Manual Tracking Task Research Articles

Effects of input shaping on manual control of flexible and time-delayed systems.

The objective was to study the performance of a manual tracking task with system flexibility and time delays in the input channel and to examine the effects of input shaping the human operator's commands. It has long been known that low-frequency, lightly damped vibration hinders performance of a manually controlled system. Recently, input shaping has been shown to improve the performance of such systems in a compensatory-display tracking task. It is unknown if similar improvements are seen with pursuit-display tasks, or how the improvement changes when time delays are added to the system. A total of 18 novice participants performed a pursuit-view tracking experiment with a spring-centered joystick. Controlled elements included an integrator, an integrator with a lightly damped flexible mode, and an input-shaped integrator with a flexible mode. The input to these controlled elements was delayed between 0 and 1 s. Tracking performance was quantified by root mean square tracking error, and subjective difficulty was quantified by ratings on a Cooper-Harper scale. Performance was best with the undelayed integrator. Both time delay and flexibility degraded performance. Input shaping improved control of the flexible element, with a diminishing benefit as the time delay increased. Tracking error and subjective rating were significantly related. Some operators used a pulsive control strategy. Input shaping can improve the performance of a manually controlled system with flexibility, even when time delays are present. This study is useful to designers of human-controlled systems, especially those with problematic flexibility and/or time delays.

Children’s head movements and postural stability as a function of task

Manual dexterity and postural control develop throughout childhood, leading to changes in the synergistic relationships between head, hand and posture. But the postural developments that support complex manual task performance (i.e. beyond pointing and grasping) have not been examined in depth. We report two experiments in which we recorded head and posture data whilst participants simultaneously performed a visuomotor task. In Experiment 1, we explored the extent to which postural stability is affected by concurrently performing a visual and manual task whilst standing (a visual vs. manual-tracking task) in four age groups: 5-6 years (n = 8), 8-9 years (n = 10), 10-11 years (n = 7) and 19-21 years (n = 9). For visual tracking, the children's but not adult's postural movement increased relative to baseline with a larger effect for faster moving targets. In manual tracking, we found greater postural movement in children compared to adults. These data suggest predictive postural compensation mechanisms develop during childhood to improve stability whilst performing visuomotor tasks. Experiment 2 examined the extent to which posture is influenced by manual activity in three age groups of children [5-6 years (n = 14), 7-8 years (n = 25), and 9-10 years (n = 24)] when they were seated, given that many important tasks (e.g. handwriting) are learned and performed whilst seated. We found that postural stability varied in a principled manner as a function of task demands. Children exhibited increased stability when tracing a complex shape (which required less predictive postural adjustment) and decreased stability in an aiming task (which required movements that were more likely to perturb posture). These experiments shed light on the task-dependant relationships that exist between postural control mechanisms and the development of specific types of manual control.

Predictability is necessary for closed-loop visual feedback delay adaptation

In case of delayed visual feedback during visuomotor tasks, like in some sluggish computer games, humans can modulate their behavior to compensate for the delay. However, opinions on the nature of this compensation diverge. Some studies suggest that humans adapt to feedback delays with lasting changes in motor behavior (aftereffects) and a recalibration of time perception. Other studies have shown little or no evidence for such semipermanent recalibration in the temporal domain. We hypothesize that predictability of the reference signal (target to be tracked) is necessary for semipermanent delay adaptation. To test this hypothesis, we trained participants with a 200 ms visual feedback delay in a visually guided manual tracking task, varying the predictability of the reference signal between conditions, but keeping reference motion and feedback delay constant. In Experiment 1, we focused on motor behavior. Only training in the predictable condition brings about all of the adaptive changes and aftereffects expected from delay adaptation. In Experiment 2, we used a synchronization task to investigate perceived simultaneity (perceptuomotor learning). Supporting the hypothesis, participants recalibrated subjective visuomotor simultaneity only when trained in the predictable condition. Such a shift in perceived simultaneity was also observed in Experiment 3, using an interval estimation task. These results show that delay adaptation in motor control can modulate the perceived temporal alignment of vision and kinesthetically sensed movement. The coadaptation of motor prediction and target prediction (reference extrapolation) seems necessary for such genuine delay adaptation. This offers an explanation for divergent results in the literature.

Twists and Turns in Visuomotor Time Perception and Temporal Recalibration

In our perceptual world, voluntary actions (kinesthetically sensed) are temporally aligned with visual feedback about these actions. This requires compensation for existing latencies between the senses, for example due to neural processing. By training participants to the presence of a longer lag (e.g., Stetson et al., 2006) or shorter lag (Rohde & Ernst, 2013) between movement and visual feedback this subjective temporal alignment of vision and motion can also be recalibrated. Similar delay compensation and recalibrated have often been reported in multisensory time perception, including many cases where sensing is passive (e.g., audiovisual, visuotactile: Fujisaki et al., 1994; Keetels & Vroomen, 2008; Di Luca, Machulla, & Ernst, 2009). However, compared to these cases of passive sensing, active sensing, i.e., the processing of sensorimotor signals during intentional action, is influenced by additional factors: (1) the temporal asymmetry of agency and (2) the influence of action on sensation in the closed sensorimotor loop. We here summarize some of our recent results on temporal recalibration in sensorimotor control.For a visual event and an intentional movement event to be perceived as causally linked, the voluntary movement has to happen first (cause has to come before effect). This is not the case if sensory cues are sensed passively. To investigate the role of this temporal asymmetry in visuomotor time perception, we conducted a series of psychophysical experiments (Rohde & Ernst, 2013; Rohde, Greiner & Ernst,; Rohde, Scheller, & Ernst, 2012), where participants were presented with visual events that were timed around a voluntary button press. To be able to time visual stimuli also before the voluntary button press, we monitored participants finger movement and predicted the moment of the button press in real-time from the (stereotypical) movement trajectory. Perceptual judgments about relative visuomotor timing and perceived agency in response to visuomotor discrepancies were recorded.The window of perceived simultaneity resulting from relative timing judgments is asymmetrically skewed to tolerate larger visual lag temporal discrepancies than visual lead discrepancies (simultaneity judgments: Rohde, Scheller, & Ernst, 2012; interval estimation: Rohde, Greiner, & Ernst,). The sense of agency has been previously shown to distort our time perception of vision and intentional movement (Haggard, Clark, & Kalogeras, 2001), and these results suggest that the temporal asymmetry of agency appears to constrain the directionality of this effect. In line with this interpretation, we found that the temporal window of perceived agency is even more temporally asymmetrical (Rohde, Scheller, & Ernst, 2012). Furthermore, if participants’ perception of simultaneity is recalibrated, the window of perceived simultaneity is shrunk or extended on the side of visual lag stimuli only. The perceived timing of visual lead discrepancies that violate the underlying causal structure does not change (Rohde, Greiner, & Ernst,). The temporal asymmetry of intentional action distorts visuomotor time perception in a number of ways.Additionally, in closed-loop motor control tasks, sensory cues are partially determined by participants’ behavioral reactions to alterations in sensorimotor mappings. This implies that motor behavior can play a role in determining the outcome of perceptual recalibration in the closed loop. For instance, we found that target predictability in continuous manual tracking determines whether motor adaptation also involves perceptual temporal recalibration (Rohde, van Dam, & Ernst,). We trained participants in a visually guided manual tracking task with a 200ms visual feedback delay, varying the task predictability between conditions. Only training in the predictable condition led to a wide range of adaptation aftereffects in behavior as well as to perceptual temporal recalibration, which we measured by testing for transfer to synchronization and interval estimation tasks. This shows that the mere exposure to delayed visual feedback in manual tracking is not sufficient to induce temporal recalibration. Delay adaptation on the perceptual level requires specific behavioral adjustments to feedback delays that in turn depend on task predictability. This result can also explain controversies in the literature on closed-loop feedback delay adaptation: Some previous studies supported delay adaptation also on the level of perception (e.g., Cunningham, Billock, & Tsou, 2001; Cunningham et al., 2001a), others report little or no evidence for delay adaptation beyond a mere stabilization of motor strategy (e.g., Miall & Jackson, 2006).These two strands of evidence provide examples of how sensorimotor time perception in the context of intentional action is modulated by additional factors not usually deemed relevant in the study of multisensory temporal processing: the temporal order of modalities, the sense of agency, and the perceptual consequences of motor learning. This distinguishes sensorimotor time perception from multisensory time perception scenarios where stimuli are passively sensed.

Great expectations: Top-down attention modulates the costs of clutter and eccentricity.

An experiment and modeling effort examined interactions between bottom-up and top-down attentional control in visual alert detection. Participants performed a manual tracking task while monitoring peripheral display channels for alerts of varying salience, eccentricity, and spatial expectancy. Spatial expectancy modulated the influence of salience and eccentricity; alerts in low-probability locations engendered higher miss rates, longer detection times, and larger costs of visual clutter and eccentricity, indicating that top-down attentional control offset the costs of poor bottom-up stimulus quality. Data were compared to the predictions of a computational model of scanning and noticing that incorporates bottom-up and top-down sources of attentional control. The model accounted well for the overall pattern of miss rates and response times, predicting each of the observed main effects and interactions. Empirical results suggest that designers should expect the costs of poor bottom-up visibility to be greater for low expectancy signals, and that the placement of alerts within a display should be determined based on the combination of alert expectancy and response priority. Model fits suggest that the current model can serve as a useful tool for exploring a design space as a precursor to empirical data collection and for generating hypotheses for future experiments.

An External Focus of Attention Enhances Manual Tracking of Occluded and Visible Targets

The present study investigated the enhancement effects of an external focus of attention (FOA) in the context of a manual tracking task, in which participants tracked both visible and occluded targets. Three conditions were compared, which manipulated the distance of the FOA from the participant as well as the external/internal dimension. As expected, an external FOA resulted in lower tracking errors than an internal FOA. In addition, analyses of participants’ movement patterns revealed a systematic shift toward higher-frequency movements in the external FOA condition, consistent with the idea that an external FOA exploits the natural movement dynamics available during skilled action. Finally, target visibility did not influence the effect of focused attention on tracking performance, which provides evidence for the proposal that the mechanisms that underlie FOA do not depend directly on vision.

Simultaneous reconstruction of continuous hand movements from primary motor and posterior parietal cortex

Primary motor cortex (MI) and parietal area PE both participate in cortical control of reaching actions, but few studies have been able to directly compare the form of kinematic encoding in the two areas simultaneously during hand tracking movements. To directly compare kinematic coding properties in these two areas under identical behavioral conditions, we recorded simultaneously from two chronically implanted multielectrode arrays in areas MI and PE (or areas 2/5) during performance of a continuous manual tracking task. Monkeys manually pursued a continuously moving target that followed a series of straight-line movement segments, arranged in a sequence where the direction (but not length) of the upcoming segment varied unpredictably as each new segment appeared. Based on recordings from populations of MI (31-143 units) and PE (22-87 units), we compared hand position and velocity reconstructions based on linear filters. We successfully reconstructed hand position and velocity from area PE (mean r (2)=0.751 for position reconstruction, r (2)=0.614 for velocity), demonstrating trajectory reconstruction from each area. Combing these populations provided no reconstruction improvements, suggesting that kinematic representations in MI and PE encode overlapping hand movement information, rather than complementary or unique representations. These overlapping representations may reflect the areas' common engagement in a sensorimotor feedback loop for error signals and movement goals, as required by a task with continuous, time-evolving demands and feedback. The similarity of information in both areas suggests that either area might provide a suitable target to obtain control signals for brain computer interface applications.

Long Latency Electromyographic Response Induced by Transcranial Magnetic Stimulation over the Cerebellum Preferentially Appears During Continuous Visually Guided Manual Tracking Task

We investigated whether long latency motor response induced by transcranial magnetic stimulation over the cerebellum (C-TMS) preferentially appears during a continuous visually guided manual tracking task, and whether it originates in a concomitantly evoked neck twitch. C-TMS or magnetic stimulation over the neck (N-MS) was delivered during one of four tasks: a continuous or discrete visually guided manual tracking task, or phasic or tonic contraction of the first dorsal interosseous muscle. The probability of long latency fluctuation of index finger movement induced by C-TMS was not significantly different from that induced by N-MS, but the probability of long latency fluctuation induced by C-TMS and that induced by N-MS was significantly higher than that induced by sham TMS during all the tasks. The probability of long latency electromyographic response in the first dorsal interosseous muscle induced by C-TMS was significantly higher than that induced by N-MS and that induced by sham TMS during the continuous visually guided manual tracking task. Such significant differences were not present during the other tasks. Long latency electromyographic response induced by C-TMS preferentially appears during the continuous visually guided manual tracking task and is not explained by a concomitantly evoked neck twitch.

Effects of Input Shaping on Manual Tracking with Flexible and Time-Delayed System Dynamics

Manual tracking tasks are more difficult when the system used for tracking has flexibility and time delays. This paper uses a set of operator experiments to quantitatively examine how system flexibility and time delays degrade manual tracking. Additionally, it investigates the effects of adding input shaping to the system. Performance is quantified by root-mean-squared tracking error and subjective rating of difficulty.

Age-related decline of peripheral visual processing: the role of eye movements

Earlier work suggests that the area of space from which useful visual information can be extracted (useful field of view, UFoV) shrinks in old age. We investigated whether this shrinkage, documented previously with a visual search task, extends to a bimanual tracking task. Young and elderly subjects executed two concurrent tracking tasks with their right and left arms. The separation between tracking displays varied from 3 to 35 cm. Subjects were asked to fixate straight ahead (condition FIX) or were free to move their eyes (condition FREE). Eye position was registered. In FREE, young subjects tracked equally well at all display separations. Elderly subjects produced higher tracking errors, and the difference between age groups increased with display separation. Eye movements were comparable across age groups. In FIX, elderly and young subjects tracked less well at large display separations. Seniors again produced higher tracking errors in FIX, but the difference between age groups did not increase reliably with display separation. However, older subjects produced a substantial number of illicit saccades, and when the effect of those saccades was factored out, the difference between young and older subjects’ tracking did increase significantly with display separation in FIX. We conclude that the age-related shrinkage of UFoV, previously documented with a visual search task, is observable with a manual tracking task as well. Older subjects seem to partly compensate their deficit by illicit saccades. Since the deficit is similar in both conditions, it may be located downstream from the convergence of retinal and oculomotor signals.

Effect of low frequency motion on the performance of a dynamic manual tracking task

The assessment of wind-induced motion plays an important role in the development and design of the majority of today's structures that push the limits of engineering knowledge. A vital part of the design is the prediction of wind-induced tall building motion and the assessment of its effects on occupant comfort. Little of the research that has led to the development of the various international standards for occupant comfort criteria have considered the effects of the low-frequency motion on task performance and interference with building occupants' daily activities. It has only recently become more widely recognized that it is no longer reasonable to assume that the level of motion that a tall building undergoes in a windstorm will fall below an occupants' level of perception and little is known about how this motion perception could also impact on task performance. Experimental research was conducted to evaluate the performance of individuals engaged in a manual tracking task while subjected to low level vibration in the frequency range of 0.125 Hz-0.50 Hz. The investigations were carried out under narrow-band random vibration with accelerations ranging from 2 milli-g to 30 milli-g (where 1 milli-g = 0.0098 <TEX>$m/s^2$</TEX>) and included a control condition. The frequencies and accelerations simulated are representative of the level of motion expected to occur in a tall building (heights in the range of 100 m -350 m) once every few months to once every few years. Performance of the test subjects with and without vibration was determined for 15 separate test conditions and evaluated in terms of time taken to complete a task and accuracy per trial. Overall, the performance under the vibration conditions did not vary significantly from that of the control condition, nor was there a statistically significant degradation or improvement trend in performance ability as a function of increasing frequency or acceleration.

Switched manual pursuit tracking to measure motor performance in Parkinson's disease

Control theoretic measures are proposed to assess motor performance in Parkinson's disease (PD), a neuro-degenerative disorder that impairs motor skills, speech, and aspects of cognition. Ten normal and 14 PD subjects performed a series of manual pursuit tracking tasks: three tasks were first performed separately, then as a merged sequence with sudden, unenunciated task changes. The tasks differed in whether the tracking errors appeared amplified, attenuated or unaltered. From the discrete block experiments, subject- and task-specific second-order, linear time invariant models were derived, with the trajectory subjects are asked to track as input and the subject's motor response as output. Multiple model adaptive estimation was employed on the merged sequences to determine whether, and with what delay, each subject modified their performance after a task change. Although all normal subjects detected the task change, less than one-third of PD subjects did (and with longer delay). Further, those PD subjects who detected the task change had estimators with higher damping ratio than those PD subjects who did not. Since cerebellar structures may affect damping ratio, and the basal ganglia are often associated with switching behaviour, the proposed method provides a comprehensive assessment of motor structures that may be affected in PD.

Effects of Galvanic vestibular stimulation on cognitive function

Although imaging studies suggest activation of cortical areas by vestibular input, there is little evidence of an adverse effect of non-veridical vestibular input on cognitive function. To test the hypothesis that degraded vestibular afferent input adversely affects cognition, we compared performance on a cognitive test battery in a group undergoing suprathreshold bilateral bipolar Galvanic vestibular stimulation (GVS) with a control group receiving no GVS or subthreshold stimulation. The battery consisted of six cognitive tests as follows: reaction time, dual tasking, Stroop, mental rotation, perspective-taking and matching-to-sample, as well as a simple visuomotor (manual tracking) task. Subjects performed the test battery before, during and after suprathreshold GVS exposure or subthreshold stimulation. Suprathreshold GVS significantly increased error rate for the match-to-sample and perspective-taking tasks relative to the subthreshold group, demonstrating a negative effect of non-veridical vestibular input in these specific cognitive tasks. Reaction time, dual tasking, mental rotation and manual tracking were unaffected by GVS exposure. The adverse effect of suprathreshold GVS on perspective taking but not mental rotation is consistent with imaging studies, which have demonstrated that egocentric mental transformations (perspective taking) occur primarily in cortical areas that receive vestibular input (the parietal-temporal junction and superior parietal lobule), whereas object-based transformations (mental rotation) occur in the frontoparietal region. The increased error rate during the match-to-sample task is likely due to interference with hippocampal processing related to spatial memory, as suggested by imaging studies on vestibular patients.

Performance on a manual tracking task differentiates individuals at risk of developing carpal tunnel syndrome from those not at risk

Introduction The purpose of this study was to determine whether sensorimotor abnormalities are detectable in asymptomatic individuals deemed at risk of developing carpal tunnel syndrome (CTS) Methods Seventeen individuals deemed at risk of developing CTS and 16 asymptomatic individuals deemed to be at minimal risk of developing CTS participated. Nerve conduction velocity, two-point discrimination ability, pressure acuity, Purdue Pegboard Test performance and tracking error and tracking variance on a manual tracking task performed at two different speeds were measured in all participants and compared between the groups. Results None of the measures of nerve conduction, sensory perception, or Purdue Pegboard task performance were different between the groups. The error in the manual tracking tasks was significantly different between the groups, where the at-risk group demonstrated more error than the control group. Conclusion These results suggest that manual tracking tasks may be useful in the identification of those individuals at risk of developing CTS before they develop any measurable sensorimotor impairment.

Understanding reliance on automation: effects of error type, error distribution, age and experience

An obstacle detection task supported by ‘imperfect’ automation was used with the goal of understanding the effects of automation error types and age on automation reliance. Sixty younger and sixty older adults interacted with a multi-task simulation of an agricultural vehicle (i.e. a virtual harvesting combine). The simulator included an obstacle detection task and a fully manual tracking task. A micro-level analysis provided insight into the way reliance patterns change over time. The results indicated that there are distinct patterns of reliance that develop as a function of error type. A prevalence of automation false alarms led participants to under-rely on the automation during alarm states while over-relying on it during non-alarm states. Conversely, a prevalence of automation misses led participants to over-rely on automated alarms and under-rely on the automation during non-alarm states. Older adults adjusted their behaviour according to the characteristics of the automation similar to younger adults, although it took them longer to do so. The results of this study suggest that the relationship between automation reliability and reliance depends on the prevalence of specific errors and on the state of the system. Understanding the effects of automation detection criterion settings on human–automation interaction can help designers of automated systems to make predictions about human behaviour and system performance as a function of the characteristics of the automation.

Interactions Among Target Salience, Eccentricity, Target Expectancy and Workload in an Alert Detection Task

Attentional behavior in complex visual workspaces is driven by the physical and temporal characteristics of the display, the goals and knowledge of the operator, and task demands. Accordingly, to develop effective displays, designers must understand how these factors interact to influence attentional allocation within the display and the detectability of critical alerts. In the current study, participants performed a central highway-in-the-sky (HITS) manual tracking task and a peripheral alert detection task concurrently while alert eccentricity, salience, expectancy, and central task workload were manipulated. Eccentricity and expectancy effects were observed in both hit rates and response times (RTs). RT evinced interactions of salience with both eccentricity and expectancy, indicating that the absence of dynamic distractors allowed for more rapid detection of near alerts and more effective use of top-down attentional guidance in the detection of targets in high expectancy locations. Effects also manife...

Representation of limb kinematics in Purkinje cell simple spike discharge is conserved across multiple tasks

Encoding of movement kinematics in Purkinje cell simple spike discharge has important implications for hypotheses of cerebellar cortical function. Several outstanding questions remain regarding representation of these kinematic signals. It is uncertain whether kinematic encoding occurs in unpredictable, feedback-dependent tasks or kinematic signals are conserved across tasks. Additionally, there is a need to understand the signals encoded in the instantaneous discharge of single cells without averaging across trials or time. To address these questions, this study recorded Purkinje cell firing in monkeys trained to perform a manual random tracking task in addition to circular tracking and center-out reach. Random tracking provides for extensive coverage of kinematic workspaces. Direction and speed errors are significantly greater during random than circular tracking. Cross-correlation analyses comparing hand and target velocity profiles show that hand velocity lags target velocity during random tracking. Correlations between simple spike firing from 120 Purkinje cells and hand position, velocity, and speed were evaluated with linear regression models including a time constant, τ, as a measure of the firing lead/lag relative to the kinematic parameters. Across the population, velocity accounts for the majority of simple spike firing variability (63 ± 30% of R(adj)(2)), followed by position (28 ± 24% of R(adj)(2)) and speed (11 ± 19% of R(adj)(2)). Simple spike firing often leads hand kinematics. Comparison of regression models based on averaged vs. nonaveraged firing and kinematics reveals lower R(adj)(2) values for nonaveraged data; however, regression coefficients and τ values are highly similar. Finally, for most cells, model coefficients generated from random tracking accurately estimate simple spike firing in either circular tracking or center-out reach. These findings imply that the cerebellum controls movement kinematics, consistent with a forward internal model that predicts upcoming limb kinematics.

Assessing Manual Pursuit Tracking in Parkinson’s Disease Via Linear Dynamical Systems

Quantitative assessment of motor performance is important for diseases of motor control, such as Parkinson's disease (PD). Manual tracking tasks are well suited for motor assessment, as they can be performed concomitantly with brain mapping techniques. Here we propose utilizing second-order linear dynamical systems to assess manual pursuit tracking performance. With the desired trajectory as the input, and the subject's actual motor response as the output, a linear model characterized by natural frequency and damping ratio is identified for each subject. We applied this method to 10 PD subjects (on and off L: -dopa medication) and 10 normal subjects performing a multi-frequency sinusoidal tracking task. Model parameters were more sensitive than overall tracking errors in determining significant differences between groups. The effect of L: -dopa medication was to reduce the damping ratio and make the range in natural frequency across individuals approach that of normal subjects. We interpret the changes in damping ratio and natural frequency as possibly related to suppression of compensatory cerebellar activity and/or improvement of motor program selection, and the changes in natural frequency as an implicit strategy to maintain settling time in the face of reduce damping ratio. Our results suggest that simple linear dynamical system models can be a powerful method to assess tracking performance in Parkinson's disease because of the additional insight they can provide into neurological processes.

An MEG investigation of the neural mechanisms subserving complex visuomotor coordination

Fifteen human participants performed a manual and ocular tracking task with a continuously and unpredictably moving visual target, while magnetoencephalography (MEG) signals were recorded. Three-dimensional source reconstructions were generated from the MEG signals, using synthetic aperture magnetometry (SAM). The SAM images indicated main effects of alpha band (8–15 Hz) and beta band (15–30 Hz) source power decreases, for manual tracking in the sensorimotor and parietal cortices, and for ocular tracking in the parietal and occipital cortices. Additionally, the manual tracking task evoked a clear, contralateral motor cortex response in the form of high gamma band (60–90 Hz) source power increases. Time-frequency spectrograms revealed the induced gamma band power increases were sustained for the duration of each ten second trial demonstrating these oscillations are not simply transients associated with movement onset. The onset of the gamma band response was characterised by higher initial onset power and frequency but no correlations were observed between oscillatory power and successful tracking performance.

Cerebellar TMS Evokes a Long Latency Motor Response in the Hand during a Visually Guided Manual Tracking Task

Previous studies showed that transcranial magnetic stimulation (TMS) to the cerebellum evokes a long latency motor response in the soleus muscle during a postural task. The cerebellum is activated not only during postural tasks but also during motor tasks for which eye-hand coordination is required. The purpose of this study was to investigate whether TMS over the cerebellum evokes long latency motor responses in the hand during a visually guided manual tracking task. Eight healthy humans tracked an oscillatory moving target with the right index finger or pointed the finger at a stationary target, and TMS was delivered to the scalp over the cerebellum during the motor tasks. Trials with sham TMS were inserted between the trials with cerebellar TMS. The trajectory of finger movement fluctuated 92ms after cerebellar TMS with a 24% probability during tracking of a moving target. The fluctuation was preceded by an electromyographic burst in the first dorsal interosseous muscle starting at 65ms after TMS. The probability of fluctuation evoked by cerebellar TMS was significantly larger than that evoked by sham TMS during tracking of a moving target. This significant difference was absent in trials during which subjects pointed their index finger at a stationary target. These findings indicate that cerebellar TMS evokes a long latency motor response during a visually guided manual tracking task. The long latency motor response may be related to cerebellar activity associated with eye-hand coordination or to the detection of and correction for visuomotor errors.