Continuous Semi-autonomous Prosthesis Control Using a Depth Sensor on the Hand.

Modern myoelectric prostheses can perform multiple functions (e.g., several grasp types and wrist rotation) but their intuitive control by the user is still an open challenge. It has been recently demonstrated that semi-autonomous control can allow the subjects to operate complex prostheses effectively; however, this approach often requires placing sensors on the user. The present study proposes a system for semi-autonomous control of a myoelectric prosthesis that requires a single depth sensor placed on the dorsal side of the hand. The system automatically pre-shapes the hand (grasp type, size, and wrist rotation) and allows the user to grasp objects of different shapes, sizes and orientations, placed individually or within cluttered scenes. The system "reacts" to the side from which the object is approached, and enables the user to target not only the whole object but also an object part. Another unique aspect of the system is that it relies on online interaction between the user and the prosthesis; the system reacts continuously on the targets that are in its focus, while the user interprets the movement of the prosthesis to adjust aiming. Experimental assessment was conducted in ten able-bodied participants to evaluate the feasibility and the impact of training on prosthesis-user interaction. The subjects used the system to grasp a set of objects individually (Phase I) and in cluttered scenarios (Phase II), while the time to accomplish the task (TAT) was used as the performance metric. In both phases, the TAT improved significantly across blocks. Some targets (objects and/or their parts) were more challenging, requiring thus significantly more time to handle, but all objects and scenes were successfully accomplished by all subjects. The assessment therefore demonstrated that the system is indeed robust and effective, and that the subjects could successfully learn how to aim with the system after a brief training. This is an important step toward the development of a self-contained semi-autonomous system convenient for clinical applications.

A software for testing and training visuo-motor coordination for upper limb control.

BACKGROUND: Developing methods to accelerate improvements in motor function are welcomed in clinical practice. Therefore, the aim of this study is to describe changes in brain activity related to the execution of motor tasks implemented on a software - the NeuroMaze - developed specifically to stimulate speed-accuracy tradeoff. NEW METHOD: The NeuroMaze was tested in eleven young and healthy individuals in a single experimental session. The tasks consisted in moving a square appearing on the monitor by holding and dragging it with a mouse across paths of different widths (wide [2 cm] vs intermediate [1.5 cm] vs narrow [1 cm] widths). The mouse cursor speed and scalp electroencephalography (EEG) from the frontal, somatosensory and motor areas were recorded. RESULTS: The mouse speed is reduced by 15 ±â€¯6% and 48 ±â€¯7% from the wide to the intermediate and narrow paths respectively (p < 0.005). Moreover, there was a greater beta EEG relative power in the narrow path in the frontal area of the brain when compared to the wide path (p < 0.05). Similarly, the narrow path reduced the gamma EEG relative power in motor/sensorimotor areas when compared to the wide path (p < 0.05). COMPARISON WITH EXISTING METHODS: The NeuroMaze is introduced as a method to elicit speed-accuracy tradeoff, and the authors are not aware of specific methods to establish fair comparisons. CONCLUSION: The NeuroMaze creates conditions to stimulate brain areas related to motor planning, sensory feedback and motor execution using speed-accuracy tradeoff contexts. Therefore, the NeuroMaze may induce adaptations in patients undergoing upper limb rehabilitation.

Validation of subject-specific musculoskeletal models using the anatomical reachable 3-D workspace.

A novel metric for the validation of musculoskeletal models is proposed, the reachable 3-D workspace (RWS). This new metric was used to compare a generic model scaled in a standard manner to a more subject-specific model. An experimental protocol for assessing the RWS was performed by ten participants for four distinct hand-payload cases. In addition, isometric individual strength measurements were collected for 12 different directions. The strength of subject-specific musculoskeletal models was then computed using the following assumptions: (1) standard routines including the length-mass-fat (LMF) scaling law; (2) the isometric strengths of the muscle elements were optimized to the individual strength measurements using joint strength factors (JSF). The RWS of each participant was subsequently estimated from each of the scaling approaches, LMF and JSF, for the four load cases. The experimental RWS showed that the volume and shape decreased with increasing hand-payload for every participant. The lateral and frontal far-from-torso aspects of the RWS were reduced the most. These trends were reproduced by both strength scaling approaches, but the LMF-scaled models were not able to track the overall RWS volume decrease with increasing payload, since they proved to be weaker than the participants. On the other hand, the optimised JSF subject-specific models performed better on the prediction of the RWS for all payload cases across participants. The RWS can potentially be further used as a subject-specific musculoskeletal model validation, enabling quantification of the volume and shape differences between experimentally and model-predicted RWSs.

The reachable 3-D workspace volume is a measure of payload and body-mass-index: A quasi-static kinetic assessment.

An experimental protocol with five tasks is proposed for a low-cost empirical assessment of the reachable 3-D workspace (RWS), including both close-to-torso and far-from-torso regions. Ten participants repeated the protocol for four distinct hand payloads. The RWS expressed as a point cloud and its non-convex alpha-shape were obtained for each case. Moreover, individual strength surrogates for glenohumeral flexion and abduction, and elbow flexion were collected using a dynamometer. The RWS volume was statistically modelled using payload, body-mass-index and the strength surrogates as predictors. For increasing payload, a significant (r = -0.736,p < 0.001) decrease in RWS volume was found for distinct payload cases across all subjects. The only significant predictors found for the RWS volume were normalized payload (F = 73.740,p < 0.001) and body-mass-index (F = 11.008,p = 0.003). No significant interactions were found. The consequent regression model (F(2,27) = 41.11, p < 0.001, Radj2 = 0.7345) explained around 73% of the variation in the data. The RWS volume is a function of payload and body-mass-index.

The cognitive complexity of concurrent cognitive-motor tasks reveals age-related deficits in motor performance.

Aging reduces cognitive functions, and such impairments have implications in mental and motor performance. Cognitive function has been recently linked to the risk of falls in older adults. Physical activities have been used to attenuate the declines in cognitive functions and reduce fall incidence, but little is known whether a physically active lifestyle can maintain physical performance under cognitively demanding conditions. The aim of this study was to verify whether physically active older adults present similar performance deficits during upper limb response time and precision stepping walking tasks when compared to younger adults. Both upper limb and walking tasks involved simple and complex cognitive demands through decision-making. For both tasks, decision-making was assessed by including a distracting factor to the execution. The results showed that older adults were substantially slower than younger individuals in the response time tasks involving decision-making. Similarly, older adults walked slower and extended the double support periods when precision stepping involved decision-making. These results suggest that physically active older adults present greater influence of cognitive demanding contexts to perform a motor task when compared to younger adults. These results underpin the need to develop interventions combining cognitive and motor contexts.