Pacing Signal Research Articles

ECG classification using morphological features derived from symbolic dynamics

The aim of this study is to estimate how far the symbolic analysis helps to characterize the nonlinear properties of Electrocardiogram (ECG) signals and thereby discriminate between normal and arrhythmia signals. Differences were found in the properties of the symbol sequence histogram of the resulting patterns and complexity measures of symbol sequences among the five different classes, namely normal, left bundle branch block (LBBB), right bundle branch block (RBBB), premature-ventricular contraction (PVC) and paced signals. The efficacy of the symbolic analysis features is also shown through classification achieved through the neural network which exhibits an average accuracy that exceeds 93.5%.

The Build-Up Course of Visuo-Motor and Audio-Motor Temporal Recalibration

The sensorimotor timing is recalibrated after a brief exposure to a delayed feedback of voluntary actions (temporal recalibration effect: TRE) (Heron et al., 2009; Stetson et al., 2006; Sugano et al., 2010). We introduce a new paradigm, namely ‘synchronous tapping’ (ST) which allows us to investigate how the TRE builds up during adaptation. In each experimental trial, participants were repeatedly exposed to a constant lag (∼150 ms) between their voluntary action (pressing a mouse) and a feedback stimulus (a visual flash / an auditory click) 10 times. Immediately after that, they performed a ST task with the same stimulus as a pace signal (7 flashes / clicks). A subjective ‘no-delay condition’ (∼50 ms) served as control. The TRE manifested itself as a change in the tap-stimulus asynchrony that compensated the exposed lag (eg, after lag adaptation, the tap preceded the stimulus more than in control) and built up quickly (∼3–6 trials, ∼23–45 sec) in both the visuo- and audio-motor domain. The audio-motor TRE...

The role of temporal prediction abilities in interpersonal sensorimotor synchronization

Musical ensemble performance is a form of joint action that requires highly precise yet flexible interpersonal action coordination. To maintain synchrony during expressive passages that contain tempo variations, musicians presumably anticipate the sounds that will be produced by their co-performers. Our previous studies revealed that individuals differ in their ability to predict upcoming event timing when finger tapping in synchrony with tempo-changing pacing signals (i.e., the degree to which inter-tap intervals match vs. lag behind inter-onset intervals in the pacing signal varies between individuals). The current study examines the influence of these individual differences on synchronization performance in a dyadic tapping task. In addition, the stability of individual prediction tendencies across time is tested. Individuals with high or low prediction tendencies were invited to participate in two experimental sessions. In both sessions, participants were asked (1) to tap alone with a tempo-changing pacing signal and (2) to tap synchronously in dyads comprising individuals with similar or different prediction tendencies. Results indicated that individual differences in prediction tendencies were stable over several months and played a significant role in dyadic synchronization. Dyads composed of two high-predicting individuals tapped with higher accuracy and less variability than low-predicting dyads, while mixed dyads were intermediate. Prediction tendencies explained variance in dyadic synchronization performance over and above individual synchronization ability. These findings suggest that individual differences in temporal prediction ability may potentially mediate the interaction of cognitive, motor, and social processes underlying musical joint action.

Intentional control and biomechanical exploitation in preparatory handwriting

In this study it was investigated how primary school children perform a graphomotor task which required them to simultaneously achieve multiple movement goals. Thirty-four 1st-grade primary school children were asked to produce with an electronic ink pen loop patterns varying in height (3, 6, 9 and 12 mm) on preprinted sheets of paper attached to a digitizer tablet. The task was paced by means of an acoustic signal of either 1, 2 or 3 Hz. The children were instructed to attain both the imposed amplitude and frequency. By focusing on how local parameter errors changed from one movement to the next, exploitation of biomechanics when the children respected the inverse relationship between movement amplitude and frequency was distinguished from deliberate, cognitive control when the children succeeded in overriding the inverse relationship between movement amplitude and frequency. The results show that children, like adults, exploit biomechanics to a considerable extent. Coupling strength between the acoustic pacing signal and the pen-tip movements increased with age, whereas the temporal errors decreased. The study shows that preparatory writers can pursue multiple movement goals simultaneously at lower speeds but at higher speeds their capacity to do so is reduced.

The impact of basal ganglia lesions on sensorimotor synchronization, spontaneous motor tempo, and the detection of tempo changes

The basal ganglia (BG) are part of extensive subcortico-cortical circuits that are involved in a variety of motor and non-motor cognitive functions. Accumulating evidence suggests that one specific function that engages the BG and associated cortico-striato-thalamo-cortical circuitry is temporal processing, i.e., the mechanisms that underlie the encoding, decoding and evaluation of temporal relations or temporal structure. In the current study we investigated the interplay of two processes that require precise representations of temporal structure, namely the perception of an auditory pacing signal and manual motor production by means of finger tapping in a sensorimotor synchronization task. Patients with focal lesions of the BG and healthy control participants were asked to align finger taps to tone sequences that either did or did not contain a tempo acceleration or tempo deceleration at a predefined position, and to continue tapping at the final tempo after the pacing sequence had ceased. Performance in this adaptive synchronization-continuation paradigm differed between the two groups. Selective damage to the BG affected the abilities to detect tempo changes and to perform attention-dependent error correction, particularly in response to tempo decelerations. An additional assessment of preferred spontaneous, i.e., unpaced but regular, production rates yielded more heterogeneous results in the patient group. Together these findings provide evidence for less efficient processing in the perception and the production of temporal structure in patients with focal BG lesions. The results also support the functional role of the BG system in attention-dependent temporal processing.

Effects of feedback from active and passive body parts on spatial and temporal parameters in sensorimotor synchronization

Previous research on sensorimotor synchronization has manipulated the somatosensory information received from the tapping finger to investigate how feedback from an active effector affects temporal coordination. The current study explored the role of feedback from passive body parts in the regulation of spatiotemporal motor control parameters by employing a task that required finger tapping on one's own skin at anatomical locations of varying tactile sensitivity. A motion capture system recorded participants' movements as they synchronized with an auditory pacing signal by tapping with the right index finger on either their left index fingertip (Finger/Finger) or forearm (Finger/Forearm). Results indicated that tap timing was more variable, and movement amplitude was larger and more variable, when tapping on the finger than when tapping on the less sensitive forearm. Finger/Finger tapping may be impaired relative to Finger/Forearm tapping due to ambiguity arising through overlap in neural activity associated with tactile feedback from the active and the passive limb in the former. To compensate, the control system may strengthen the assignment of tap-related feedback to the active finger by generating correlated noise in movement kinematics and tap dynamics.

Auditory imagery shapes movement timing and kinematics: Evidence from a musical task.

The role of anticipatory auditory imagery in music-like sequential action was investigated by examining timing accuracy and kinematics using a motion capture system. Musicians responded to metronomic pacing signals by producing three unpaced taps on three vertically aligned keys at the given tempo. Taps triggered tones in two out of three blocked feedback conditions, where key-to-tone mappings were compatible or incompatible in terms of spatial and pitch height. Results indicate that, while timing was most accurate without tones, movements were smaller in amplitude and less forceful (i.e., acceleration prior to impact was lowest) when tones were present. Moreover, timing was more accurate and movements were less forceful with compatible than with incompatible auditory feedback. Observing these effects at the first tap (before tone onset) suggests that anticipatory auditory imagery modulates the temporal kinematics of regularly timed auditory action sequences, like those found in music. Such cross-modal ideomotor processes may function to facilitate planning efficiency and biomechanical economy in voluntary action.

How voluntary actions modulate time perception

Distortions of time perception are generally explained either by variations in the rate of pacing signals of an “internal clock”, or by lag-adaptation mechanisms that recalibrate the perceived time of one event relative to another. This study compares these accounts directly for one temporal illusion: the subjective compression of the interval between voluntary actions and their effects, known as ‘intentional binding’. Participants discriminated whether two cutaneous stimuli presented after voluntary or passive movements were simultaneous or successive. In other trials, they judged the temporal interval between their movement and an ensuing tone. Temporal discrimination was impaired following voluntary movements compared to passive movements early in the action-tone interval. In a control experiment, active movements without subsequent tones produced no impairment in temporal discrimination. These results suggest that voluntary actions transiently slow down an internal clock during the action-effect interval. This in turn leads to intentional binding, and links the effects of voluntary actions to the self.

Modality specific functional interaction in sensorimotor synchronization

Movement execution strongly relies on precise sensorimotor synchronization. In a finger-tapping task that requires subjects to synchronize their finger taps to regular pacing signal synchronization accuracy varies with respect to pacing signal's modality. This study aimed at elucidating functional brain dynamics associated with modality specific behavioral synchronization accuracy. To this end, 10 right-handed subjects performed a finger-tapping task with respect to regular auditory and visual pacing, respectively, whereas neuromagnetic activity was recorded using a 122-channel whole-head neuromagnetometer. Visual pacing was associated with significantly reduced tap-to-pacer asynchrony and increased intertap variability as compared to auditory pacing. The brain dynamics associated with task execution were analyzed using the frequency domain beamformer approach dynamic imaging of coherent sources (DICS). Both tasks were shown to be associated with comparable networks. However, during visual pacing involvement of the ventral premotor cortex (PMv) was shown, whereas during auditory pacing the dorsal premotor cortex (PMd) was concerned with task execution. Synchronization with respect to visual pacing was associated with significantly increased functional interaction between thalamus and PMv at beta frequency as compared to functional interplay between thalamus and PMd during auditory pacing. Auditory synchronization was associated with increased functional interaction between left superior temporal gyrus and PMd at alpha frequency. Furthermore, functional interaction between thalamus and premotor cortex at beta frequency was significantly correlated with synchronization accuracy. All in all the present data suggest that modality specific synchronization differences are associated with frequency and connectivity specific changes of functional interaction in distinct brain networks.

Evidence for Anticipatory Motor Control within a Cerebello-Diencephalic-Parietal Network

The posterior parietal cortex and the cerebellum are assumed to contribute to anticipatory motor control. Thus, it is reasonable that these areas act as a functional unit. To identify a neural signature of anticipatory motor control, 11 healthy volunteers performed a bimanual finger-tapping task with respect to isochronous (i.e., regular) and randomized (i.e., irregular) auditory pacing. Neuromagnetic activity was recorded using a 122-channel whole-head neuromagnetometer. Functional interaction between spatially distributed brain areas was determined by measures of tap-related phase synchronization. Assuming that (i) the cerebellum predicts sensory events by an internal model and (ii) the PPC maintains this prediction, we hypothesized that functional interaction between both structures varies depending on the predictability of the pacing signal. During isochronous pacing, functional connectivity within a cerebello-diencephalic-parietal network before tap onset was evident, suggesting anticipatory motor control. During randomized pacing, however, functional connectivity after tap onset was increased within a parietal-cerebellar loop, suggesting mismatch detection and update of the internal model. Data of the present study imply that anticipatory motor control is implemented in a network-like manner. Our data agree well with the hypothesis that functional connectivity in a cerebello-diencephalic-parietal loop might be crucial for anticipatory motor control, whereas parietal-cerebellar interaction might be critical for feedback processing.

The effect of rTMS over left and right dorsolateral premotor cortex on movement timing of either hand

It has been suggested that the left dorsolateral premotor cortex (dPMC) controls timing abilities of either hand. To further clarify its functional significance for movement timing, low-frequency repetitive transcranial magnetic stimulation (rTMS) was applied over the left and right dPMC, respectively, while subjects performed an auditorily paced finger-tapping task with each hand. rTMS over the left dPMC decreased tapping accuracy of both hands, whereas no behavioural effects occurred following right dPMC stimulation. To elucidate the time window in which left dPMC TMS disturbs synchronization abilities, pairs of TMS pulses were applied over the left dPMC and the left anterior parietal cortex serving as control condition. TMS pulses were applied randomly at 40 ms, 80 ms, 120 ms, 160 ms, 200 ms and 240 ms before pacer onset, as taps precede the pacing signal for about 20-60 ms. Again, the analysis revealed that TMS over the left dPMC disturbed synchronization abilities of either hand; however, this effect was shown at different times suggesting that the left dPMC affects the right M1 via at least one additional relay station. The present data support the hypothesis that the left dPMC is crucial for accurate timing of either hand. Additionally, they reveal a piece of evidence that the left dPMC affects the left hand not via a direct left dPMC-right M1 connection.

Inter- versus intramodal integration in sensorimotor synchronization: a combined behavioral and magnetoencephalographic study

Although the temporal occurrence of the pacing signal is predictable in sensorimotor synchronization tasks, normal subjects perform on-the-beat-tapping to an isochronous auditory metronome with an anticipatory error. This error originates from an intermodal task, that is, subjects have to bring information from the auditory and tactile modality to coincide. The aim of the present study was to illuminate whether the synchronization error is a finding specific to an intermodal timing task and whether the underlying cortical mechanisms are modality-specific or supramodal. We collected behavioral data and cortical evoked responses by magneto-encephalography (MEG) during performance of cross- and unimodal tapping-tasks. As expected, subjects showed negative asynchrony in performing an auditorily paced tapping task. However, no asynchrony emerged during tactile pacing, neither during pacing at the opposite finger nor at the toe. Analysis of cortical signals resulted in a three dipole model best explaining tap-contingent activity in all three conditions. The temporal behavior of the sources was similar between the conditions and, thus, modality independent. The localization of the two earlier activated sources was modality-independent as well whereas location of the third source varied with modality. In the auditory pacing condition it was localized in contralateral primary somatosensory cortex, during tactile pacing it was localized in contralateral posterior parietal cortex. In previous studies with auditory pacing the functional role of this third source was contradictory: A special temporal coupling pattern argued for involvement of the source in evaluating the temporal distance between tap and click whereas subsequent data gave no evidence for such an interpretation. Present data shed new light on this question by demonstrating differences between modalities in the localization of the third source with similar temporal behavior.

The role of the preSMA and the rostral cingulate zone in internally selected actions

In everyday life, one can differentiate between actions that are primarily internally guided and actions that are primarily guided by external events. FMRI studies investigating the neural correlates of internally guided actions usually report activation maxima in the rostral cingulate zone (RCZ) as well as the preSMA. However, the pertinent contrasts were often confounded by perceptual and motor differences between the different conditions. In the current study, we reinvestigated the neural correlates of internally vs. externally selected actions using a paradigm that avoids any such perceptual or motor confound. By doing so, we wanted to address the yet unsolved question which differential role the preSMA and RCZ play in internally guided actions. Subjects were required to make left or right key presses at the midpoint between isochronous pacing signals (a sequence of 'X's presented to the left or the right of the fixation point). In the internally selected condition, the location of the 'X' was determined by the location of the preceding key press that the subjects selected freely. In the externally selected condition, by contrast, the location of the 'X' prescribed the location of the subsequent key press response. We found that the RCZ was differentially activated by internally as compared to externally selected actions. In contrast to previous studies, the preSMA showed equal activity in both conditions and thus did not differentiate between the two modes of action selection. This suggests a primary role for the RCZ in internally selected actions.

Intercerebellar Coupling Contributes to Bimanual Coordination

Compared to unimanual task execution, simultaneous bimanual tapping tasks are associated with a significantly reduced intertap variability. It has been suggested that this bimanual advantage is based on the integration of timing signals which otherwise control each hand independently. Although its functional and anatomic foundations are poorly understood, functional coupling between cerebellar hemispheres might be behind this process. Because the execution of fast alternating fingertaps increases intertap variability, it is hypothesized that intercerebellar coupling is reduced in such tasks. To shed light on the functional significance of intercerebellar coupling, 14 right-handed subjects performed unimanual right, bimanual simultaneous, and bimanual alternating synchronization tasks with respect to a regular auditory pacing signal. In all conditions, within-hand intertap interval was 500 msec. Continuous neuromagnetic activity, using a 122-channel wholehead neuromagnetometer and surface electromyograms of the first dorsal interosseus muscle of both hands, were recorded. For data analysis, we used the analysis tool Dynamic Imaging of Coherent Sources, which provides a tomographic map of cerebromuscular and cerebrocerebral coherence. Analysis revealed a bilateral cerebello-thalamo-cortical network oscillating at alpha (8-12 Hz) and beta (13-24 Hz) frequencies associated with bimanual synchronization. In line with our hypothesis, coupling between cerebellar hemispheres was restricted to simultaneous task execution. This result implies that intercerebellar coupling is key for the execution of simultaneous bimanual movements. Although the criticality of a specific magneto-encephalography pattern for behavioral changes should be interpreted with caution, data suggest that intercerebellar coupling possibly represents the functional foundation of the bimanual advantage.

Motor timing and more – additional options using advanced registration and evaluation of tapping data

Motor coordination in multi-tasking situations is relevant to everyday life, since numerous daily activities require the performance of more than one task simultaneously. Investigations into this topic often use dual-task experiments like bimanual tapping, with different instructions for the right and left hands, such as to tap repetitively with the right index finger at a given frequency and to concurrently execute a single tap in response to a go signal with the left index finger. A basic experimental set-up for tapping consists of only a pace signal generator and ground contact sensors such as micro switches for observation of motor action. Evaluation of the binary on-off signals provided by these switches is quite simple, but the amount of information obtained is also limited. This paper presents a novel experimental design for tapping experiments with high-resolution recording of the complete time course of continuous finger movements. The evaluation procedures required for biomechanical and EMG data are described. The latter are based on sophisticated maximum-likelihood techniques, which is an example of progress in research using advanced biosignal processing.

The effect of sensory feedback on the timing of movements: Evidence from deafferented patients

The role of sensory feedback in the control of movements was investigated in two deafferented patients with complete loss of cutaneous touch and movement/position sense below the neck and two control groups of different ages. In a synchronized repetitive finger-tapping task in time with a regular auditory pacing signal, the deafferented participants showed a strong influence of extrinsic feedback. In contrast to controls who demonstrated a typical asynchrony between their taps and the pacing signal in all feedback conditions, the deafferented participants, with auditory feedback and visual monitoring, showed no asynchrony between finger taps and the pacing signal. These findings support the view that sensory information plays a crucial role in the anticipatory timing of movements.

Impaired rhythm generation in essential tremor

It has been suggested that the cerebellum plays a role in the event-based timing of synchronized repetitive movements. We hypothesized that regularity of rhythmic movements in essential tremor (ET) is impaired, since several lines of evidence suggest the involvement of the cerebellum in the pathomechanism of ET. To test this assumption, we examined the regularity and the maximum frequency of auditory paced repetitive movements at slow and fast stimulus rate in 34 ET patients. Variability of rhythmic finger tapping and alternating hand movements, defined by the standard deviation of movement offset before or after the pacing signal, was significantly higher compared to healthy controls. Timing of rhythmic movements of the two hands was disturbed to the same degree. Our results suggest a severe deficit of event-based rhythm generation on both sides in ET, supporting the presumed bilateral cerebellar dysfunction in this disorder.

Differences Between Intention-Based and Stimulus-Based Actions

Abstract: Actions carried out in response to exogenous stimuli and actions selected endogenously on the basis of intentions were compared in terms of their behavioral (movement timing) and electrophysiological (EEG) profiles. Participants performed a temporal bisection task that involved making left or right key presses at the midpoint between isochronous pacing signals (a sequence of centrally-presented letters). In separate conditions, the identity of each letter either (1) prescribed the location of the subsequent key press response (stimulus-based) or (2) was determined by the location of the preceding key press, in which case participants were instructed to generate a random sequence of letters (intention-based). The behavioral results indicated that stimulus-based movements occurred earlier in time than intention-based movements. The EEG results revealed that activity reflecting stimulus evaluation and response selection was most pronounced in the stimulus-based condition, whereas activity associated with the general readiness to act was strongest in the intention-based condition. Together, the behavioral and electrophysiological findings provide evidence for two modes of action planning, one mediated by stimulus-response bindings and the other by action-effect bindings. The comparison of our results to those of an earlier study ( Waszak et al., 2005 ) that employed spatially congruent visuo-motor mappings rather than symbolic visuo-motor mappings suggests that intention-based actions are controlled by similar neural pathways in both cases, but stimulus-based actions are not.

How the brain controls repetitive finger movements

Adequate interaction with our physical and social environment requires accurate timing abilities. Since planning and control of movements is closely related to sensorimotor synchronization, the investigation of synchronization abilities may allow insights into fundamental principles of motor behaviour. The finger-tapping task has frequently been used to study the synchronization of one’s own movements in relation to external events. Data from behavioural studies gave rise to the assumption that it is not the peripheral event (i.e., finger-tap or pacing signal) that is synchronized but its central representation. The neural foundations of sensorimotor synchronization have only recently been investigated and are still poorly understood. The present article reviews data from neurophysiological studies investigating sensorimotor synchronization to shed light on the neurophysiological processes associated with sensorimotor synchronization. This review focuses on studies investigating neuroelectric and neuromagnetic activity associated with simple repetitive synchronization tasks.

The oscillatory network of simple repetitive bimanual movements

Bimanual synchronization relies on the precisely coordinated interplay of both hands. It is assumed that during temporal bimanual coordination, timing signals controlling each hand might be integrated. Although a specific role of the cerebellum for this integration process has been suggested, its neural foundations are still poorly understood. Since dynamic interactions between spatially distributed neural activity are reflected in oscillatory neural coupling, the aim of the present study was to characterize the dynamic interplay between participating brain structures. More specifically, the study aimed at investigating whether any evidence for the integration of bilateral cerebellar hemispheres could be found. Seven right-handed subjects synchronized bimanual index finger-taps to a regular pacing signal. We recorded continuous neuromagnetic activity using a 122-channel whole-head neuromagnetometer and surface EMGs of the first dorsal interosseus (FDI) muscle of both hands. Coherence analysis revealed that an oscillatory network coupling at 8–12 Hz subserves task execution. The constituents are bilateral primary sensorimotor and premotor areas, posterior-parietal and primary auditory cortex, thalamus and cerebellum. Coupling occurred at different cortical and subcortical levels within and between both hemispheres. Coupling between primary sensorimotor and premotor areas was observed directly and indirectly via the thalamus. Coupling direction suggests that information was integrated within the left premotor cortex corroborating a specific role of the left premotor cortex for motor control in right-handers. Most importantly, our data indicate strong coupling between both cerebellar hemispheres substantiating the hypothesis that cerebellar signals might be integrated during task execution.