthesia, but traditional robot and virtual reality training techniques focus either in recovering motor functions or in assessing proprioceptive deficits. An open challenge is to implement effective and reliable tests and training protocols for proprioception that go beyond the mere position sense evaluation and exploit the intrinsic bidirectionality of the kinesthetic sense, which refers to both sense of position and sense of movement. Modulated haptic interaction has a leading role in promoting sensorimotor integration, and it is a natural way to enhance volitional effort. Therefore, we designed a preliminary clinical study to test a new proprioception-based motor training technique for augmenting kinesthetic awareness via haptic feedback. The feedback was provided by a robotic manipulandum and the test involved seven chronic hemiparetic subjects over 3 weeks. The protocol included evaluation sessions that consisted of a psychometric estimate of the subject’s kinesthetic sensation, and training sessions, in which the subject executed planar reaching movements in the absence of vision and under a minimally assistive haptic guidance made by sequences of graded force pulses. The bidirectional haptic interaction between the subject and the robot was optimally adapted to each participant in order to achieve a uniform task difficulty over the workspace. All the subjects consistently improved in the perceptual scores as a consequence of training. Moreover, they could minimize the level of haptic guidance in time. Results suggest that the proposed method is effective in enhancing kinesthetic acuity, but the level of impairment may affect the ability of subjects to retain their improvement in time.

Proprioceptive assessment of the wrist joint across both joint degrees of freedom

Neurological movement disorders such as stroke or sensory neuropathy are associated with somatosensory deficits. From a neurorehabilitation perspective, the assessment of proprioceptive function is important for planning and applying adequate rehabilitation treatments. Numerous behavioral and psychophysical methods are available to measure proprioceptive acuity. However, no universally accepted and adopted protocol exists. In recent years robotic devices have increasingly been used to investigate and assess proprioceptive function, but few studies have focused on the wrist joint. To fill this knowledge gap, this study aimed to systematically map the proprioceptive acuity of the wrist for its two joint degrees of freedom (DoF) - flexion/extension (FE) and abduction/adduction (AA). Twenty eight healthy young adults performed an ipsilateral, active joint position matching task using a robotic device. As a measure of proprioceptive acuity we determined the error between target position and the matched joint position. Results showed that: first, proprioceptive acuity varied between the two joint DoF with the matching error for AA being lower than the FE. Second, within each DoF, the motion direction did not affect the accuracy. Third, the radial component of the matching error showed DoF dependence: the FE movements tended to undershoot, while the AA movement overshot the target position. Results are indicative of a joint DoF dependent anisotropy of wrist proprioceptive acuity.