Adam Wilson

A novel approach to surface electromyography: an exploratory study of electrode-pair selection based on signal characteristics

A 3 × 4 electrode array was placed over each of seven muscles and surface electromyography (sEMG) data were collected during isometric contractions. For each array, nine bipolar electrode pairs were formed off-line and sEMG parameters were calculated and evaluated based on repeatability across trials and comparison to an anatomically placed electrode pair. The use of time-domain parameters for the selection of an electrode pair from within a grid-like array may improve upon existing electrode placement methodologies.

A Bus-Based Smart Myoelectric Electrode/Amplifier—System Requirements

The evaluation of a bus-based smart myoelectric electrode/amplifier is described that is to be used in conjunction with a multi-function prosthetic hand controller. The smart electrode/amplifier was designed to meet power consumption and size specifications of commercially available myoelectric amplifiers used for prosthetic control applications while providing a number of additional features. This paper investigates the electrode/amplifier requirements for a pattern classifier system and compares them to those currently accepted within a clinical setting. System testing and evaluation was performed with both normally limbed subjects and traumatic amputees.

A bus-based smart myoelectric electrode/amplifier

The design of a bus-based smart myoelectric electrode/amplifier is described that is be used in conjunction with a multi-function prosthetic hand controller. This system incorporates several different control strategies including pattern classification of EMG to control a three axis hand (The UNB Hand) that can perform six basic grip patterns. The smart electrode/amplifier was designed to meet power consumption and size specifications of commercially available myoelectric amplifiers used for prosthetic control applications while providing a host of additional features. These features include a CAN bus communication protocol to alleviate wiring complexity, software programmable gain, distributed signal processing and electrode lift detection. In addition, this paper also compares the differences in requirements between a myoelectric electrode/amplifier used in a pattern classifier system to that used in a clinical setting. System testing and evaluation with normally limbed subjects and traumatic amputees are presented.

Crossmodal congruency effect scores decrease with repeat test exposure

The incorporation of feedback into a person’s body schema is well established. The crossmodal congruency effect (CCE) task is used to objectively quantify incorporation without being susceptible to experimenter biases. This visual-tactile interference task is used to calculate the CCE score as a difference in response time for incongruent and congruent trials. Here we show that this metric is susceptible to a learning effect that causes attenuation of the CCE score due to repeated task exposure sessions. We demonstrate that this learning effect is persistent, even after a 6 month hiatus in testing. Two mitigation strategies are proposed: 1. Only use CCE scores that are taken after learning has stabilized, or 2. Use a modified CCE protocol that decreases the task exposure time. We show that the modified and shortened CCE protocol, which may be required to meet time or logistical constraints in laboratory or clinical settings, reduced the impact of the learning effect on CCE results. Importantly, the CCE scores from the modified protocol were not significantly more variable than results obtained with the original protocol. This study highlights the importance of considering exposure time to the CCE task when designing experiments and suggests two mitigation strategies to improve the utility of this psychophysical assessment.The incorporation of a tool into a person9s body representation is well established. Quantitative measures play an important role in assessing tool incorporation levels for tool use paradigms. The crossmodal congruency effect (CCE) is used to quantify tool incorporation without being susceptible to experimenter biases. The crossmodal congruency task is a visual-tactile interference task that is used to calculate the CCE score as a difference in response time for incongruent and congruent trials. Here we show that this metric is susceptible to a learning effect that causes attenuation of the CCE score due to repeated task exposure sessions. This study investigated the conditions under which CCE scores attenuated due to task overexposure and tested if a modified version of the crossmodal congruency task could reduce the learning effect. Our work also sought to examine if the attenuated CCE scores returned to baseline values after a period of time. Thirty subjects were tested up to a maximum of ten times and four of these subjects were retested after a four month delay period. We show that CCE score reduced as early as the second exposure with a 14.5% drop between first and second exposures (p=0.027). Importantly, we found evidence that a modified version of the crossmodal congruency task, in which each exposure was reduced from eight to four test blocks, reduced the drop between first and second exposure from an average of 14.5% to 6.5% without significantly increasing variability of the measurement. Additionally, we found that three out of four subjects that were retested after a four month period returned to near-baseline CCE scores. This study highlights the importance of limiting exposure to the crossmodal congruency task, and proposes a modified approach to improve the use of this psychophysical assessment in the future.

Assessing the quality of supplementary sensory feedback using the crossmodal congruency task

Advanced neural interfaces show promise in making prosthetic limbs more biomimetic and ultimately more intuitive and useful for patients. However, approaches to assess these emerging technologies are limited in scope and the insight they provide. When outfitting a prosthesis with a feedback system, such as a peripheral nerve interface, it would be helpful to quantify its physiological correspondence, i.e. how well the prosthesis feedback mimics the perceived feedback in an intact limb. Here we present an approach to quantify this aspect of feedback quality using the crossmodal congruency effect (CCE) task. We show that CCE scores are sensitive to feedback modality, an important characteristic for assessment purposes, but are confounded by the spatial separation between the expected and perceived location of a stimulus. Using data collected from 60 able-bodied participants trained to control a bypass prosthesis, we present a model that results in adjusted-CCE scores that are unaffected by percept misalignment which may result from imprecise neural stimulation. The adjusted-CCE score serves as a proxy for a feedback modality’s physiological correspondence or ‘naturalness’. This quantification approach gives researchers a tool to assess an aspect of emerging augmented feedback systems that is not measurable with current motor assessments.

Author Correction: Assessing the quality of supplementary sensory feedback using the crossmodal congruency task

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Evaluation of a toolkit for standardizing clinical measures of muscle tone

OBJECTIVE To evaluate a new portable toolkit for quantifying upper and lower extremity muscle tone in patients with upper motor neuron syndrome (UMNS). APPROACH Cross-sectional, multi-site, observational trial to test and validate a new technology. SETTING Neurorehabilitation clinics at tertiary care hospitals. PARTICIPANTS Four cohorts UMNS patient, >6 mo post acquired brain injury, spinal cord injury, multiple sclerosis and cerebral palsy, and a sample of healthy age-matched adult controls. MEASURES Strength: grip, elbow flexor and extensor, and knee extensor; range of motion (ROM): passive ROM (contracture) and passive-active ROM (paresis); objective spasticity: stretch-reflex test for elbow, and pendulum test for knee; subjective spasticity: modified Ashworth scale scores for elbow and knee flexors and extensors. RESULTS Measures were acquired for 103 patients from three rehabilitation clinics. Results for patient cohorts were consistent with the literature. Grip strength correlated significantly with elbow muscle strength and all patient populations were significantly weaker in upper- and lower-extremity compared to controls. Strength and paresis were correlated for elbow and knee but neither correlated with contracture. Elbow spasticity correlated with strength and paresis but not contracture. Knee spasticity correlated with strength, and subjective spasticity correlated with contracture. SIGNIFICANCE The BioTone™ toolkit provided comprehensive objective measures for assessing muscle tone in patients with UMNS. The toolkit could be useful for standardizing outcomes measures in clinical trials and for routine practice.

Analyzing Bus Load Data Using an FPGA and a Microcontroller

In this paper we present the design, implementation, and testing of an evaluation tool for the ongoing development of the Prosthetic Device Communication Protocol (PDCP) which is an open protocol and is featured in the University of New Brunswicks most recent prosthetic limb research project, the UNB Hand System. This prosthetic device utilizes the CAN bus hardware with the PDCP for passing command and data messages between modules within the prosthetic limb system. The PDCP allows abstraction of the underlying bus system and allows different network topologies depending on particular needs. To be able to analyze communication in the CAN layers as well as in the PDCP layer we present our own solutions utilizing an FPGA for CAN bus bandwidth load monitoring and a microcontroller for PDCP monitoring and analysis.