Proportional EMG Control of Ankle Plantar Flexion in a Powered Transtibial Prosthesis

The human calf muscle generates 80% of the mechanical work to walk throughout stance-phase, powered plantar flexion. Powered plantar flexion is not only important for walking energetics, but also to minimize the impact on the leading leg at heel-strike. For unilateral transtibial amputees, it has recently been shown that knee load on the leading, intact limb decreases as powered plantar flexion in the trailing prosthetic ankle increases. Not surprisingly, excessive loads on the leading, intact knee are believed to be causative of knee osteoarthritis, a leading secondary impairment in lowerextremity amputees. In this study, we hypothesize that a transtibial amputee can learn how to control a powered anklefoot prosthesis using a volitional electromyographic (EMG) control to directly modulate ankle powered plantar flexion. We here present preliminary data, and find that an amputee participant is able to modulate toe-off angle, net ankle work and peak power across a broad range of walking speeds by volitionally modulating calf EMG activity. The modulation of these key gait parameters is shown to be comparable to the dynamical response of the same powered prosthesis controlled intrinsically (No EMG), suggesting that transtibial amputees can achieve an adequate level of powered plantar flexion controllability using direct volitional EMG control.United States. Dept. of Defense (award number 6920559)United States. Dept. of Defense (award number 6920877)Swiss National Science Foundation (grant PBELP3_140656

Distinct locomotor control and awareness in awake sleepwalkers

Sleepwalking is a common parasomnia permitting complex actions to occur outside of consciousness. Kannape et al. show that, also in awake behaviour, sleepwalkers have a different level of conscious awareness when walking under cognitive load, mimicking nocturnal sleepwalking episodes

Cognitive loading affects motor awareness and movement kinematics but not locomotor trajectories during goal-directed walking in a virtual reality environment.

The primary purpose of this study was to investigate the effects of cognitive loading on movement kinematics and trajectory formation during goal-directed walking in a virtual reality (VR) environment. The secondary objective was to measure how participants corrected their trajectories for perturbed feedback and how participants' awareness of such perturbations changed under cognitive loading. We asked 14 healthy young adults to walk towards four different target locations in a VR environment while their movements were tracked and played back in real-time on a large projection screen. In 75% of all trials we introduced angular deviations of ±5° to ±30° between the veridical walking trajectory and the visual feedback. Participants performed a second experimental block under cognitive load (serial-7 subtraction, counter-balanced across participants). We measured walking kinematics (joint-angles, velocity profiles) and motor performance (end-point-compensation, trajectory-deviations). Motor awareness was determined by asking participants to rate the veracity of the feedback after every trial. In-line with previous findings in natural settings, participants displayed stereotypical walking trajectories in a VR environment. Our results extend these findings as they demonstrate that taxing cognitive resources did not affect trajectory formation and deviations although it interfered with the participants' movement kinematics, in particular walking velocity. Additionally, we report that motor awareness was selectively impaired by the secondary task in trials with high perceptual uncertainty. Compared with data on eye and arm movements our findings lend support to the hypothesis that the central nervous system (CNS) uses common mechanisms to govern goal-directed movements, including locomotion. We discuss our results with respect to the use of VR methods in gait control and rehabilitation

Agency in Walking Humans Sensorimotor & [and] Cognitive Contributions to Bodily Self-Consciousness

Acting in our environment and experiencing ourselves as conscious agents are fundamental aspects of human selfhood. While large advances have been made with respect to understanding human sensorimotor control from an engineering approach, knowledge about its interaction with cognition and the conscious experience of movement, i.e. the sense of agency, is still speculative. In this thesis I have investigated these relationships by implementing a Virtual Reality platform, which allowed me to adapt agency paradigms previously limited to movements of individual body-parts to continuous full-body movements, i.e. locomotion. In a series of behavioural studies I investigated how a) spatial and b) temporal sensorimotor mismatches between participants' veridical gait-movements and their life-size visual feedback affected agency and gait. Our results illustrate that humans monitor the details of their movements and their location in space with surprisingly low accuracy. Participants did not become aware of sensorimotor mismatches below 15° and temporal mismatches of 210 ms, even though they automatically adapted their movements. These data confirm that gait and gait agency are distinct brain processes, that these can further be separated by taxing cognitive resources in dual task paradigms, and that they are comparable to agency mechanisms that have been described for upper limb movements. Together, these studies help to investigate sensorimotor components of selfhood that are of scientific, clinical, and legal relevance

Tactile spatial discrimination on the torso using vibrotactile and force stimulation

There is a steadily growing number of mobile communication systems that provide spatially encoded tactile information to the humans’ torso. However, the increased use of such hands-off displays is currently not matched with or supported by systematic perceptual characterization of tactile spatial discrimination on the torso. Furthermore, there are currently no data testing spatial discrimination for dynamic force stimuli applied to the torso. In the present study, we measured tactile point localization (LOC) and tactile direction discrimination (DIR) on the thoracic spine using two unisex torso-worn tactile vests realized with arrays of 3 × 3 vibrotactile or force feedback actuators. We aimed to, first, evaluate and compare the spatial discrimination of vibrotactile and force stimulations on the thoracic spine and, second, to investigate the relationship between the LOC and DIR results across stimulations. Thirty-four healthy participants performed both tasks with both vests. Tactile accuracies for vibrotactile and force stimulations were 60.7% and 54.6% for the LOC task; 71.0% and 67.7% for the DIR task, respectively. Performance correlated positively with both stimulations, although accuracies were higher for the vibrotactile than for the force stimulation across tasks, arguably due to specific properties of vibrotactile stimulations. We observed comparable directional anisotropies in the LOC results for both stimulations; however, anisotropies in the DIR task were only observed with vibrotactile stimulations. We discuss our findings with respect to tactile perception research as well as their implications for the design of high-resolution torso-mounted tactile displays for spatial cueing

Sensorimotor conflicts induce somatic passivity and louden quiet voices in healthy listeners

International audienc

Results Overview.

<p>Walking trajectories were not significantly impacted by the cognitive load and clearly dependent on the introduced angular deviations in both experimental conditions. The main effect of Task on maximum trajectory deviations is due to the fact that the timing of the trials is integrated in these calculations. Walking time (WT), i.e. velocity was significantly affected in the DT condition as participants systematically slowed down. Motor awareness strongly depended on the angular deviations and, in trials around the perceptual threshold, significantly declined in the DT condition.</p><p>mean over deviated trials only;</p><p>Motor Awareness significantly affected by the Dual Task for angular deviations of 10° and 15°.</p><p>(* p<.05, ** p<.01, *** p<.001).</p

Cogno-Vest: A Torso-Worn, Force Display to Experimentally Induce Specific Hallucinations and Related Bodily Sensations

Recent advances in virtual reality and robotic technologies have allowed researchers to explore the mechanisms underlying bodily aspects of self-consciousness which are largely attributed to the multisensory and sensorimotor processing of bodily signals (bodily self-consciousness, BSC). One key contribution to BSC, that is currently poorly addressed due to the lack of a wearable solution, concerns realistic collision sensations on the torso. Here, we introduce and validate a proof-of-concept prototype of torso-worn force display, the Cogno-vest, that provides mechanical touch on the user s back in a sensorimotor perception experiment. In a first empirical study, we characterized human finger poking (N=28). In order to match these poking characteristics and meet the wearability criteria, we used bi-directional, push-pull solenoids as a force actuator in the Cogno-vest. Subsequently, and based on an iterative design procedure, a body-conforming, unisex, torso-worn force display was prototyped. Finally, we conducted a behavioral study that investigated BSC in 25 healthy participants by introducing conflicting sensorimotor signals between their hand and torso (back). Using the final reiteration of the Cogno-vest we successfully replicated previous findings on illusory states of BSC, characterized by presence hallucinations (PH) and passivity symptoms, and achieved higher illusion ratings compared to static conditions used in prior studies

Motor Performance Overview.

<p><b>A</b> Motor Compensation– Participants consistently compensated for the introduced angular deviation as MP monotonously increased with the deviation. The secondary task had no effect on this compensation, even in trials corresponding to the highest perceptual uncertainty (10° and 15°). <b>B </b><b>Time to Target</b> – Participants were significantly slower in the dual task condition than in the single task condition. Independent of cognitive loading participants were significantly faster in the 0° control trials. <b>C </b><b>Average Velocity Profile.</b> The velocity profile shown here is averaged across all trials and participants. Participants slowed down significantly as a result of the secondary cognitive task, articulated serial-7 subtraction. We did not observe an initial freezing-like behaviour as there was no change in the time participants took to cross the first 30 cm of each trial, as indicated by the dotted black lines. Instead, walking velocity was lower over the entire trial. Error bars are standard error of the mean (SEM).</p