Surface electromyography for speech and swallowing systems: measurement, analysis, and interpretation

Position-independent gesture recognition using sEMG signals via canonical correlation analysis

Gesture recognition based on surface electromyogram (sEMG) signals has drawn significant attention and obtained satisfactory achievement in the field of human-computer interaction. However, the same gesture performed with different arm positions tends not to generate the same sEMG signals. Traditional solutions can be divided into two types. One type treats the same gesture with different arm positions as the same type, leading to a relatively low classification rate. The other type adopts a gesture classifier followed by the position classifier, which will achieve a satisfactory classification accuracy but at the expenses of high training burdens. To address these issues, we propose a novel framework to explore the intrinsic position independent (PI) characteristics of sEMG signals generated from the same gesture with different arm positions by canonical correlation analysis (CCA), termed as PICCA. In this framework, with the bridge link of the predefined expert set, both the training set and the testing set can be mapped into a unified-style with CCA, and hence, the classification accuracy can be improved in both user-dependent and user-independent manners. Experimental results on 13 gestures with 3 arm positions indicate that the proposed PICCA can achieve higher classification rates than those without CCA (with 28.52% and 44.19% promotions during user-dependent and user-independent manners respectively) while maintaining acceptable training burdens. These improvements will facilitate the practical implementation of myoelectric interfaces.

Prediction of Optimal Facial Electromyographic Sensor Configurations for Human-Machine Interface Control

Surface electromyography (sEMG) is a promising computer access method for individuals with motor impairments. However, optimal sensor placement is a tedious task requiring trial-and-error by an expert, particularly when recording from facial musculature likely to be spared in individuals with neurological impairments. We sought to reduce the sEMG sensor configuration complexity by using quantitative signal features extracted from a short calibration task to predict human-machine interface (HMI) performance. A cursor control system allowed individuals to activate specific sEMG-targeted muscles to control an onscreen cursor and navigate a target selection task. The task was repeated for a range of sensor configurations to elicit a range of signal qualities. Signal features were extracted from the calibration of each configuration and examined via a principle component factor analysis in order to predict the HMI performance during subsequent tasks. Feature components most influenced by the energy and the complexity of the EMG signal and muscle activity between the sensors were significantly predictive of the HMI performance. However, configuration order had a greater effect on performance than the configurations, suggesting that non-experts can place sEMG sensors in the vicinity of usable muscle sites for computer access and healthy individuals will learn to efficiently control the HMI system.

Individuality of masticatory performance and of masticatory muscle temporal parameters

OBJECTIVE

Mammalian mastication serves to improve intra-oral food reduction. Insufficient food reduction creates potential swallowing problems, whereas over-reduction may accelerate tooth wear and increase feeding time. Either extreme has consequences. The study's objectives were: (1) to study the relationship between food reduction, number of chews in a sequence, and chewing rate, (2) to study how controlling the number of chews and chewing rate variability affects food reduction, and (3) to assess how dentoskeletal morphological and electromyographical (EMG) characteristics impact food reduction.

DESIGN

Twenty-three healthy, fully-dentate adults chewed a standardized test food under three conditions: (1) no control, (2) number of chews controlled, and (3) number of chews and chewing rate controlled. EMG activity was sampled from masseter and temporalis muscles bilaterally. Demographic, occlusal contact area in maximum intercuspation, and cephalometric data were obtained.

RESULTS

In uncontrolled conditions, food reduction and bout duration varied more than expected across subjects. Subjects with poor reduction under controlled conditions were those with poor reduction under uncontrolled conditions. Only occlusal contact area correlated with chewing performance under uncontrolled conditions. Chewing cycle duration, EMG burst duration, and EMG peak onset latency increased when the number of chews was restricted. EMG amplitude, a surrogate for bite force, increased in tasks controlling the number of chews and chewing rate. Chewing rate variability was difficult to diminish below individual-specific levels.

CONCLUSIONS

Results: provided evidence that bite force, chewing rate, chewing performance and chewing bout duration reflected individual preferences. Future work will determine whether similar findings occur among other mammals.

A Novel Feature Optimization for Wearable Human-Computer Interfaces Using Surface Electromyography Sensors

The novel human-computer interface (HCI) using bioelectrical signals as input is a valuable tool to improve the lives of people with disabilities. In this paper, surface electromyography (sEMG) signals induced by four classes of wrist movements were acquired from four sites on the lower arm with our designed system. Forty-two features were extracted from the time, frequency and time-frequency domains. Optimal channels were determined from single-channel classification performance rank. The optimal-feature selection was according to a modified entropy criteria (EC) and Fisher discrimination (FD) criteria. The feature selection results were evaluated by four different classifiers, and compared with other conventional feature subsets. In online tests, the wearable system acquired real-time sEMG signals. The selected features and trained classifier model were used to control a telecar through four different paradigms in a designed environment with simple obstacles. Performance was evaluated based on travel time (TT) and recognition rate (RR). The results of hardware evaluation verified the feasibility of our acquisition systems, and ensured signal quality. Single-channel analysis results indicated that the channel located on the extensor carpi ulnaris (ECU) performed best with mean classification accuracy of 97.45% for all movement’s pairs. Channels placed on ECU and the extensor carpi radialis (ECR) were selected according to the accuracy rank. Experimental results showed that the proposed FD method was better than other feature selection methods and single-type features. The combination of FD and random forest (RF) performed best in offline analysis, with 96.77% multi-class RR. Online results illustrated that the state-machine paradigm with a 125 ms window had the highest maneuverability and was closest to real-life control. Subjects could accomplish online sessions by three sEMG-based paradigms, with average times of 46.02, 49.06 and 48.08 s, respectively. These experiments validate the feasibility of proposed real-time wearable HCI system and algorithms, providing a potential assistive device interface for persons with disabilities.

Voz cantada y Electromiografía de Superficie: Un estudio comparativo de la actividad muscular en cantantes formados y no formados

En los últimos años ha habido un incremento del uso de la Electromiografía de Superficie en logopedia, lo que se evidencia en el número creciente de publicaciones en este área en revistas científicas. Este instrumento permite presentar de forma objetiva y precisa la actividad mioeléctrica en tiempo real, es no invasiva y se percibe de fácil aplicación. El objetivo de este trabajo es comparar la actividad mioeléctrica de los músculos maseteros, suprahioideos y esternoicleidomastoideos de cantantes con y sin entrenamiento vocal reglado a través de la Electromiografía de Superficie durante la realización de un fonetograma. La muestra estuvo conformada por 12 sopranos con edades entre 19 y 29 años, 6 con formación reglada en canto y 6 sin formación. Previo a la recogida de datos se calibró el sistema de análisis acústico a través de un calibrador y un dosímetro. Las muestras se recogieron en un gabinete insonorizado, previo consentimiento informado de los participantes. Se fijaron los electrodos en cada uno de los músculos, tanto derechos como izquierdos y se llevó a cabo el protocolo de registro de la actividad mioeléctrica. Se observaron diferencias estadísticamente significativas a nivel de los músculos esternocleidomastoideos, siendo mayor su actividad en los cantantes formados respecto a los no formados. No se obtuvieron diferencias significativas en los otros músculos estudiados. Puede concluirse que los cantantes con formación reglada presentan mayor actividad a nivel de músculos esternocleidomastoideos respecto a los no formados. Es necesario seguir investigando con muestras más amplias para llegar a resultados más concluyentes.

Submental Muscle Activation During Lingual Tasks in Healthy Adults

OBJECTIVE

Lingual strengthening exercises are established to improve lingual function, thereby oral swallowing. This study measured submental muscle activation during maximum isometric pressure (MIP) lingual tasks in healthy adults, tasks that are or can be adopted in lingual strengthening exercises. In addition, the effects of age and gender on submental muscle activation are examined.

METHOD

Forty-nine participants between the ages of 18 to 35 years and greater than 60 years were included in the study. Participants completed trials of intraoral MIP lingual elevation, protrusion, and depression, during which submental muscle activation was measured using surface electromyography (sEMG). Peak amplitude measures were normalized and log transformed, following which a three-way ANOVA was performed.

RESULTS

Peak amplitudes of submental muscle activation were highest during lingual MIP protrusion, followed by lingual depression, and were least during lingual elevation. No significant differences in peak amplitudes were observed between older and younger adults, but higher peak amplitudes were recorded in women.

CONCLUSION

The differential effects of lingual task, age, and gender on peak submental muscle activation are examined. The potential impact of incorporating tasks adopted in this study in lingual strengthening exercises to improve oral and pharyngeal swallowing is discussed.

Polar-phase indices of perioral muscle reciprocity during syllable production in Parkinson's disease

PURPOSE

This research characterised perioral muscle reciprocity and amplitude ratio in lower lip during bilabial syllable production [pa] at three rates to understand the neuromotor dynamics and scaling of motor speech patterns in individuals with Parkinson's disease (PD).

METHOD

Electromyographic (EMG) signals of the orbicularis oris superior [OOS], orbicularis oris inferior [OOI] and depressor labii inferioris [DLI] were recorded during syllable production and expressed as polar-phase notations.

RESULT

PD participants exhibited the general features of reciprocity between OOS, OOI and DLI muscles as reflected in the EMG during syllable production. The control group showed significantly higher integrated EMG amplitude ratio in the DLI:OOS muscle pairs than PD participants. No speech rate effects were found in EMG muscle reciprocity and amplitude magnitude across all muscle pairs.

CONCLUSION

Similar patterns of muscle reciprocity in PD and controls suggest that corticomotoneuronal output to the facial nucleus and respective perioral muscles is relatively well-preserved in our cohort of mild idiopathic PD participants. Reduction of EMG amplitude ratio among PD participants is consistent with the putative reduction in the thalamocortical activation characteristic of this disease which limits motor cortex drive from generating appropriate commands which contributes to bradykinesia and hypokinesia of the orofacial mechanism.

Evaluation of normal swallowing functions by using dynamic high-density surface electromyography maps

BACKGROUND

Swallowing is a continuous process with substantive interdependencies among different muscles, and it plays a significant role in our daily life. The aim of this study was to propose a novel technique based on high-density surface electromyography (HD sEMG) for the evaluation of normal swallowing functions.

METHODS

A total of 96 electrodes were placed on the front neck to acquire myoelectric signals from 12 healthy subjects while they were performing different swallowing tasks. HD sEMG energy maps were constructed based on the root mean square values to visualize muscular activities during swallowing. The effects of different volumes, viscosities, and head postures on the normal swallowing process were systemically investigated by using the energy maps.

RESULTS

The results showed that the HD sEMG energy maps could provide detailed spatial and temporal properties of the muscle electrical activity, and visualize the muscle contractions that closely related to the swallowing function. The energy maps also showed that the swallowing time and effort was also explicitly affected by the volume and viscosity of the bolus. The concentration of the muscular activities shifted to the opposite side when the subjects turned their head to either side.

CONCLUSIONS

The proposed method could provide an alternative method to physiologically evaluate the dynamic characteristics of normal swallowing and had the advantage of providing a full picture of how different muscle activities cooperate in time and location. The findings from this study suggested that the HD sEMG technique might be a useful tool for fast screening and objective assessment of swallowing disorders or dysphagia.

Validity and Reliability of Surface Electromyography in the Assessment of Primary Muscle Tension Dysphonia

OBJECTIVE

The study aims to evaluate the reliability and the discriminative validity of surface electromyography (sEMG) in the assessment of patients with primary muscle tension dysphonia (MTD).

STUDY DESIGN

The study design is cross-sectional.

METHODS

Fifteen patients with primary MTD (mean age: 34.07 ± 10.99 years) and 15 healthy volunteers (mean age: 34.53 ± 10.63 years) were included. All participants underwent evaluation of sEMG to record the electrical activity of the thyrohyoid and cricothyroid muscles. The outcome measures were the root mean square (RMS), activity peak, duration, and time to the peak activity, which were obtained during /a/ and /i/ prolongation for test-retest reliability.

RESULTS

The test-retest reliability was good to excellent for the RMS and peak activity measures (intraclass correlation coefficient [agreement] [ICC_agreement] = 0.49-0.98). The reliability for the activity duration was poor to excellent (ICC_agreement = 0.19-0.9). Poor test-retest reliability was found for the time to peak measure (ICC_agreement = 0.15-0.37). The standard error of measurement for all sEMG measures was between 0.41 and 2.05. The smallest detectable change (SDC) was calculated between 1.13 and 5.66. The highest SDC values were obtained for the peak and the lowest SDCs were documented for the duration (5.66 and 1.13, respectively). All sEMG measures were not able to discriminate between the MTD patients and healthy subjects (P > 0.05).

CONCLUSIONS

The sEMG is a reliable tool to measure the RMS, the peak activity, and the activity duration in primary MTD. However, it is not able to discriminate the patients with primary MTD from healthy subjects.

Soft Electronics Enabled Ergonomic Human-Computer Interaction for Swallowing Training

We introduce a skin-friendly electronic system that enables human-computer interaction (HCI) for swallowing training in dysphagia rehabilitation. For an ergonomic HCI, we utilize a soft, highly compliant ("skin-like") electrode, which addresses critical issues of an existing rigid and planar electrode combined with a problematic conductive electrolyte and adhesive pad. The skin-like electrode offers a highly conformal, user-comfortable interaction with the skin for long-term wearable, high-fidelity recording of swallowing electromyograms on the chin. Mechanics modeling and experimental quantification captures the ultra-elastic mechanical characteristics of an open mesh microstructured sensor, conjugated with an elastomeric membrane. Systematic in vivo studies investigate the functionality of the soft electronics for HCI-enabled swallowing training, which includes the application of a biofeedback system to detect swallowing behavior. The collection of results demonstrates clinical feasibility of the ergonomic electronics in HCI-driven rehabilitation for patients with swallowing disorders.

Reliability of quadriceps surface electromyography measurements is improved by two vs. single site recordings

Purpose

The reliability of surface electromyography (sEMG) is typically modest even with rigorous methods, and therefore further improvements in sEMG reliability are desirable. This study compared the between-session reliability (both within participant absolute reliability and between-participant relative reliability) of sEMG amplitude from single vs. average of two distinct recording sites, for individual muscle (IM) and whole quadriceps (WQ) measures during voluntary and evoked contractions.

Methods

Healthy males (n = 20) performed unilateral isometric knee extension contractions: voluntary maximum and submaximum (60%), as well as evoked twitch contractions on two separate days. sEMG was recorded from two distinct sites on each superficial quadriceps muscle.

Results

Averaging two recording sites vs. using single site measures improved reliability for IM and WQ measurements during voluntary (16–26% reduction in within-participant coefficient of variation, CV_W) and evoked contractions (40–56% reduction in CV_W).

Conclusions

For sEMG measurements from large muscles, averaging the recording of two distinct sites is recommended as it improves within-participant reliability. This improved sensitivity has application to clinical and research measurement of sEMG amplitude.

Identification of the most significant electrode positions in electromyographic evaluation of swallowing-related movements in humans

Surface electromyography (sEMG) is a well-established procedure for recording swallowing-related muscle activities. Because the use of a large number of sEMG channels is time consuming and technically sophisticated, the aim of this study was to identify the most significant electrode positions associated with oropharyngeal swallowing activities. Healthy subjects (N = 16) were tested with a total of 42 channels placed in M. masseter, M. orbicularis oris, submental and paralaryngeal regions. Each test subject swallowed 10 ml of water five times. After having identified 16 optimal electrode positions, that is, positions with the strongest signals quantified by the highest integral values, differences to 26 other ones were determined by a Mann-Whitney U test. Kruskal-Wallis H test was utilized for the analysis of differences between single subjects, subject subgroups, and single electrode positions. Factors associated with sEMG signals were examined in a linear regression. Sixteen electrode positions were chosen by a simple ranking of integral values. These positions delivered significantly higher signals than the other 26 positions. Differences between single electrode positions and between test subjects were also significant. Sixteen most significant positions were identified which represent swallowing-related muscle potentials in healthy subjects.

Electromyography and Mechanomyography Signals During Swallowing in Healthy Adults and Head and Neck Cancer Survivors

Surface electromyography (sEMG) is used as an adjuvant to dysphagia therapy to demonstrate the activity of submental muscles during swallowing exercises. Mechanomyography (MMG) has been suggested as a potential superior alternative to sEMG; however, this advantage is not confirmed for signal acquired from submental muscles. This study compared the signal-to-noise ratio (SNR) obtained from sEMG and MMG sensors during swallowing tasks, in healthy participants and those with a history of head and neck cancer (HNC), a population with altered anatomy and a high incidence of dysphagia. Twenty-two healthy adults and 10 adults with a history of HNC participated in this study. sEMG and MMG signals were acquired during dry, thin liquid, effortful, and Mendelsohn maneuver swallows. SNR was compared between the two sensors using repeated measures ANOVAs and subsequent planned pairwise comparisons. Test-retest measures were collected on 20 % of participants. In healthy participants, MMG SNR was higher than that of sEMG for dry [t(21) = -3.02, p = 0.007] and thin liquid swallows [t(21) = -4.24, p < 0.001]. Although a significant difference for sensor was found in HNC participants F(1,9) = 5.54, p = 0.043, planned pairwise comparisons by task revealed no statistically significant difference between the two sensors. sEMG also showed much better test-retest reliability than MMG. Biofeedback provided as an adjuvant to dysphagia therapy in patients with HNC should employ sEMG technology, as this sensor type yielded better SNR and overall test-retest reliability. Poor MMG test-retest reliability was noted in both healthy and HNC participants and may have been related to differences in sensor application.

Effects of tongue pressing effortful swallow in older healthy individuals

INTRODUCTION

The risk of swallowing disorders is increased for older individuals due to weak tongue and pharyngeal muscle strength. This study was appraised the value of a preventative approach by developing the tongue pressing effortful swallow (TPES) applied using a home-based and self-administered procedure. The TPES was developed by combining two swallowing exercises: tongue strengthening exercise and the effortful swallow. The purpose of this study was to examine the effects of the TPES on maximum tongue pressure and peak amplitude of submental muscle activity in older individuals.

MATERIAL AND METHODS

27 older individuals (mean 73 years) performed a 4-week TPES. The exercise program was adapted to a home-based and self-administered procedure. The maximum tongue pressure was measured by the Iowa Oral Performance Instrument and peak amplitude of submental muscle activity by surface electromyography (sEMG). Statistical comparisons were made by a matched pairs t-test (p<0.05).

RESULTS

The results of this study showed that the TPES had statistically significant and positive effects on increasing maximum tongue pressure, but the peak amplitude of the submental sEMG did not differ between before and after exercises.

CONCLUSIONS

The TPES had a positive impact in older individuals. The TPES, a combining exercise, was possible because two exercises had common physiological events. The TPES was a more innovative and efficient approach than the tongue strengthening exercise alone. In addition, older individuals were able to perform the swallowing exercise at home and by themselves with little assistance. Future research needs to refine the TPES and apply it to patients with dysphagia.

Effect of age on human-computer-interface control via neck electromyography

The purpose of this study was to determine the effect of age on visuomotor tracking using submental and anterior neck surface electromyography (sEMG) to assess feasibility of computer control via neck musculature, which allows people with little remaining motor function to interact with computers. Thirty-two healthy adults participated: sixteen younger adults aged 18 - 29 years and sixteen older adults aged 69 - 85 years. Participants modulated sEMG to achieve targets presented at different amplitudes using real-time visual feedback. Root-mean-squared (RMS) error was used to quantify tracking performance. RMS error was increased for older adults relative to younger adults. Older adults demonstrated more RMS error than younger adults as a function of increasing target amplitude. The differential effects of age found on static tracking performance in anterior neck musculature suggest more difficult translation of human-computer-interfaces controlled using anterior neck musculature for static tasks to older populations.

The Relationship Between Submental Surface Electromyography and Hyo-Laryngeal Kinematic Measures of Mendelsohn Maneuver Duration

PURPOSE

The Mendelsohn Maneuver (MM) is a commonly prescribed technique that is taught to individuals with dysphagia to improve swallowing ability. Due to cost and safety concerns associated with videofluoroscopy (VFS) use, submental surface electromyography (ssEMG) is commonly used in place of VFS to train the MM in clinical and research settings. However, it is unknown whether ssEMG accurately reflects the prolonged hyo-laryngeal movements required for execution of the MM. The primary goal of this study was to examine the relationship among ssEMG duration, duration of laryngeal vestibule closure, and duration of maximum hyoid elevation during MM performance.

METHOD

Participants included healthy adults and patients with dysphagia due to stroke. All performed the MM during synchronous ssEMG and VFS recording.

RESULTS

Significant correlations between ssEMG duration and VFS measures of hyo-laryngeal kinematic durations during MM performance ranged from very weak to moderate. None of the correlations in the group of stroke patients reached statistical significance.

CONCLUSION

Clinicians and researchers should consider that the MM involves novel hyo-laryngeal kinematics that may be only moderately represented with ssEMG. Thus, there is a risk that these target therapeutic movements are not consistently being trained.

Detection of Simulated Vocal Dysfunctions Using Complex sEMG Patterns

Symptoms of voice disorder may range from slight hoarseness to complete loss of voice; from modest vocal effort to uncomfortable neck pain. But even minor symptoms may still impact personal and especially professional lives. While early detection and diagnosis can ameliorate that effect, to date, we are still largely missing reliable and valid data to help us better screen for voice disorders. In our previous study, we started to address this gap in research by introducing an ambulatory voice monitoring system using surface electromyography (sEMG) and a robust algorithm (HiGUSSS) for pattern recognition of vocal gestures. Here, we expand on that work by further analyzing a larger set of simulated vocal dysfunctions. Our goal is to demonstrate that such a system has the potential to recognize and detect real vocal dysfunctions from multiple individuals with high accuracy under both intra and intersubject conditions. The proposed system relies on four sEMG channels to simultaneously process various patterns of sEMG activation in the search for maladaptive laryngeal activity that may lead to voice disorders. In the results presented here, our pattern recognition algorithm detected from two to ten different classes of sEMG patterns of muscle activation with an accuracy as high as 99%, depending on the subject and the testing conditions.

The Recline Exercise: Comparisons with the Head Lift Exercise in Healthy Adults

The aim of this investigation was to examine the comparative effectiveness of the new Recline Exercise (RE) and the traditional Head Lift Exercise (Shaker Exercise) on submental muscle activity, tongue strength, and perceived exertion in 40 healthy young adults (mean age = 24.5 years, SD 2.6 years). Both groups participated in a 6-week exercise regimen. Outcome variables evaluated pre- and post-exercise included: duration and peak amplitude of submental muscle activity during swallowing measured via surface electromyography (sEMG); anterior and posterior isometric lingual pressures measured with the Iowa Oral Performance Instrument; and perceived exertion levels measured with the Borg category-ratio scale of perceived exertion. Results indicated no significant pre-post differences within or between groups in swallow duration and peak amplitude. In addition, the RE group demonstrated significant post-treatment increases in anterior and posterior tongue strength [p = 0.009; p < 0.001]; however, these increases were of small magnitude (d = 0.132; d = 0.319). Both groups showed marked improvements in perceived exertion levels [p < 0.001]. Our findings indicate that healthy young adults who perform the RE or the HLE do not have significant swallow duration or amplitude gains, most likely due to the reduced need for such gains in the healthy head/neck musculature for submaximal tasks. Furthermore, the significant lingual strength gains seen with the RE indicate that additional musculature is being engaged during its completion. These results are encouraging; however, future research in older adults and patients with dysphagia with examination of swallowing biomechanics is needed to determine its full potential as a rehabilitative regimen.

Visuomotor control of neck surface electromyography in Parkinson's disease

OBJECTIVE

To compare performance of individuals with Parkinson's disease (PD) and age-matched controls on a visuomotor tracking task controlled via surface electromyography (sEMG).

METHODS

Twenty-seven adults with PD and twenty-four older controls produced dry swallows and completed a visuomotor tracking task utilizing both static and dynamic targets. sEMG was recorded at the anterior neck and submental surface during both tasks.

RESULTS

There was no significant difference in visuomotor tracking ability between cohorts. Post hoc analyses indicated that there was no significant difference between participant groups in the strength or duration of swallows as measured by sEMG but that participants with PD showed a trend for decreased swallow durations at the anterior neck (padj = 0.067) whereas controls showed a trend for increased durations at the anterior neck (padj = 0.112), compared to the submental surface. However, there were no significant correlations between swallowing behavior and visuomotor tracking ability.

CONCLUSION

There were no significant differences in visuomotor tracking performance between individuals with PD and controls. Furthermore, there was no relationship between tracking ability and swallowing behavior. We conclude that sEMG-mediated biofeedback may have limited promise as a tool for treating PD-related dysphagia.

Discrete Versus Continuous Mapping of Facial Electromyography for Human-Machine Interface Control: Performance and Training Effects

Individuals with high spinal cord injuries are unable to operate a keyboard and mouse with their hands. In this experiment, we compared two systems using surface electromyography (sEMG) recorded from facial muscles to control an onscreen keyboard to type five-letter words. Both systems used five sEMG sensors to capture muscle activity during five distinct facial gestures that were mapped to five cursor commands: move left, move right, move up, move down, and "click". One system used a discrete movement and feedback algorithm in which the user produced one quick facial gesture, causing a corresponding discrete movement to an adjacent letter. The other system was continuously updated and allowed the user to control the cursor's velocity by relative activation between different sEMG channels. Participants were trained on one system for four sessions on consecutive days, followed by one crossover session on the untrained system. Information transfer rates (ITRs) were high for both systems compared to other potential input modalities, both initially and with training (Session 1: 62.1 bits/min, Session 4: 105.1 bits/min). Users of the continuous system showed significantly higher ITRs than the discrete users. Future development will focus on improvements to both systems, which may offer differential advantages for users with various motor impairments.

Surface electromyographic control of speech synthesis

Individuals with very high spinal cord injuries (e.g. C1-C3) may be ventilator-dependent and therefore unable to support speech breathing. However, their facial musculature is intact, given that these muscles are innervated by cranial nerves. We developed a system using surface electromyography (sEMG) recorded from facial muscles to control a phonemic interface and voice synthesizer and tested the system in healthy individuals. Users were able to use five facial gestures to control an onscreen cursor and the phonemic interface. Users had mean information transfer rates (ITRs) of 59.5 bits/min when calculating ITRs using the number of phonemes selected. To compare with orthographic systems, ITRs were also calculated using the equivalent number of letters required to spell the selected word. With this calculation, users had a mean ITR of 70.1. Results are promising for further development and testing in individuals with high spinal cord injuries.

Discrete vs. continuous surface electromyographic interface control

Over 50% of the 273,000 individuals with spinal cord injuries in the US have cervical injuries and are therefore unable to operate a keyboard and mouse with their hands. In this experiment, we compared two systems using surface electromyography (sEMG) recorded from facial muscles to control an onscreen keyboard. Both systems used five sEMG sensors to capture muscle activity during five distinct facial gestures that then mapped to five cursor commands: move left, move right, move up, move down, and click. One system used a discrete movement and feedback algorithm, in which the user would make one quick facial gesture, causing a corresponding discrete movement to an adjacent button. The other system was continuously updated and allowed the user to move in any 360(o) direction smoothly. Information transfer rates (ITRs) in bits per minute were high for both systems. Users of the continuous system showed significantly higher ITRs (average of 68.5; p <; 0.02) compared to users of the discrete system (average of 54.3 bits/min).

Normalization patterns of the surface electromyographic signal in the phonation evaluation

PURPOSE

The aim of the study was to compare the different parameters, regarding the peak and mean, at different phonatory tasks for standardization of electromyography signal of electrical activity (EA) of the laryngeal extrinsic muscles on voice evaluation.

METHODS

The electrical potentials of the suprahyoid (SH) and infrahyoid (IH) muscles of 35 voluntary nondysphonic subjects were evaluated using three evaluations of rest, two maneuvers to determine maximum voluntary sustained activity (MVSA), and usual and strong intensity of vowel /ɛ/ and 20-30 count emissions. The EA signal was converted using root mean square in microvolts and normalized by mean and peak of each task. The selected normalization task was that with minor coefficient of variation for all muscles.

RESULTS

The tasks that provided minor coefficient of variation of EA in both muscle groups were the peak of vowel /ɛ/ (mean potentials equal to 43.31 ± 2.97 for right IH, 36.27 ± 2.76 for left IH, and 42.11 ± 2.57 for SH) and the 20-30 count emissions (mean potentials equal to 31.30 ± 308 for right IH, 30.56 ± 2.76 for left IH, and 30.43 ± 4.22 for SH), both in usual intensity and MVSA, as second option.

CONCLUSIONS

The peak of vowel /ɛ/ and 20-30 count emissions is usual intensity, and the MVSA as second option should be considered for signal normalization in SH and IH muscles, and may provide conditions for using the surface electromyography in voice clinic.

Effects of augmentative visual training on audio-motor mapping

The purpose of this study was to determine the effect of augmentative visual feedback training on auditory-motor performance. Thirty-two healthy young participants used facial surface electromyography (sEMG) to control a human-machine interface (HMI) for which the output was vowel synthesis. An auditory-only (AO) group (n=16) trained with auditory feedback alone and an auditory-visual (AV) group (n=16) trained with auditory feedback and progressively-removed visual feedback. Subjects participated in three training sessions and one testing session over 3days. During the testing session they were given novel targets to test auditory-motor generalization. We hypothesized that the auditory-visual group would perform better on the novel set of targets than the group that trained with auditory feedback only. Analysis of variance on the percentage of total targets reached indicated a significant interaction between group and session: individuals in the AV group performed significantly better than those in the AO group during early training sessions (while using visual feedback), but no difference was seen between the two groups during later sessions. Results suggest that augmentative visual feedback during training does not improve auditory-motor performance.

Oral electromyography activation patterns for speech are similar in preschoolers who do and do not stutter

PURPOSE

In this study, the authors determined whether basic patterns of muscle activation for speech were similar in preschool children who stutter and in their fluent peers.

METHOD

Right and left lower lip muscle activity were recorded during conversational speech and sentence repetition in 64 preschool children diagnosed as stuttering (CWS) and in 40 children who do not stutter (CWNS). Measures of electromyography (EMG) amplitude, right-left asymmetry, and bilateral coordination were computed for fluent speech. The potential presence of tremor-like oscillations during disfluencies of CWS was assessed, and EMG amplitudes of fluent and disfluent speech were compared in CWS.

RESULTS

Across both speaking tasks, lip muscle activation was similar in CWS and CWNS in overall amplitude, bilateral synchrony, and degree of right-left asymmetry. EMG amplitude was reduced during disfluent compared with fluent conversational speech of CWS, and there was no evidence of tremor in the disfluencies of CWS.

CONCLUSION

These results support the assertion that stuttering in young children arises not from basic features of muscle contraction but rather from the command signals that control the timing and amplitude of muscle activity. The results indicate that no frank abnormality is present in muscle activation patterns in preschoolers who stutter.

Combined Auditory and Vibrotactile Feedback for Human-Machine-Interface Control

The purpose of this study was to determine the effect of the addition of binary vibrotactile stimulation to continuous auditory feedback (vowel synthesis) for human-machine interface (HMI) control. Sixteen healthy participants controlled facial surface electromyography to achieve 2-D targets (vowels). Eight participants used only real-time auditory feedback to locate targets whereas the other eight participants were additionally alerted to having achieved targets with confirmatory vibrotactile stimulation at the index finger. All participants trained using their assigned feedback modality (auditory alone or combined auditory and vibrotactile) over three sessions on three days and completed a fourth session on the third day using novel targets to assess generalization. Analyses of variance performed on the 1) percentage of targets reached and 2) percentage of trial time at the target revealed a main effect for feedback modality: participants using combined auditory and vibrotactile feedback performed significantly better than those using auditory feedback alone. No effect was found for session or the interaction of feedback modality and session, indicating a successful generalization to novel targets but lack of improvement over training sessions. Future research is necessary to determine the cognitive cost associated with combined auditory and vibrotactile feedback during HMI control.

Use of surface electromyography in phonation studies: an integrative review

INTRODUCTION

Surface electromyography has been used to assess the extrinsic laryngeal muscles during chewing and swallowing, but there have been few studies assessing these muscles during phonation.

OBJECTIVE

 To investigate the current state of knowledge regarding the use of surface electromyography for evaluation of the electrical activity of the extrinsic muscles of the larynx during phonation by means of an integrative review.

METHOD

 We searched for articles and other papers in the PubMed, Medline/Bireme, and Scielo databases that were published between 1980 and 2012, by using the following descriptors: surface electromyography and voice, surface electromyography and phonation, and surface electromyography and dysphonia. The articles were selectedon the basis ofinclusion and exclusion criteria.

DATA SYNTHESIS

 This was carried out with a cross critical matrix. We selected 27 papers,i.e., 24 articles and 3 theses. The studies differed methodologically with regards to sample size and investigation techniques, making it difficult to compare them, but showed differences in electrical activity between the studied groups (dysphonicsubjects, non-dysphonicsubjects, singers, and others).

CONCLUSION

 Electromyography has clinical applicability when technical precautions with respect to application and analysis are obeyed. However, it is necessary to adopt a universal system of assessment tasks and related measurement techniques to allow comparisons between studies.