Visuomotor coordination with gaze, head and arm movements during table tennis forehand rallies.

The purpose of this study was to clarify the temporal coordination between gaze, head, and arm movements during forehand rallies in table tennis. Collegiate male table tennis players (n = 7) conducted forehand rallies at a constant tempo (100, 120, and 150 bpm) using a metronome. In each tempo condition, participants performed 30 strokes (a total of 90 strokes). Gaze, head, and dominant arm (shoulder, elbow, and wrist) movements were recorded with an eye-tracking device equipped with a Gyro sensor and a 3-D motion capture system. The results showed that the effect of head movements relative to gaze movements was significantly higher than that of eye movements in the three tempo conditions. Our results indicate that head movements are closely associated with gaze movements during rallies. Furthermore, cross-correlation coefficients (CCs) between head and arm movements were more than 0.96 (maximum coefficient: 0.99). In addition, head and arm movements were synchronized during rallies. Finally, CCs between gaze and arm movements were more than 0.74 (maximum coefficient: 0.99), indicating that gaze movements are temporally coordinated with arm movements. Taken together, head movements could play important roles not only in gaze tracking but also in the temporal coordination with arm movements during table tennis forehand rallies.

Properties of Gaze Strategies Based on Eye-Head Coordination in a Ball-Catching Task.

Visual motion information plays an important role in the control of movements in sports. Skilled ball players are thought to acquire accurate visual information by using an effective visual search strategy with eye and head movements. However, differences in catching ability and gaze movements due to sports experience and expertise have not been clarified. Therefore, the purpose of this study was to determine the characteristics of gaze strategies based on eye and head movements during a ball-catching task in athlete and novice groups. Participants were softball and tennis players and college students who were not experienced in ball sports (novice). They performed a one-handed catching task using a tennis ball-shooting machine, which was placed at 9 m in front of the participants, and two conditions were set depending on the height of the ball trajectory (high and low conditions). Their head and eye velocities were detected using a gyroscope and electrooculography (EOG) during the task. Our results showed that the upward head velocity and the downward eye velocity were lower in the softball group than in the tennis and novice groups. When the head was pitched upward, the downward eye velocity was induced from the vestibulo-ocular reflex (VOR) during ball catching. Therefore, it is suggested that skilled ball players have relatively stable head and eye movements, which may lead to an effective gaze strategy. An advantage of the stationary gaze in the softball group could be to acquire visual information about the surroundings other than the ball.

Prediction error in implicit adaptation during visually- and memory-guided reaching tasks.

Human movements are adjusted by motor adaptation in order to maintain their accuracy. There are two systems in motor adaptation, referred to as explicit or implicit adaptation. It has been suggested that the implicit adaptation is based on the prediction error and has been used in a number of motor adaptation studies. This study aimed to examine the effect of visual memory on prediction error in implicit visuomotor adaptation by comparing visually- and memory-guided reaching tasks. The visually-guided task is thought to be implicit learning based on prediction error, whereas the memory-guided task requires more cognitive processes. We observed the adaptation to visuomotor rotation feedback that is gradually rotated. We found that the adaptation and retention rates were higher in the visually-guided task than in the memory-guided task. Furthermore, the delta-band power obtained by electroencephalography (EEG) in the visually-guided task was increased immediately following the visual feedback, which indicates that the prediction error was larger in the visually-guided task. Our results show that the visuomotor adaptation is enhanced in the visually-guided task because the prediction error, which contributes update of the internal model, was more reliable than in the memory-guided task. Therefore, we suggest that the processing of the prediction error is affected by the task-type, which in turn affects the rate of the visuomotor adaptation.

The effect of eccentricity on visual motion prediction in peripheral vision.

The purpose of the current study was to clarify the effect of eccentricity on visual motion prediction using a time-to-contact (TTC) task. TTC indicates the predictive ability to accurately estimate the time-to-contact of a moving object based on visual motion perception. We also measured motion reaction time (motion RT) as an indicator of the speed of visual motion perception. The TTC task was to press a button when the moving target would arrive at the stationary goal. In the occluded condition, the target dot was occluded 500 ms before the time to contact. The motion RT task was to press a button as soon as the target moved. The visual targets were randomly presented at five different eccentricities (4°, 6°, 8°, 10°, 12°) and moved on a circular trajectory at a constant tangent velocity (8°/s) to keep the eccentricity constant. Our results showed that TTC in the occluded condition showed an earlier response as the eccentricity increased. Furthermore, the motion RT became longer as the eccentricity increased. Therefore, it is most likely that a slower speed perception in peripheral vision delays the perceived speed of motion onset and leads to an earlier response in the TTC task.

Importance of head movements in gaze tracking during table tennis forehand stroke.

The purpose of this study was to clarify the properties of gaze and head movements during forehand stroke in table tennis. Collegiate table tennis players (n = 12) conducted forehand strokes toward a ball launched by a skilled experimenter. A total of ten trials were conducted for the experimental task. Horizontal and vertical movements of the ball, gaze, head and eye were analyzed from the image recorded by an eye tracking device. The results showed that participants did not always keep their gaze and head position on the ball throughout the entire ball path. Our results indicate that table tennis players tend to gaze at the ball in the initial ball-tracking phase. Furthermore, there was a significant negative correlation between eye and head position especially in the vertical direction. This result suggests that horizontal VOR is suppressed more than vertical VOR in ball-tracking during table tennis forehand stroke. Finally, multiple regression analysis showed that the effect of head position to gaze position was significantly higher than that of eye position. This result indicates that gaze position during forehand stroke could be associated with head position rather than eye position. Taken together, head movements may play an important role in maintaining the ball in a constant egocentric direction in table tennis forehand stroke.

The effect of real-world and retinal motion on speed perception for motion in depth.

For motion in depth, even if the target moves at a constant speed in the real-world (physically), it would appear to be moving with acceleration on the retina. Therefore, the purpose of this study was to determine whether real-world and retinal motion affect speed perception in depth and to verify the influence of eye movements on both motion signals in judging speed in depth. We used a two-alternative forced-choice paradigm with two types of tasks. One stimulus moved at a constant speed in the real-world (world constant task) with three conditions: 80-60 cm (far), 60-40 cm (middle), and 40-20 cm (near) from the participant. The other stimulus moved at a constant speed on the retina (retinal constant task) with three conditions: 4-8 deg (far), 8-12 deg (middle), and 12-16 deg (near) as the vergence angle. The results showed that stimulus speed was perceived faster in the near condition than in the middle and far conditions for the world constant task, regardless of whether it was during fixation or convergence eye movements. In contrast, stimulus speed was perceived faster in the order of the far, middle, and near conditions for the retinal constant task. Our results indicate that speed perception of a visual target approaching the observer depends on real-world motion when the target position is relatively far from the observer. In contrast, retinal motion may influence speed perception when the target position is close to the observer. Our results also indicate that the effects of real-world and retinal motion on speed perception for motion in depth are similar with or without convergence eye movements. Therefore, it is suggested that when the visual target moves from far to near, the effects of real-world and retinal motion on speed perception are different depending on the initial target position.

Visual Strategies for Eye and Head Movements During Table Tennis Rallies.

The purpose of this study was to clarify the properties of visual strategies for gaze, eye, and head movements in skilled table tennis players during rallies. Collegiate expert and semi-expert table tennis players conducted forehand rallies at a constant tempo using a metronome. Two tempo conditions were used in the order of 130 and 150 bpm. Participants conducted a 20-stroke rally under each tempo condition. Horizontal and vertical angles between the gaze point and ball positions at the time the ball bounced (gaze-ball angle) were analyzed with the image that was recorded by an eye tracking device equipped with Gyro sensor. Eye and head movements during rallies were also recorded with the eye tracking device and Gyro sensor, respectively. The results showed that the gaze-ball angle of expert players was significantly larger than that of semi-expert players. This result indicates that expert players tended to keep their gaze position on the ball shorter than semi-expert players. We also found that eye movements of expert players were significantly smaller than that of semi-expert players. Furthermore, as the result of multiple regression analysis, the effect of eye movements on the gaze-ball angle was significantly higher than that of head movements. This result indicates that the gaze-ball angle during table tennis rallies could be associated with eye movements rather than head movements. Our findings suggest that the visual strategies used during table tennis rallies are different between expert and semi-expert players, even though they both have more than 10 years of experience.

The Effect of Target Velocity on the Fast Corrective Response during Reaching Movement.

Online motor control is often required to correct errors in rapid adjustments during reaching movements. It has been established that the initial arm trajectory during reaching is corrected by a target displacement. Since this corrective response occurs without perception of target perturbation, this is regarded as an automatic response. However, an object rarely "jumps" in daily life, rather it often "moves" as a chronological change of the position that causes visual motion. Therefore, the purpose of this study was to investigate whether the implicit visuomotor response is induced by target motion stimuli and to clarify the effects of target motion velocity on initial arm trajectory. Participants were asked to move a cursor from a start circle to a visual target. The target moved either leftward or rightward when the cursor passed 20 mm from the start circle. Four target velocities (10, 20, 30, 40 deg/s) were randomly presented. Our results showed that the initial velocity (first 50 ms) of the fast corrective response increased with the target velocity. Therefore, it is indicated that the fast corrective response is induced by the target motion stimulus with a short latency and its amplitude is dependent on the target velocity.

The influence of the motor command accuracy on the prediction error and the automatic corrective response.

The online control system allows for automatic corrective response to unexpected perturbation. This corrective response may involve a prediction error between the sensory prediction by the motor command and the actual feedback signal. Therefore, we attempted to investigate the effect of motor command accuracy on the automatic corrective response. Participants were asked to move a cursor displayed on a monitor and required to reach the center of a Gaussian blob target as accurately as possible for small and large Gaussian blob conditions. The accuracy of the motor command was manipulated by the size of the Gaussian blob. In half of the trials, a perturbation occurred in which the cursor position jumped 10 mm to either the left or right from the actual position, which induced an automatic corrective response. This corrective response was detected by the acceleration signal on the lateral axis. In addition, the prediction error was estimated by the amplitude of the N1 event-related potential (ERP) of the EEG signal. We found that the automatic response and N1 ERP were significantly larger in the small Gaussian blob conditions than in the large one. This result indicates that the automatic corrective response is affected by the certainty of the motor command manipulated by the Gaussian blob. Furthermore, the linear mixed-effect model (LME) indicated that the response is associated with the N1 ERP. Therefore, we suggest that the motor command accuracy affects the prediction error, which in turn modulates the automatic corrective response.

The effect of explicit cues on smooth pursuit termination.

Predictive deceleration of eye motion during smooth pursuit is induced by explicit cues indicating the timing of the visual target offset. The first aim of this study (experiment 1) was to determine whether the timing of the onset of cue-based predictive pursuit termination depends on spatial or temporal information using three target velocities. The second aim (experiment 2) was to examine whether an unexpected offset of the target affects the pursuit termination. We conducted a pursuit termination task where participants tracked a moving target and then stopped tracking after the target disappeared. The results of experiment 1 showed that the onset times of predictive eye deceleration were consistent regardless of target velocity, indicating that its timing is controlled by the temporal estimation, rather than the spatial distance between the target and cue positions. In experiment 2, we compared pursuit termination between the following two conditions. One condition did not present any cues (unknown condition), whereas a second condition included a same cue as experiment 1 but the target disappeared 500 ms before the timing indicated by the cue unpredictably (unexpected condition). As a result, the unexpected condition showed significant delays in the onset of eye deceleration, but no difference in the total time for completion of pursuit termination. Therefore, our findings suggest that the cue-based pursuit termination is controlled by the predictive pursuit system, and an unexpected offset of the target yields delays in the onset of eye deceleration, while does not affect the duration of pursuit termination.

The relationship between the implicit visuomotor control and the motor planning accuracy.

It has been well established that an implicit motor response can be elicited by a target perturbation or a visual background motion during a reaching movement. Computational studies have suggested that the mechanism of this response is based on the error signal between the efference copy and the actual sensory feedback. If the implicit motor response is based on the efference copy, the motor command accuracy would affect the amount of the modulation of the motor response. Therefore, the purpose of the current study was to investigate the relationship between the implicit motor response and the motor planning accuracy. We used a memory-guided reaching task and a manual following response (MFR) which is induced by visual grating motion. Participants performed reaching movements toward a memorized-target location with a beep cue which was presented 0 or 3 s after the target disappeared (0-s delay and 3-s delay conditions). Leftward or rightward visual grating motion was applied 400 ms after the cue. In addition, an event-related potential (ERP) was recorded during the reaching task, which reflects the motor command accuracy. Our results showed that the N170 ERP amplitude in the parietal electrodes and the MFR amplitude were significantly larger for the 3-s delay condition than the 0-s delay condition. These results suggest that the motor planning accuracy affects the amount of the implicit visuomotor response. Furthermore, there was a significant within-subjects correlation between the MFR and the N170 amplitude, which could corroborate the relationship between the implicit motor response and the motor planning accuracy.

Properties of fast vergence eye movements and horizontal saccades in athletes.

Visual information based on eye movements influences sports performance in 3-D space. The purpose of this study was to clarify the properties of fast vergence eye movements and horizontal saccades in athletes. Thirty-four college students were classified into three groups: twelve baseball players (BAS), ten track and field athletes (TRA) and twelve non-athletes (NON). The oculomotor tasks consisted of vergence eye movements (vergence task) including convergence and divergence, and horizontal saccades (saccade task). The participants made a rapid gaze shift toward a visual target. For the vergence task, the target was irradiated at 5 different vergence angles (3, 5, 10, 15, 20°) randomly. For the saccade task, the target was irradiated at 5 different saccade amplitudes (0, ±5, ±10°) randomly. The results showed that the peak eye velocity was higher in order of saccade, convergence, and divergence eye movements. The gain of convergence and saccades was higher than that of divergence. Furthermore, the latency of saccades was shorter than that of convergence and divergence. These results suggest that saccades and convergence are superior compared with divergence, and the dynamic property of convergence is partially analogous to horizontal saccades. The results of the comparison between the three groups showed that the latency of convergence was shorter for BAS than for NON. Therefore, different visual experience and baseball training could influence the gaze-shift dynamics during convergence eye movements.

Properties of smooth pursuit adaptation induced by theta motion.

Current study attempted to determine whether repeated smooth pursuit trials using theta motion, in which the directions of retinal image-motion and object-motion are opposed, yield pursuit adaptation. Adaptation trials consisted of 350 step-ramp trials using theta motion, and pre- and post-trials using first-order motion were conducted. As a result, initial acceleration in post-adaptation increased significantly than pre-adaptation trials. This was the case even though there was no adaptive change throughout adaptation (350 trials) using theta motion. Our results suggest that smooth pursuit could adapt to theta motion even with challenges associated with opposite retinal slip.

Properties of smooth pursuit and visual motion reaction time to second-order motion stimuli.

A large number of psychophysical and neurophysiological studies have demonstrated that smooth pursuit eye movements are tightly related to visual motion perception. This could be due to the fact that visual motion sensitive cortical areas such as meddle temporal (MT), medial superior temporal (MST) areas are involved in motion perception as well as pursuit initiation. Although the directional-discrimination and perceived target velocity tasks are used to evaluate visual motion perception, it is still uncertain whether the speed of visual motion perception, which is determined by visuomotor reaction time (RT) to a small target, is related to pursuit initiation. Therefore, we attempted to determine the relationship between pursuit latency/acceleration and the visual motion RT which was measured to the visual motion stimuli that moved leftward or rightward. The participants were instructed to fixate on a stationary target and press one of the buttons corresponding to the direction of target motion as soon as possible once the target starts to move. We applied five different visual motion stimuli including first- and second-order motion for smooth pursuit and visual motion RT tasks. It is well known that second-order motion induces lower retinal image motion, which elicits weaker responses in MT and MST compared to first-order motion stimuli. Our results showed that pursuit initiation including latency and initial eye acceleration were suppressed by second-order motion. In addition, second-order motion caused a delay in visual motion RT. The better performances in both pursuit initiation and visual motion RT were observed for first-order motion, whereas second-order (theta motion) induced remarkable deficits in both variables. Furthermore, significant Pearson's correlation and within-subjects correlation coefficients were obtained between visual motion RT and pursuit latency/acceleration. Our findings support the suggestion that there is a common neuronal pathway involved in both pursuit initiation and the speed of visual motion perception.

Influence of preceding muscle activity on movement-related cortical potential during superimposed ballistic contraction.

The purpose of current study was to clarify the influence of preceding muscle activity on the force production and movement-related cortical potential (MRCP) during superimposed ballistic contractions. The participants performed the ballistic force production at 40 % of maximum voluntary contraction (MVC) using the isometric abduction force of the metacarpophalangeal joint of the index finger. They were asked to match the peak of force curve with a horizontal target line displayed on the computer monitor. We compared the MRCP amplitude during force exertion detected from Fz, C4, C3, Cz and Pz electrodes during ballistic force production with (active condition) and without (resting condition) preceding muscle activity. The results showed that the MRCP amplitudes of Fz, C4, C3 and Cz electrodes were significantly smaller for the active condition than the resting condition. This was the case even though the peak force values during both conditions were identical. This result suggests that the facilitation of spinal motoneuron excitability by preceding muscle activity could reduce the required central motor command to produce the identical force level. In addition, we examined the MRCP amplitude during ballistic force production of the active condition without a visually displayed target. In this condition, the participants had to perform the force production based on aiming point of target force level (40 %MVC). As a result, the mean of peak force without a visual target was 54 %MVC, which overshot the aiming force level. However, the MRCP amplitudes of five electrodes during the 54 %MVC force production in the active condition were equivalent to the case of the 40 %MVC force production in the resting condition. These results suggest that the MRCP amplitude is consistent with participants' sense of effort involved in the force production, rather than the actual produced force level.

Influence of preceding muscle activity on perceptually guided force production during superimposed ballistic contraction.

Current study attempted to clarify whether preceding muscle activity influences the perceptually guided force production during superimposed ballistic contractions using isometric abduction of index finger. Subjects were verbally asked to produce ballistic force at requested percentages of their MVC with and without preceding muscle activity at 10% and 20%MVC. Our results showed that the ballistic force and EMG activity were increased significantly with preceding muscle activity at 20%MVC, but no change for 10%MVC. These results suggest that preceding muscle activity at sufficient intensity facilitates spinal motoneuron excitability, which could alter the relationship between the produced force and sense of effort.

The Influence of Contraction Types on the Relationship Between the Intended Force and the Actual Force.

It has been demonstrated that the intended force (subjective estimation of force) does not always match to actual force without external feedback. The purpose of this study was to compare the influence of ballistic and tonic contractions on the relationship between the intended and actual force. Subjects produced isometric force at requested percentages of their MVC (20, 40, 60 and 80%) based on subjective estimation of force under two conditions (tonic and ballistic conditions). The tonic condition was to maintain force production, whereas the ballistic condition was to produce force as fast as possible. As a result, the actual force amplitude, the coefficient of variance and EMG amplitude were larger under the ballistic contraction compared with the tonic condition, even the same intended force levels. These results suggest that different motor unit activity and control systems in the ballistic and tonic contractions could alter the relationship between the intended force and the actual force.

Asymmetric smooth pursuit eye movements and visual motion reaction time.

Smooth pursuit eye movements often show directional asymmetry in pursuit initiation or steady-state pursuit in both humans and monkeys. It has been demonstrated that the initial part of smooth pursuit is driven by visual motion related signals in cortical areas. Parietal cortex such as middle temporal (MT) and medial superior temporal (MST) areas are known to be involved in visual motion perception as well as pursuit initiation. Therefore, the purpose of this study is to determine whether directional asymmetry in pursuit initiation is associated with visual motion perception. We used a step-ramp paradigm to induce horizontal smooth pursuit eye movements and then tested visual motion reaction time (RT). Visual motion RT was measured to the visual motion stimuli that moved leftward or rightward, which is an important parameter of our sensory motor processing based on visual motion perception. Nineteen healthy male subjects participated in the study. We found that some of our subjects showed directional asymmetries in initial pursuit acceleration between the leftward and rightward directions, which were consistent with an asymmetric bias in visual motion RT. Therefore, our results suggest that asymmetric pursuit initiation is associated with, at least in part, a bias of visual motion perception. These results could be due to a common neuronal pathway involved in both pursuit initiation and visual motion RT.

Evaluation of pulse height control for rapid isometric contractions in college sprinters.

The ability of rapid force development is one of the important factors for improving physical performance. It has been known that rapid isometric force is controlled by a central motor program to maintain the rise time relatively constant independent of force amplitude (pulse height control). The advantage of using pulse height control is that it increases the rate of force with force amplitude. However, this strategy is believed to be applicable up to about 50-60% of maximal voluntary contractions (MVC). When the force level increases further, individuals often switch to pulse width control to increase the time to peak force. The aim of this study was to determine the force level (turning point) at which participants switch from pulse height control to pulse width control. This turning point was defined as the maximum force produced by pulse height control. We then attempted to examine whether this turning point is different among participants (control and sprinter groups). Therefore, participants were asked to perform isometric plantar flexions as fast as possible over a wide range of force levels (10-90%MVC). Our results showed that a turning point (%MVC) between two strategies was detected in all participants and the mean values were significantly higher in the sprinter group than that in the control group. Our results suggest that each participant has different limits of force level produced by pulse height control. The sprinter and control groups may use different control strategies for rapid force production at a higher force level.

Effects of Visual Error Timing on Smooth Pursuit Gain Adaptation in Humans.

Smooth pursuit (SP) is one of the precise oculomotor behaviors when tracking a moving object. Adaptation of SP is based on a visual-error driven motor learning process associated with predictable changes in the visual environment. Proper timing of a sensory signal is an important factor for adaptation of fine motor control. In this study, we investigated whether visual error timing affects SP gain adaptation. An adaptive change in SP gain is produced experimentally by repeated trials of a step-ramp tracking with 2 different velocities (double-velocity paradigm). The authors used the double-velocity paradigm where target speed changes 400 or 800 ms after the target onset. The results show that SP gain changed in a certain time window following adaptation. The authors suggest that SP adaptation shown in this study is associated with timing control mechanisms.