Facial reactions to auditory stimuli: Sex differences

This study explored whether males and females differ in facial muscle activity when exposed to tone stimuli with different intensity. Males and females were repeatedly exposed to 95 dB and 75 dB 1000 Hz tones while their facial electromyographic (EMG) activity from corrugator and zygomatic muscle regions were measured. Skin conductance responses were also measured. It was found that 95 dB but not 75 dB tones evoked increased corrugator activity. This effect differed significantly between males and females. Thus, it was only females that reacted with a significant increased corrugator response to the high intensity tone. While facial responses differed between the sexes, the skin conductance response patterns did not. Consistent with previous research it is concluded that females are more facially expressive than are males.     

Facial EMG reactions to facial expressions: A case of facial emotional contagion?

The purpose of this study is to explore whether subjects exposed to stimuli of facial expressions respond with facial electromyographic (EMG) reactions consistent with the hypothesis that facial expressions are contagious. This study further examines whether males and females differ in facial EMG intensity. Two experiments demonstrated that subjects responded with facial EMG activity over the corrugator supercilii, the zygomatic major , the lateral frontalis , the depressor supercilii , and the levator labii muscle regions to stimuli of sad, angry, fearful, surprised, disgusted and happy faces, that, to large extent, were consistent with the hypothesis that facial expressions are contagious. Aspects of gender differences reported in earlier studies were found, indicating a tendency for females to respond with more pronounced facial EMG intensity.     

EMG Activity as a Function of the Performer's Focus of Attention

In previous studies of attentional focus effects, investigators have measured performance outcome. Here, however, the authors used electromyography (EMG) to determine whether differences between external and internal foci would also be manifested at the neuromuscular level. In 2 experiments, participants (N = 11, Experiment 1; N = 12, Experiment 2) performed biceps curls while focusing on the movements of the curl bar (external focus) or on their arms (internal focus). In Experiment 1, movements were performed faster under external than under internal focus conditions. Also, integrated EMG (iEMG) activity was reduced when performers adopted an external focus. In Experiment 2, movement time was controlled through the use of a metronome, and iEMG activity was again reduced under external focus conditions. Those findings are in line with the constrained action hypothesis (G. Wulf, N. McNevin, & C. H. Shea, 2001), according to which an external focus promotes the use of more automatic control processes.     

Muscle Synergies for Turning During Human Walking

Muscle synergy describes reduced set of functional muscle co-activation patterns. We aimed to identify muscle synergies of turning compared with straight walking. Twelve healthy adults (men: 7, women: 5) performed straight walking (SW), left turning (LT), and right turning (RT) at self-selected speeds. By using non-negative matrix factorization (NMF), we extracted muscle synergies from sixteen electromyography (EMG) signals on the right side and assigned similar muscle synergies among SW, LT, and RT into the same cluster by combining k-means clustering and intraclass correlation coefficient (ICC) analysis. We obtained task-specific clusters of muscle synergies extracted from SW, LT, or RT condition and identified the clusters that share synergies among the conditions. The central nervous system produces specific synergies involving turning behaviors and fundamental synergies for walking.     

Modular Organization of Exploratory Force Development Under Isometric Conditions in the Human Arm

Muscle coordination of isometric force production can be explained by a smaller number of modules. Variability in force output, however, is higher during exploratory/transient force development phases than force maintenance phase, and it is not clear whether the same modular structure underlies both phases. In this study, eight neurologically-intact adults isometrically performed target force matches in 54 directions at hands, and electromyographic (EMG) data from eight muscles were parsed into four sequential phases. Despite the varying degree of motor complexity across phases (significant between-phase differences in EMG-force correlation, angular errors, and between-force correlations), the number/composition of motor modules were found equivalent across phases, suggesting that the CNS systematically modulated activation of the same set of motor modules throughout sequential force development.     

The coordination of shoulder girdle muscles during repetitive arm movements at either slow or fast pace among women with or without neck-shoulder pain

Purpose: The aim of this study was to evaluate the coordination of the shoulder girdle muscles among subjects with or without neck-shoulder pain performing repetitive arm movement at either a slow or fast pace. Methods: Thirty female adults were allocated to one of two groups—healthy controls or cases with neck-shoulder pain. Surface electromyography (sEMG) signals from the clavicular, acromial, middle and lower trapezius portions and the serratus anterior muscles were recorded during a task performed for 20 min at a slow pace and 20 min at a fast pace. The root mean square (RMS), relative rest time (RRT) and normalised mutual information (NMI, an index of functional connectivity between two muscles in a pair) were computed. Results: No significant differences on RMS, RRT and NMI were found between groups. For both groups, the fast movement pace resulted in increased levels of RMS, lower degrees of RRT and higher NMI compared to the slow pace. No interaction between group and movement pace was found. Conclusions: This study highlights the change in sEMG activity of muscles to meet the demands of performing a task at fast movement pace. The fast pace imposed a higher muscle demand evidenced by increased sEMG amplitude, low degree of muscle rest and increased functional connectivity for subjects in both the case and control groups. No indication of impaired sEMG activity was found in individuals with neck-shoulder pain.     

Social fear and expressive reactions to social stimuli

This study explored whether subjects high as compared to low in social fear react with a more negative emotional response, measured as facial electromyographic (EMG) activity, when exposed to social stimuli (pictures of angry and happy facial expressions). It was found that subjects who rated themselves as relatively high in public speaking fear gave larger negative facial EMG responses (Corrugator supercilii muscle activity) to angry faces than did the low fear subjects. Low fear subjects, on the other hand, gave larger positive facial EMG responses (Zygomatic major muscle activity) to happy faces than did the high fear subjects. It was further found that happy stimuli were rated as more hostile and less friendly and happy by the high fear group. Consistent with earlier findings, it was concluded that the facial EMG technique is sensitive to detecting different reactions among subjects relatively high and low in social fear.     

OPERANT TREATMENT OF OROFACIAL DYSFUNCTION IN NEUROMUSCULAR DISORDERS

The popularity and reported success of biofeedback treatment for neuromuscular disorders has occurred despite a lack of research identifying the critical variables responsible for therapeutic gain. In this study, we assessed the degree to which severe neurological dysfunction could be improved by using one of the components present in all biofeedback treatment, contingency management. Three cases of orofacial dysfunction were treated by reinforcing specific improvements reliably detectable without the use of biofeedback equipment. The results showed that contingency management procedures alone were sufficient to improve overt motor responses but, unlike biofeedback treatment, did not produce decreases in the hypertonic muscle groups associated with the trained motor behavior. The findings suggest that sophisticated, expensive biofeedback equipment may not be necessary in treating some neuromuscular disorders and that important clinical gains may be achieved by redesigning the patient's daily environment to be contingently therapeutic, rather than only accommodating the disabilities of the physically handicapped.     

When smiles (and frowns) speak words: Does power impact the correspondence between self-reported affect and facial expressions?

Self-reported experiences are often poor indicators of outward expressions. Here we examine social power as a variable that may impact the relationship between self-reported affect and facial expressions. Earlier studies addressing this issue were limited by focusing on a single facial expression (smiling) and by using different, less sensitive methods that yielded mostly null results. Sampling, for the first time, self-reported affect repeatedly in response to different negative, neutral and positive stimuli, and measuring concurrent facial muscle activation via electromyography, we found that high power (vs. baseline) increased the correspondence between self-reported positive affect and smiling. There was also an indication that high power (vs. baseline) bolstered the association between self-reported negative affect and frowning but the effect did not pass more stringent criteria for significance (p ≤ .005) and was therefore deemed inconclusive. The prediction that low power (vs. baseline) decreases the correspondence between self-reported affect and smiling and frowning facial expressions was not supported. Taken together, it would appear that (high) power can impact the relationship between self-reported affect and facial expressions, but it remains to be seen whether this effect extends beyond smiling facial expressions.     

Effects of muscle fatigue on the usability of a myoelectric human-computer interface

Electromyography-based human-computer interface development is an active field of research. However, knowledge on the effects of muscle fatigue for specific devices is limited. We have developed a novel myoelectric human-computer interface in which subjects continuously navigate a cursor to targets by manipulating a single surface electromyography (sEMG) signal. Two-dimensional control is achieved through simultaneous adjustments of power in two frequency bands through a series of dynamic low-level muscle contractions. Here, we investigate the potential effects of muscle fatigue during the use of our interface. In the first session, eight subjects completed 300 cursor-to-target trials without breaks; four using a wrist muscle and four using a head muscle. The wrist subjects returned for a second session in which a static fatiguing exercise took place at regular intervals in-between cursor-to-target trials. In the first session we observed no declines in performance as a function of use, even after the long period of use. In the second session, we observed clear changes in cursor trajectories, paired with a target-specific decrease in hit rates.