Attribution of sensory prediction error to perception of muscle fatigue.

Sensory prediction-error is vital to discriminating whether sensory inputs are caused externally or are the consequence of self-action, thereby contributing to a stable perception of the external world and building sense of agency. However, it remains unexplored whether prediction error of self-action is also used to estimate the internal body condition. To address this point, we examined whether prediction error affects the perceived intensity of muscle fatigue. Participants evaluated fatigue while maintaining repetitive finger movements. To provide prediction error, we inserted a temporal delay into online visual feedback of self-movements. The results show that the subjective rating of muscle fatigue significantly increased under the delayed visual feedback, suggesting that prediction error enhances the perception of muscle fatigue. Furthermore, we introduced visual feedback that preceded actual finger movements to test whether the temporal direction of the mismatch is crucial in estimating muscle fatigue. We found that perceived fatigue was significantly weaker with preceding visual feedback compared to normal feedback, showing that the perception of muscle fatigue is affected by the signed prediction-error. Our findings support the idea that the brain flexibly attributes prediction errors to a self-origin with keeping sense of agency, or external origin by considering contexts and error characteristics.

Compensative movement ameliorates reduced efficacy of rapidly-embodied decisions in humans.

Dynamic environments, such as sports, often demand rapid decision-making and motor execution. The concept of embodied decision refers to the mutual link between both processes, but little is known about how these processes are balanced under severe time constraints. We address this problem by using a baseball-like hitting paradigm with and without Go/No-go judgment; participants were required to hit (Go) a moving target in the strike area or not to hit (No-go) other targets. We found that Go/No-go judgments were effective with regard to task performance, but efficacy was lost below the time constraint of 0.5 seconds mainly due to a reduction in judgment accuracy rather than movement accuracy. However, either slowing movement initiation in Go trials or canceling the movement in progress in No-go trials improved judgment accuracy. Our findings suggest that embodied decision efficacy is limited in split-second periods, but compensation is possible by changing ongoing movement strategies.

Positive Relationship Between Precompetitive Sympathetic Predominance and Competitive Performance in Elite Extreme Sports Athletes.

Elite athletes achieve superior performance under high pressure in competitive situations. Although it is known that such situations affect the precompetitive activity of their autonomic nervous system (ANS), the relationship between precompetitive ANS activity and performance remains controversial. Especially in extreme sports, it has been shown that cardiac sympathetic tone occurs in athletes before competition attempts. However, the relationship between precompetitive sympathetic tone and performance is unclear. To investigate this relationship in extreme sports, we organized a freestyle snowboard jumping competition and examined competitors' physiological states and performance during this event. The electrocardiograms (ECGs) of 20 elite snowboarders were measured 10 min before each jump in different competitive situations: practice, qualifying, and final sessions. The mean heart rate (HR), the low-frequency to high-frequency component ratio (LF/HF ratio), the logarithm of the HF (lnHF) component of the frequency-domain of the heart rate variability (HRV), the ratio of the standard deviation of all R-R intervals to the root mean square of successive differences of R-R intervals (SDNN/rMSSD ratio), and the rMSSD of the time-domain of the HRV were calculated from the ECG data. The results showed a significant increase in the mean HR as well as significant decreases in the lnHF component and rMSSD of the HRV as the sessions progressed. Interestingly, the mean HR, LF/HF ratio and SDNN/rMSSD ratio of the HRV showed significant positive correlations with competitive scores, and the lnHF component and rMSSD of the HRV showed significant negative correlations with the scores. Our results indicate that precompetitive ANS activity becomes predominantly sympathetic in elite extreme athletes, such as freestyle snowboarders, when the competition intensifies, and that this sympathetic predominance is positively related to competitive performance.

Comfortable and Convenient Turning Skill Assessment for Alpine Skiers Using IMU and Plantar Pressure Distribution Sensors.

Improving ski-turn skills is of interest to both competitive and recreational skiers, but it is not easy to improve on one's own. Although studies have reported various methods of ski-turn skill evaluation, a simple method that can be used by oneself has not yet been established. In this study, we have proposed a comfortable method to assess ski-turn skills; this method enables skiers to easily understand the relationship between body control and ski motion. One expert skier and four intermediate skiers participated in this study. Small inertial measurement units (IMUs) and mobile plantar pressure distribution sensors were used to capture data while skiing, and three ski-turn features-ski motion, waist rotation, and how load is applied to the skis-as well as their symmetry, were assessed. The results showed that the motions of skiing and the waist in the expert skier were significantly larger than those in intermediate skiers. Additionally, we found that the expert skier only slightly used the heel to apply a load to the skis (heel load ratio: approximately 60%) and made more symmetrical turns than the intermediate skiers did. This study will provide a method for recreational skiers, in particular, to conveniently and quantitatively evaluate their ski-turn skills by themselves.

Behavioral Measures in a Cognitive-Motor Batting Task Explain Real Game Performance of Top Athletes.

Excellent athletic performance in baseball and softball batting is achieved through the momentary cognitive-motor processes. However, in previous studies, cognitive and motor processes are investigated separately. In this study, we focused on the difference in the time of swing onset (a delta onset) during a batting task where 17 elite female softball batters hit balls randomly thrown at two different speeds by pitchers. The delta onset included both cognitive and motor processes because the batters needed to anticipate the ball speed and discriminate their swing motion according to the time-to-contact. Then, we investigated the relationship between the delta onset and the batting outcomes of the batting task, and the relationship between the experimental outcomes and actual batting performance (batting average) over a season. We used path analysis to clarify the structure of the cognitive-motor processes and consequent performance. We found that the batters who had a larger delta onset attained superior batting outcomes (i.e., higher exit velocity and lower miss ratio) in the batting task, and these experimental outcomes explained 67% of the batting average in real games. On the other hand, the cognitive scores (judgement accuracy and rapidity) obtained from a button pressing task, where batters responded to a ball by pressing a button instead of actually swinging, explained only 34% of the batting average. Therefore, our model quantitatively describes the key cognitive-motor structure for athletes and can partially predict a batter's performance in real games. These findings suggest that it is important to employ both cognitive and motor processes in performing tasks, such as this batting task, to properly evaluate a batter's actual ability.

Walking and talking independently predict interpersonal impressions.

When walking alongside someone, you may feel that your legs move in synchrony with theirs. Recent studies have shown that walk-in-synch behaviour observed in natural settings occurs at a rate significantly greater than would be expected by chance, and that the amount of this synchrony is related to interpersonal impressions. However, in such natural settings, the existence of verbal conversations between paired walkers should affect the interpersonal impressions and the effect is not distinguished from the effect of walk-in-synch on the impressions so far. In the current study, we used the analysis of conversation and path analysis to discriminate these two effects (i.e., the effects of synchronization of walking and conversation on interpersonal impressions). Analysis of conversation during the walk revealed that the amount of utterance overlap and the number of turn-takings between two walkers as well as the synchronization of steps predicted their positive interpersonal impression, while synchronization of steps and these two conversational indices were not correlated with each other. We propose that interpersonal synchronization of body movements, such as synchronization of steps itself in paired walking, plays a role in fostering the development of interpersonal relationships.

Sock-Type Wearable Sensor for Estimating Lower Leg Muscle Activity Using Distal EMG Signals.

Lower leg muscle activity contributes to body control; thus, monitoring lower leg muscle activity is beneficial to understand the body condition and prevent accidents such as falls. Amplitude features such as the mean absolute values of electromyography (EMG) are used widely for monitoring muscle activity. Garment-type EMG measurement systems use electrodes and they enable us to monitor muscle activity in daily life without any specific knowledge and the installation for electrode placement. However, garment-type measurement systems require a high compression area around the electrodes to prevent electrode displacement. This makes it difficult for users to wear such measurement systems. A less restraining wearable system, wherein the electrodes are placed around the ankle, is realized for target muscles widely distributed around the shank. The signals obtained from around the ankle are propagated biosignals from several muscles, and are referred to as distal EMG signals. Our objective is to develop a sock-type wearable sensor for estimating lower leg muscle activity using distal EMG signals. We propose a signal processing method based on multiple bandpass filters from the perspectives of noise separation and feature augmentation. We conducted an experiment for designing the hardware configuration, and three other experiments for evaluating the estimation accuracy and dependability of muscle activity analysis. Compared to the baseline based on a 20-500 Hz bandpass filter, the results indicated that the proposed system estimates muscle activity with higher accuracy. Experimental results suggest that lower leg muscle activity can be estimated using distal EMG signals.

Lower Limb Muscle Activity Control by using Jamming Footwear.

To change the lower limb muscle activities while walking, we propose a muscle activity controlling system that dynamically changes shoe insoles. We conducted a preliminary experiment on a prototype system to determine the system's validity. In this experiment, we analyzed how tibialis anterior and gastrocnemius muscle might change their activities depending on each insole condition. The results lead us to conclude that our system may affect changes in the duration percentage of tibialis anterior muscle activation when we change the heel part shape, and that it may change the maximum amplitude of gastrocnemius muscle activation when we change the arch part shape and hardness.

Audio-tactile cues from an object's fall change estimates of one's body height.

When we drop an object from our hands, we use internal models of both our body height and object-motion to predict when it will hit the floor. What happens if the sensory feedback finally received from the impact conflicts with this prediction? The present study shows that such conflict results in changes in the internal estimates of our body height: When the object people dropped takes longer than expected to hit the floor, they report feeling taller and behave as if their legs were longer. This provides the first evidence of cross-modal recalibration of body-height representations as a function of changes in the distant environment. Crucially, the recalibration results from a mismatch between the predicted and actual outcome of an action, the ball's release and impact, which are causally-related but separated in space and time. These results suggest that implicit models of object-motion can interact with implicit and explicit models of one's body height.

Characterizing muscular activities using non-negative matrix factorization from EMG channels for driver swings in golf.

The goal of this study is to propose a data driven approach method to characterize muscular activities of complex actions in sports such as golf from a lot of EMG channels. Two problems occur in a many channel measurement. The first problem is that it takes a lot of time to check the many channel data because of combinatorial explosion. The second problem is that it is difficult to understand muscle activities related with complex actions. To solve these problems, we propose an analysis method of multi EMG channels using Non-negative Matrix Factorization and adopt the method to driver swings in golf. We measured 26 EMG channels about 4 professional coaches of golf. The results show that the proposed method detected 9 muscle synergies and the activation of each synergy were mostly fitted by sigmoid curve (R2=0.85).

Speech misperception: speaking and seeing interfere differently with hearing.

Speech perception is thought to be linked to speech motor production. This linkage is considered to mediate multimodal aspects of speech perception, such as audio-visual and audio-tactile integration. However, direct coupling between articulatory movement and auditory perception has been little studied. The present study reveals a clear dissociation between the effects of a listener's own speech action and the effects of viewing another's speech movements on the perception of auditory phonemes. We assessed the intelligibility of the syllables [pa], [ta], and [ka] when listeners silently and simultaneously articulated syllables that were congruent/incongruent with the syllables they heard. The intelligibility was compared with a condition where the listeners simultaneously watched another's mouth producing congruent/incongruent syllables, but did not articulate. The intelligibility of [ta] and [ka] were degraded by articulating [ka] and [ta] respectively, which are associated with the same primary articulator (tongue) as the heard syllables. But they were not affected by articulating [pa], which is associated with a different primary articulator (lips) from the heard syllables. In contrast, the intelligibility of [ta] and [ka] was degraded by watching the production of [pa]. These results indicate that the articulatory-induced distortion of speech perception occurs in an articulator-specific manner while visually induced distortion does not. The articulator-specific nature of the auditory-motor interaction in speech perception suggests that speech motor processing directly contributes to our ability to hear speech.

Ketamine eliminates propofol pain but does not affect hemodynamics during induction with double-lumen tubes.

BACKGROUND AND OBJECTIVE: Propofol injection during induction of anesthesia induces pain. Ketamine has been shown to reduce the injection pain. However, ketamine has unfavorable adverse effects, including increased secretion production and hemodynamic responses, which might induce pulmonary or hemodynamic adverse events, especially in patients undergoing lung surgery who require a double-lumen tube (DLT). The aim of this study was to determine whether ketamine can safely reduce propofol injection pain during induction of anesthesia for lung surgery. METHODS: Forty-five patients scheduled for elective lung surgery requiring DLT were randomly allocated into three groups. Patients received saline (control), ketamine 0.5 mg kg(-1) (0.5 ketamine), or ketamine 1.0 mg kg(-1) (1.0 ketamine), followed by 5 ml propofol 30 s later. An anesthesiologist blinded to the study group assessed pain score during induction, hemodynamics during DLT placement, and secretion production during anesthetic management. RESULTS: Pretreatment of 0.5 mg kg(-1) ketamine reduced the incidence and intensity of propofol injection pain, whereas 1.0 mg kg(-1) ketamine completely eliminated the pain. There were no significant differences regarding oxygenation during one-lung ventilation (OLV) and hemodynamics during induction among the three groups, although ketamine increased secretion production. CONCLUSIONS: One milligram per kilogram of ketamine completely eliminated pain associated with propofol injection without affecting hemodynamics during induction of anesthesia and oxygenation during OLV.

Temporal development of anticipatory reflex modulation to dynamical interactions during arm movement.

It is known that somatosensory reflex during voluntary arm movement is modulated anticipatorily according to given tasks or environments. However, when and how reflex amplitude is set remains controversial. Is the reflex modulation completed preparatorily before movement execution or does it vary with the movement? Is the reflex amplitude coded in a temporal manner or in a spatial (or state-dependent) manner? Here we studied these issues while subjects performed planar reaching movements with upcoming opposite (rightward/leftward) directions of force fields. Somatosensory reflex responses of shoulder muscles induced by a small force perturbation were evaluated at several points before the arm encountered predictable force fields after movement start. We found that the shoulder flexor reflex responses were generally higher for the rightward than for the leftward upcoming force fields, whereas the extensor reflex responses were higher for the leftward force field. This reflex amplitude depending on the upcoming force field direction became prominent as the reflex was evoked closer to the force fields, indicating continuous changes in reflex modulation during movement. An additional experiment further showed that the reflex modulation developed as a function of the temporal distance to the force fields rather than the spatial distance. Taken together, the results suggest that, in the force field interaction task, somatosensory reflex amplitude during the course of movement is set anticipatorily on the basis of an estimate of the time-to-contact rather than the state-to-contact, to upcoming dynamical interaction during voluntary movement.

Odd sensation induced by moving-phantom which triggers subconscious motor program.

Our motor actions are sometimes not properly performed despite our having complete understanding of the environmental situation with a suitable action intention. In most cases, insufficient skill for motor control can explain the improper performance. A notable exception is the action of stepping onto a stopped escalator, which causes clumsy movements accompanied by an odd sensation. Previous studies have examined short-term sensorimotor adaptations to treadmills and moving sleds, but the relationship between the odd sensation and behavioral properties in a real stopped-escalator situation has never been examined. Understanding this unique action-perception linkage would help us to assess the brain function connecting automatic motor controls and the conscious awareness of action. Here we directly pose a question: Does the odd sensation emerge because of the unfamiliar motor behavior itself toward the irregular step-height of a stopped escalator or as a consequence of an automatic habitual motor program cued by the escalator itself. We compared the properties of motor behavior toward a stopped escalator (SE) with those toward moving escalator and toward a wooden stairs (WS) that mimicked the stopped escalator, and analyzed the subjective feeling of the odd sensation in the SE and WS conditions. The results show that moving escalator-specific motor actions emerged after participants had stepped onto the stopped escalator despite their full awareness that it was stopped, as if the motor behavior was guided by a "phantom" of a moving escalator. Additionally, statistical analysis reveals that postural forward sway that occurred after the stepping action is directly linked with the odd sensation. The results suggest a dissociation between conscious awareness and subconscious motor control: the former makes us perfectly aware of the current environmental situation, but the latter automatically emerges as a result of highly habituated visual input no matter how unsuitable the motor control is. This dissociation appears to yield an attribution conflict, resulting in the odd sensation.

Close similarity between spatiotemporal frequency tunings of human cortical responses and involuntary manual following responses to visual motion.

Human brain uses visual motion inputs not only for generating subjective sensation of motion but also for directly guiding involuntary actions. For instance, during arm reaching, a large-field visual motion is quickly and involuntarily transformed into a manual response in the direction of visual motion (manual following response, MFR). Previous attempts to correlate motion-evoked cortical activities, revealed by brain imaging techniques, with conscious motion perception have resulted only in partial success. In contrast, here we show a surprising degree of similarity between the MFR and the population neural activity measured by magnetoencephalography (MEG). We measured the MFR and MEG induced by the same motion onset of a large-field sinusoidal drifting grating with changing the spatiotemporal frequency of the grating. The initial transient phase of these two responses had very similar spatiotemporal tunings. Specifically, both the MEG and MFR amplitudes increased as the spatial frequency was decreased to, at most, 0.05 c/deg, or as the temporal frequency was increased to, at least, 10 Hz. We also found in peak latency a quantitative agreement (approximately 100-150 ms) and correlated changes against spatiotemporal frequency changes between MEG and MFR. In comparison with these two responses, conscious visual motion detection is known to be most sensitive (i.e., have the lowest detection threshold) at higher spatial frequencies and have longer and more variable response latencies. Our results suggest a close relationship between the properties of involuntary motor responses and motion-evoked cortical activity as reflected by the MEG.

Transcranial magnetic stimulation over sensorimotor cortex disrupts anticipatory reflex gain modulation for skilled action.

Skilled interactions with new environments require flexible changes to the transformation from somatosensory signals to motor outputs. Transcortical reflex gains are known to be modulated according to task and environmental dynamics, but the mechanism of this modulation remains unclear. We examined reflex organization in the sensorimotor cortex. Subjects performed point-to-point arm movements into predictable force fields. When a small perturbation was applied just before the arm encountered the force field, reflex responses in the shoulder muscles changed according to the upcoming force field direction, indicating anticipatory reflex gain modulation. However, when a transcranial magnetic stimulation (TMS) was applied before the reflex response to such perturbations so that the silent period caused by TMS overlapped the reflex processing period, this modulation was abolished, while the reflex itself remained. Loss of reflex gain modulation could not be explained by reduced reflex amplitudes nor by peripheral effects of TMS on the muscles themselves. Instead, we suggest that TMS disrupted interneuronal networks in the sensorimotor cortex, which contribute to reflex gain modulation rather than reflex generation. We suggest that these networks normally provide the adaptability of rapid sensorimotor reflex responses by regulating reflex gains according to the current dynamical environment.

The motor cortex is involved in reflexive compensatory adjustment of speech articulation.

Although speech articulation relies heavily on the sensorimotor processing, little is known about its brain control mechanisms. Here, we investigate, using transcranial magnetic stimulation, whether the motor cortex contributes to the generation of quick sensorimotor responses involved in speech motor coordination. By applying a jaw-lowering perturbation, we induced a reflexive compensatory upper-lip response, which assists in maintaining the intact labial aperture in the production of bilabial fricative consonants. This reflex response was significantly facilitated by subthreshold transcranial magnetic stimulation over the motor cortex, whereas a simple perioral reflex that is mediated only within the brainstem was not. This suggests that the motor cortex is involved in generating this functional reflexive articulatory compensation.

Anticipatory modulation of neck muscle reflex responses induced by mechanical perturbations of the human forehead.

The aim of this study was to test whether anticipation of upcoming head blow stimuli, which elicit reflex responses in the neck muscle, makes the reflex responses greater or not. In nine healthy subjects the reflex responses were elicited in the sternocleidomastoid (SCM) muscle in the eyes-open (EO) and eyes-closed (EC) conditions, which corresponded to the predictable and unpredictable conditions, respectively. The subjects were instructed not to resist the perturbations after the impact. The results demonstrated that the reflex response of the SCM muscle was significantly smaller in the predictable EO condition than in the unpredictable EC condition (P < 0.05), although no significant differences were observed in either the background EMG activities or the head accelerations. Further, this effect of anticipation was observed only in the later reflex EMG component, which most probably mediated the stretch reflex pathway. In contrast, no significant difference was observed in the early component, which was presumed to be the vestibular-collic reflex. The reduced stretch reflex response was suggested to be functionally relevant to the task requirement, i.e., to let the neck extension movement occur, and not to resist after the impact of the head blow. It was concluded that the anticipation has an effect on reducing the stretch reflex responses in the neck muscle, but does not have any effect on the presumed vestibular-collic reflex under the present experimental paradigm. It is suggested that the gain of the stretch reflex pathway is modulated by anticipatory information of upcoming mechanical event.

Selective activation and deactivation of the human brain structures between speeded and precisely timed tapping responses to identical visual stimulus: an fMRI study.

We investigated the difference between brain activities in speeded and precisely timed responses to identical visual stimulus using fMRI. Stimulus used was a row of seven light-emitting diodes (LEDs) lightened up one after another with constant speed within a trial but with various speeds between trials. Subjects were asked to execute finger-thumb tapping with the right hand in response to the onset of the first LED light in the reaction time (RT) task and in anticipation of the onset of the last (i.e., seventh) LED light in the timing task. In control condition, they were asked to passively view the stimulus without motor response. Results showed that various movement-related areas including contralateral cingulate motor cortex were commonly activated for both tasks relative to the control condition, suggesting these structures are involved in general perception and response execution rather than specific function for speeded or precisely timed responses. In the RT task, the presupplementary motor area extending to the cingulate sulcus was activated more strongly than in the timing task probably to focus attention to the onset of the first LED light unpredictably presented after random foreperiods. The lateral occipital area extending to the temporo-parieto-occipital junction was activated more strongly in the timing task than in the RT task; the same area was deactivated in the RT task relative to the control condition. Auditory-related areas were also deactivated in the both tasks. This inter- and intramodal task-specific modification including deactivation underscores significance of the context for perception and action and can have an important role in dexterous or skilled performance.