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In human motion capture systems, reflective markers attached to the body have been widely used to track motion using optical cameras. However, when the speed of motion increases, because the brightness and angle of view of the camera are limited, and the markers often fall off, particularly of detailed body parts such as fingers in full-body movements, other parts of the body (palms) have been investigated. This study attempted to acquire finger movements during a high-speed throwing task without attaching markers using automatic image recognition technology based on deep learning (DeepLabCut) and verified its accuracy compared to conventional methods. As a result, the absolute distance between the 3D coordinates obtained from the two motion capture systems was an average of 15.5 to 29.4 mm depending on tracked points, and the correlation coefficients between them ranged from 0.932 to 0.999. Therefore, the shapes of the time-series profiles of the 3D coordinates obtained from the two motion- capture systems were similar. These results suggest that motion measurement using markerless motion capture is possible in environments where conventional motion capture systems are difficult to use.

Repeated and accurate throwing of an object to a target position is a special human motor skill. It is particularly important to understand accuracy, which has received less attention than speed due to difficulties in measurement. Accuracy has been studied in terms of reducing errors against a single target, but also in terms of distinguishing appropriate throws for targets in different positions. In this study, this ability was investigated by evaluating the two-dimensional distributions of the pitch locations of 15 pitches to three target positions in university students with and without baseball experience. The center, major and minor axis length, major and minor axis ratio, slope, area, and percentage of overlapping area of the 95% confidence ellipse were compared between target positions and participants using a two-way repeated-measures analysis of variance (ANOVA). The center and area of the ellipse indicate the mean and variability of the error, respectively. The lengths of the major axes correspond to the variability of the release timing, and the minor axes correspond to the variability of the release point in space. Therefore, the ratio of the major and minor axes indicates how the variability of the pitching motion is controlled. The slope of the ellipse corresponds to the throwing arm's trajectory, and the percentage of overlap area means the ability to distinguish throws at different target positions. The result showed a main effect of participants on all indices except the center of the ellipse. This indicates that participants can generally distinguish throws by target positions regardless of their baseball experience, although participants with baseball experience may naturally reduce variability. Furthermore, participants with baseball experience demonstrated a decrease variability in release timing, which is a primary contributor to the pitch location variability, relative to the spatial variability of the pitching movements. This reduction in timing variability may be attributed to advanced motor control mechanisms.

Abstract Thoracic and abdominal movements can be tightly coupled during voluntary breathing, such as when singing and playing wind instruments. The present study investigated the coordination of thoracic and abdominal movements during voluntary breathing using a dynamical systems approach. We examined whether there are two stable coordination patterns, and if the coordination pattern would abruptly change when the breathing frequency increased, which is known as phase transition. The participants inhaled and exhaled repeatedly at 7.5, 15, 30, 60, or 120 breaths per minute. At the beginning and end of the experiment, the participants performed breathing at their preferred frequency. As a result, the coordination pattern at the lower and preferred frequencies exhibited an in-phase pattern. When breathing frequency increased, participants showed deviated coordination patterns from the in-phase pattern to either a thoracic-leading pattern, an abdominal-leading pattern, or an anti-phase pattern depending on the individual. These deviations occurred gradually; thus, phase transition was not observed. Our findings suggest that thoracic and abdominal movements are tightly coupled at lower frequencies, but their patterns vary depending on the breathing frequency and individuals. Therefore, the present study suggests the importance of viewing breath control in terms of coordination of thoracic and abdominal movements.

IntroductionHow does the behavior of putting things away (putting them in) in a container and using them again (taking them out) develop in young children? Though object interaction is one of the most examined topics in child development, research on organized behavior with various objects and containers at home is lacking. Rather than conducting experiments on young children's interactions with objects, this study focused on natural child–object interaction in the home.MethodsWe conducted a case study on a young child's natural interaction with objects at home, focusing on when the child puts them in or takes them out of a container (the shelf, the cabinet, or the box). The study took place over 2½ years.ResultsThe behaviors of putting many objects in a container and taking them out appeared at 9 months old. After acquiring the skill of walking, the child carried the objects using bags. Putting objects in and taking them out was embedded in the locomotion, and the child prepared the containers of toys before play. Pulling as many objects out as possible became rare after 19 months of age. Taking objects out became more appropriate in that context. The child brought out the container before the activity and put things away afterward.DiscussionBased on these findings, the development of organized object interaction as well as the anticipation and significance of the naturalistic longitudinal observations are discussed.

This study aimed to investigate the effect of footsteps of a neighboring runner (NR) on the main runner's step frequency (SF), heart rate (HR), and rating of perceived exertion (RPE). The participants were male long-distance runners belonging to a university track and field team. Two experiments were conducted in which the main runner (participant) and NR (examiner) ran with the same running speed on two adjacent treadmills separated by a thin wall. The participants were instructed that the experimental purpose was to investigate the HR when running with others and running alone. In Experiment 1, NR performed three trials of changing the footstep tempo in 5 bpm (beat per minute) faster (+5bpmFS), 5 bpm slower (-5bpmFS), or no footsteps (NF) conditions. The results showed that the footstep condition affected the variability of the SF but not the mean SF. Next, Experiment 2 was conducted by increasing the footstep tempo condition. NR performed seven trials of changing the footstep tempo by ±3 bpm, ±5 bpm, ±10 bpm, or no footstep. The results showed that the footstep condition affected the mean SF and the SF decreased at -10bpmFS compared to NF. There were no differences in the HR and RPE between conditions. These results indicated that the footsteps of NR could influence the SF, although it was unclear whether footsteps were involved in the synchronization between runners. Overall, our findings emphasize the environmental factors that influence running behavior, including the NR's footsteps.

Abstract Goal-directed movements often require choosing an option from multiple potential goals under time constraints. However, there are limited studies on how humans change their time spent on decision-making and movement patterns according to time constraints. Here, we examined how sensorimotor strategies are selected under time constraints when the target values are uncertain. In the double-target condition, the values were uncertain until the movement onset and presented immediately afterwards. The behavior in this condition was compared to the single-target condition, in relation to time constraints and target-separation-angles. The results showed that the participants frequently used the choice-reaction even under tight time constraints, and their performance was consistently lower than that in the single-target condition. Additionally, in the double-target condition, differences in the movement trajectory depending on the time constraint and target-separation angle were confirmed. Specifically, the longer the time constraint, the higher the frequency of the intermediate behavior (to initiate movement toward the intermediate direction of two targets) or the change-of-mind behavior (to change the aiming target during movement). Furthermore, the smaller the target-separation angle, the higher the frequency of intermediate behavior, but the frequency of change-of-mind was not affected by the target-separation angle. These results suggest that the participants initiated the movement at an incomplete value judgment stage in some trials. Furthermore, they seemed to select a strategy to utilize the information obtained during the movement, taking into account the time constraints and target-separation angle. Our results show a consistent cognitive bias in choosing a higher value when multiple alternatives have different values. Additionally, we also suggest flexibility and adaptability in the movement patterns in response to time constraints.

Abstract In goal-directed behavior, individuals are often required to plan and execute a movement with multiple competing reach targets simultaneously. The time constraint assigned to the target is an important factor that affect the initial movement planning, but the adjustments made to the starting behavior considering the time constraints specific to each target have not yet been clarified. The current study examined how humans adjusted their motor planning for double potential targets with independent time constraints under a go-before-you-know situation. The results revealed that the initial movements were modulated depending on the time constraints for potential targets. However, under tight time constraints, the performance in the double-target condition was lower than the single-target condition, which was a control condition implemented to estimate performance when one target is ignored. These results indicate that the initial movement for multiple potential targets with independent time constraints can be modified, but the planning is suboptimal.

Abstract Humans are often required to plan/execute movements in the presence of multiple motor targets simultaneously. Under such situations, it is widely confirmed that humans frequently initiate movements towards the weighted average direction of distinct motor plans toward each potential target. However, in situations where the potential targets change in a step-by-step manner, the strategy to proceed towards the weighted average direction at each time could be sub-optimal in light of the costs of the corrective response. Herein, we tested the sensorimotor strategy followed during a step-by-step reduction of potential goals. To test the hypothesis, we compared the corrective responses when the number of targets went from three to two, and when the number of targets went from three to one at the same time. As the results, weak corrections were confirmed when the number of targets was reduced from three to two. Moreover, the corrective responses when the number of targets went from three to two was smaller than the average behavior estimated from the corrective responses when the number of targets went from three to one at the same time. This pattern of corrective responses reflects the suppression of unnecessary corrections that generate noise and cost to the control system. These results suggest that the corrective responses are flexibly modulated depending on the necessity, and cannot be explained by weighted average behavior.

During goal-directed behaviors, individuals can be required to start a movement before deciding on the final goal. Previous studies have focused on the initial movement direction in situations involving multiple targets in different directions from the starting position and have shown that the movement is initiated in the average direction among the target directions. However, the previous studies only included situations with targets at equivalent distances, and the characteristics of motor planning in situations with multiple movement possibilities over different potential distances are unclear. In such situations, movement velocity is another important control variable. Furthermore, while previous studies examined situations with an uncertain motor target position, uncertainty can also exist in the effector position (e.g., body or tool locations). Therefore, we examined (1) whether the average output is confirmed in the initial movement velocity during execution in situations involving two potential movements with different distances. In addition, we examined (2) whether planning of the movement velocity can differ depending on the presence of uncertainty in the cursor or the target. In the main conditions, the participants were required to start a reaching movement with two potential movement distances; in the two-cursor condition, two cursors were presented before the start of the trial, and in the two-target condition, two targets were presented. As a control condition, a distance condition corresponding to each main condition was also performed. In the control condition, the initial movement velocity varied linearly with distance. Then, we tested whether the initial movement velocity in situations with two potential movement distances would follow the averaging output of the corresponding control condition. The results revealed that while the initial movement velocity in the two-target condition was slower than the averaging output, that in the two-cursor condition approached the averaging output. These results suggest that the velocity profile of the goal-directed movement is not simply averaged in a situation where two potential targets exist, and that there is a difference in the planning policy of the initial movement depending on whether the known uncertainty is for the movement goal or the effector.

Abstract Humans are often required to make decisions under time constraints and to adjust speed-accuracy tradeoff (SAT) based on time constraints. Previous studies have investigated how humans adjust SAT depending on the time discount rate of expected gain. Although the expected gain of actions can be determined by both gain and probability, only situations where gain decreases over time have been tested. Considering the effect of risk on decision-making, the difference in time discount factors may modulate the response strategies for SAT, since temporal changes in variance of possible outcomes differ when gain or probability decreases over time. Here, we investigated the response strategies for SAT under different time discount factors. Participants were required to select one of the two options with different initial values in situations where the expected gain of options declined over time by a linear decrease in gain or probability. Comparison of response strategies between conditions revealed that response times in the gain condition were longer than those in the probability condition, possibly due to risk-aversion. These findings indicate the existence of common rules underpinning sensorimotor and economic decision-making.

This study explored the mechanical factors that determine accuracy of a baseball pitching. In particular, we focused on the mechanical parameters at ball release, referred to as release parameters. The aim was to understand which parameter has the most deterministic influence on pitch location by measuring the release parameters during actual pitching and developing a simulation that predicts the pitch location from given release parameters. By comparing the fluctuation of the simulated pitch location when varying each release parameter, it was found that the elevation pitching angle and speed significantly influenced the vertical pitch location, and the azimuth pitching angle significantly influenced the horizontal pitch location. Moreover, a regression model was obtained to predict the pitch location, and it became clear that the significant predictors for the vertical pitch location were the elevation pitching angle, the speed, and spin axis, and those for the horizontal pitch location were the azimuth pitching angle, the spin axis, and horizontal release point. Therefore, it was suggested that the parameter most affecting pitch location weas pitching angle. On the other hand, multiple regression analyses revealed that the relation between release parameters varied between pitchers. The result is expected to contribute to an understanding of the mechanisms underlying accurate ball control skill in baseball pitching.

Humans often face situations requiring a decision about where to throw an object or when to respond to a stimulus under risk. Several behavioral studies have shown that such motor decisions can be suboptimal, which results from a cognitive bias toward risk-seeking behavior. However, brain regions involved in risk-attitude of motor decision-making remain unclear. Here, we investigated the role of the dorsolateral prefrontal cortex (DLPFC) in risky motor decisions using transcranial direct current stimulation (tDCS). The experiment comprised a selective timing task requiring participants to make a continuous decision about the timing of their response under the risk of no rewards. The participants performed this task twice in a day: before and while receiving either anodal stimulation over the right DLPFC with cathodal stimulation over the left DLPFC (20 min, 2 mA), cathodal stimulation over the right DLPFC with anodal stimulation over the left DLPFC, or sham stimulation. In line with previous studies, their strategies before the stimulation were biased toward risk-seeking. During anodal stimulation over right DLPFC with cathodal stimulation over left DLPFC, participants showed a more conservative strategy to avoid the risk of no rewards. The additional experiment confirmed that tDCS did not affect the ability of timing control regarding the time intervals at which they aimed to respond. These results suggest a potential role for the DLPFC in modulating action selection in motor decision-making under risk.

Numerous studies have shown the importance of metrical structure on beat perception and sensorimotor synchronization (SMS), which indicates why metrical structure has evolved as a widespread musical element. In the current study, we aimed to investigate the effect of metrical structure with or without accented sounds and the alignment of accent with flexion or extension movements on the stability of 1:2 SMS in rhythmic knee flexion-extension movement in upright stance (flexing the knee once every two sounds). Fourteen participants completed 1:2 rhythmic knee flexion-extension movements with a metronome beat that accelerated from 2 to 8 Hz (the frequency of the movement was 1–4 Hz). Three sound-movement conditions were provided: (1) combining the flexion phase with loud (accented) sound and the extension phase with soft (non-accented) sound, (2) the reverse combination, and (3) combining both movements with loud sound. ANOVA results showed that metrical structure with accented sounds stabilizes 1:2 SMS in the range of 3.5–7.8 Hz in terms of timing accuracy, and flexing on the accented sound is more globally stable (resistant to phase transition) than flexing on the non-accented sound. Furthermore, our results showed that metrical structure with accented sounds induces larger movement amplitude in the range of 4.6–7.8 Hz than does that without accented sounds. The present study demonstrated that metrical structure with accented sounds stabilizes SMS and induces larger movement amplitude in rhythmic knee flexion-extension movement in upright stance than does SMS with sequences without accents. In addition, we demonstrated that coordinating flexion movement with accented sound is more globally stable than coordinating extension movement with accented sound. Thus, whereas previous studies have revealed that metrical structure enhances the timing accuracy of SMS, the current study revealed that metrical structure enhances the global stability of SMS.

Previous studies have demonstrated that combining individuals with different social skills affects performance in rhythmic interpersonal motor coordination, with individuals with lower social skills, such as individuals with autism spectrum disorder or schizophrenia, being found to follow the actions of partners with higher social skills. In this study, we investigated whether this finding could be generalized among pairs of individuals without disability. To perform this, we applied an interpersonal motor coordination task that required participants to perform rhythmic movements featuring an interpersonal relative phase pattern of 90°. We did not assign the two roles (i.e., the preceding and following roles) to the participants, meaning they were forced to determine which roles to adopt by observing each other’s movements, without verbal communication. Individual social skills were measured using the autism-spectrum quotient (AQ). We found that pairs of participants with widely differing AQ scores performed better than did pairs with similar AQ scores. Most notably, the participants with higher AQ scores tended to precede their partners in the present task, which is the opposite result to that reported in previous studies. Our findings suggest that paring individuals without disability according to their social skills influences their interpersonal coordination performance in tasks wherein they must determine the preceding and following roles themselves.

In this study, we examined the degree of adaptability to new constraints after learning of a fundamental skill in juggling. Adaptation of sensorimotor synchronization with the various constraints is important for expertise. However, this adaptability may not be equivalent between coordination patterns which learners acquired in the previous learning process. In other words, there may be “asymmetric” adaptability among intrinsic patterns. Then, we examined the influence of intrinsic patterns on the adaptation of sensorimotor synchronization according to various temporal constraints. To set the adaptation task, experiment 1 was designed to examine the relationship between tempo and coordination pattern for expert jugglers. Based on experiment 1, juggling in accordance with the tempo change was performed as adaption task in experiment 2, and we compared the performances of the jugglers from the viewpoint of the intrinsic pattern. In experiment 1, participants performed juggling by adjusting catch timing to beep timing in ten conditions with the interval from 260 to 620 ms in steps of 40 ms. Results of experiment 1 presented that when the juggling tempo is fast, the coordination pattern with “rhythmic” frequency characteristics appeared. By contrast, when the tempo is slow, the coordination pattern with “discrete” frequency characteristics appeared. That is, jugglers should switch their coordination patterns when performing under various tempo conditions. In experiment 2, we compared the adaptability to perform juggling under temporal constraints among intermediate jugglers who have different intrinsic coordination patterns acquired through a previous learning process. The adaptation task required participants to adjust their catch timing to a gradually changing tempo. Participants performed juggling under two conditions: gradually ascending and descending tempo ranging from 300 to 600 ms. The results of experiment. 2 showed that participants who had a discrete pattern showed a significantly better adaptation than participants who had a rhythmic pattern. Furthermore, this result of adaptation was not related to juggling experience. This suggests that an intrinsic pattern characterized by different frequency characteristics has the different adaptability to sensorimotor synchronization tasks. Collectively, the degree of adaptability was dependent on the pattern acquired in the early stages of learning.

We investigated differences in trunk rotation patterns during baseball batting in eight skilled (collegiate level) players and nine unskilled novices using high-speed video cameras. The maximum angle during the backswing, angle at bat-ball impact, and angular displacement during the forward swing were analyzed for data on upper torso, pelvis, and torso-pelvis interaction (trunk twist) angles. We also noted movement variability in these angles over 10 trials, which was calculated as the standard deviation. The timing of the maximum angle during the backswing and variability was also analyzed. Statistical analysis revealed that angular displacements in the upper torso, pelvis, and torso-pelvis interaction were significantly larger in skilled players than in unskilled novices (p < 0.001, p < 0.001, and p < 0.05, respectively). The timing of the maximum pelvis angle during the backswing was significantly later in skilled players than in unskilled novices (p < 0.05). Movement variability in angular displacement during the forward swing and timing during the backswing were significantly greater in unskilled novices than skilled players. Although many previous studies reported the importance of angular velocity in trunk rotation during baseball batting, our results indicate that angular displacement and movement variability during trunk rotation are also key components for understanding the proficiency of skilled baseball players and unskilled novices.

Quickness of response and movement speed are required for achieving athletic success in a variety of sports, and are often lost in various movement disorders. Because cognitive processes such as anticipation, attention, and planning are required for preparation of a quick motor response, we first introduce recent neurophysiological studies that have revealed brain activities underlying the preparation for movement, with some neurophysiological applications to improve motor quickness. Moreover, recent developments in the dynamical analysis of complex movements allow us to understand precise mechanisms and principles underlying fast multi-joint and multi-limb movements. We introduce our current theories on the mathematical analysis of complex movement coordination called induced acceleration analysis. We propose that movements are subject to both instantaneous and cumulative effects, which combine to integrate the torque and acceleratory forces on multiple joints. We also discuss evidence that movement rate has important effects on the coordination patterns, acting as a control parameter that determines organization of movement patterns. These findings underscore the necessity of conducting research on the science of movement that is highly interdisciplinary, including the fields of physiology, biomechanics, neurosciences, and behavioral sciences not only for the enhancement of sports performance, but also for the facilitation of motor recovery and rehabilitation from neurological damage.

The current study investigated the rhythmic coordination between vocalization and whole-body movement. Previous studies have reported that spatiotemporal stability in rhythmic movement increases when coordinated with a rhythmic auditory stimulus or other effector in a stable coordination pattern. Therefore, the present study conducted two experiments to investigate (1) whether there is a stable coordination pattern between vocalization and whole-body movement and (2) whether a stable coordination pattern reduces variability in whole-body movement and vocalization. In Experiment 1, two coordination patterns between vocalizations and whole-body movement (hip, knee, and ankle joint flexion-on-the-voice vs. joint extension-on-the-voice) in a standing posture were explored at movement frequencies of 80, 130, and 180 beats per minute. At higher movement frequencies, the phase angle in the extension-on-the-voice condition deviated from the intended phase angle. However, the angle of the flexion-on-the-voice was maintained even when movement frequency increased. These results suggest that there was a stable coordination pattern in the flexion-on-the-voice condition. In Experiment 2, variability in whole-body movement and voice-onset intervals was compared between two conditions: one related to tasks performed in the flexion-on-the-voice coordination (coordination condition) that was a stable coordination pattern, and the other related to tasks performed independently (control condition). The results showed that variability in whole-body movement and voice-onset intervals was smaller in the coordination condition than in the control condition. Overall, the present study revealed mutual stabilization between rhythmic vocalization and whole-body movement via coordination within a stable pattern, suggesting that coupled action systems can act as a single functional unit or coordinative structure.