Tapping Movements Research Articles

Stepping to phase-perturbed metronome cues: multisensory advantage in movement synchrony but not correction.

Humans can synchronize movements with auditory beats or rhythms without apparent effort. This ability to entrain to the beat is considered automatic, such that any perturbations are corrected for, even if the perturbation was not consciously noted. Temporal correction of upper limb (e.g., finger tapping) and lower limb (e.g., stepping) movements to a phase perturbed auditory beat usually results in individuals being back in phase after just a few beats. When a metronome is presented in more than one sensory modality, a multisensory advantage is observed, with reduced temporal variability in finger tapping movements compared to unimodal conditions. Here, we investigate synchronization of lower limb movements (stepping in place) to auditory, visual and combined auditory-visual (AV) metronome cues. In addition, we compare movement corrections to phase advance and phase delay perturbations in the metronome for the three sensory modality conditions. We hypothesized that, as with upper limb movements, there would be a multisensory advantage, with stepping variability being lowest in the bimodal condition. As such, we further expected correction to the phase perturbation to be quickest in the bimodal condition. Our results revealed lower variability in the asynchronies between foot strikes and the metronome beats in the bimodal condition, compared to unimodal conditions. However, while participants corrected substantially quicker to perturbations in auditory compared to visual metronomes, there was no multisensory advantage in the phase correction task—correction under the bimodal condition was almost identical to the auditory-only (AO) condition. On the whole, we noted that corrections in the stepping task were smaller than those previously reported for finger tapping studies. We conclude that temporal corrections are not only affected by the reliability of the sensory information, but also the complexity of the movement itself.

Changes in cortical, cerebellar and basal ganglia representation after comprehensive long term unilateral hand motor training

We were interested in motor performance gain after unilateral hand motor training and associated changes of cerebral and cerebellar movement representation tested with functional magnetic resonance imaging (fMRI) before and after training. Therefore, we trained the left hand of strongly right-handed healthy participants with a comprehensive training (arm ability training, AAT) over two weeks. Motor performance was tested for the trained and non-trained hand before and after the training period. Functional imaging was performed for the trained and the non-trained hand separately and comprised force modulation with the fist, sequential finger movements and a fast writing task. After the training period the performance gain of tapping movements was comparable for both hand sides, whereas the motor performance for writing showed a higher training effect for the trained hand. fMRI showed a reduction of activation in supplementary motor, dorsolateral prefrontal cortex, parietal cortical areas and lateral cerebellar areas during sequential finger movements over time. During left hand writing lateral cerebellar hemisphere also showed reduced activation, while activation of the anterior cerebellar hemisphere was increased. An initially high anterior cerebellar activation magnitude was a predictive value for high training outcome of finger tapping and visual guided movements. During the force modulation task we found increased activation in the striate.Overall, a comprehensive long-term training of the less skillful hand in healthy participants resulted in relevant motor performance improvements, as well as an intermanual learning transfer differently pronounced for the type of movement tested. Whereas cortical motor area activation decreased over time, cerebellar anterior hemisphere and striatum activity seem to represent increasing resources after long-term motor training.

Upper limb function is normal in patients with restless legs syndrome (Willis-Ekbom Disease)

ObjectiveRestless legs syndrome, now called Willis-Ekbom Disease (RLS/WED), is a sensorimotor-related sleep disorder. Little is known of the effect of RLS/WED on motor function. The current study investigated upper limb function in RLS/WED patients. We hypothesised that RLS/WED patients exhibit subtle changes in tremor amplitude but normal dexterity and movement speed and rhythmicity compared to healthy controls. MethodsRLS/WED patients (n=17, 59±7years) with moderate disease and healthy controls (n=17, 58±6years) completed screening tests and five tasks including object manipulation, maximal pinch grip, flexion and extension of the index finger (tremor assessment), maximal finger tapping (movement speed and rhythmicity assessment), and the grooved pegboard test. Force, acceleration, and/or first dorsal interosseus EMG were recorded during four of the tasks. ResultsTask performance did not differ between groups. Learning was evident on tasks with repeated trials and the magnitude of learning did not differ between groups. ConclusionsHand function, tremor, and task learning were unaffected in RLS/WED patients. Patients manipulated objects in a normal manner and exhibited normal movement speed, rhythmicity, and tremor. SignificanceFurther research is needed to assess other types of movement in RLS/WED patients to gain insight into the motor circuitry affected and the underlying pathophysiology.

Motor coordination uses external spatial coordinates independent of developmental vision

The constraints that guide bimanual movement coordination are informative about the processing principles underlying movement planning in humans. For example, symmetry relative to the body midline benefits finger and hand movements independent of hand posture. This symmetry constraint has been interpreted to indicate that movement coordination is guided by a perceptual code. Although it has been assumed implicitly that the perceptual system at the heart of this constraint is vision, this relationship has not been tested. Here, congenitally blind and sighted participants made symmetrical and non-symmetrical (that is, parallel) bimanual tapping and finger oscillation movements. For both groups, symmetrical movements were executed more correctly than parallel movements, independent of anatomical constraints like finger homology and hand posture. For the blind, the reliance on external spatial factors in movement coordination stands in stark contrast to their use of an anatomical reference frame in perceptual processing. Thus, the externally coded symmetry constraint evident in bimanual coordination can develop in the absence of the visual system, suggesting that the visual system is not critical for the establishment of an external-spatial reference frame in movement coordination.

Decoding repetitive finger movements with brain activity acquired via non-invasive electroencephalography

We investigated how well repetitive finger tapping movements can be decoded from scalp electroencephalography (EEG) signals. A linear decoder with memory was used to infer continuous index finger angular velocities from the low-pass filtered fluctuations of the amplitude of a plurality of EEG signals distributed across the scalp. To evaluate the accuracy of the decoder, the Pearson's correlation coefficient (r) between the observed and predicted trajectories was calculated in a 10-fold cross-validation scheme. We also assessed attempts to decode finger kinematics from EEG data that was cleaned with independent component analysis (ICA), EEG data from peripheral sensors, and EEG data from rest periods. A genetic algorithm (GA) was used to select combinations of EEG channels that maximized decoding accuracies. Our results (lower quartile r = 0.18, median r = 0.36, upper quartile r = 0.50) show that delta-band EEG signals contain useful information that can be used to infer finger kinematics. Further, the highest decoding accuracies were characterized by highly correlated delta band EEG activity mostly localized to the contralateral central areas of the scalp. Spectral analysis of EEG also showed bilateral alpha band (8–13 Hz) event related desynchronizations (ERDs) and contralateral beta band (20–30 Hz) event related synchronizations (ERSs) localized over central scalp areas. Overall, this study demonstrates the feasibility of decoding finger kinematics from scalp EEG signals.

Monkeys time their pauses of movement and not their movement-kinematics during a synchronization-continuation rhythmic task

A critical question in tapping behavior is to understand whether the temporal control is exerted on the duration and trajectory of the downward-upward hand movement or on the pause between hand movements. In the present study, we determined the duration of both the movement execution and pauses of monkeys performing a synchronization-continuation task (SCT), using the speed profile of their tapping behavior. We found a linear increase in the variance of pause-duration as a function of interval, while the variance of the motor implementation was relatively constant across intervals. In fact, 96% of the variability of the duration of a complete tapping cycle (pause + movement) was due to the variability of the pause duration. In addition, we performed a Bayesian model selection to determine the effect of interval duration (450-1,000 ms), serial-order (1-6 produced intervals), task phase (sensory cued or internally driven), and marker modality (auditory or visual) on the duration of the movement-pause and tapping movement. The results showed that the most important parameter used to successfully perform the SCT was the control of the pause duration. We also found that the kinematics of the tapping movements was concordant with a stereotyped ballistic control of the hand pressing the push-button. The present findings support the idea that monkeys used an explicit timing strategy to perform the SCT, where a dedicated timing mechanism controlled the duration of the pauses of movement, while also triggered the execution of fixed movements across each interval of the rhythmic sequence.

Spontaneous sensorimotor coupling with multipart music.

Music often evokes spontaneous movements in listeners that are synchronized with the music, a phenomenon that has been characterized as being in "the groove." However, the musical factors that contribute to listeners' initiation of stimulus-coupled action remain unclear. Evidence suggests that newly appearing objects in auditory scenes orient listeners' attention, and that in multipart music, newly appearing instrument or voice parts can engage listeners' attention and elicit arousal. We posit that attentional engagement with music can influence listeners' spontaneous stimulus-coupled movement. Here, 2 experiments-involving participants with and without musical training-tested the effect of staggering instrument entrances across time and varying the number of concurrent instrument parts within novel multipart music on listeners' engagement with the music, as assessed by spontaneous sensorimotor behavior and self-reports. Experiment 1 assessed listeners' moment-to-moment ratings of perceived groove, and Experiment 2 examined their spontaneous tapping and head movements. We found that, for both musically trained and untrained participants, music with more instruments led to higher ratings of perceived groove, and that music with staggered instrument entrances elicited both increased sensorimotor coupling and increased reports of perceived groove. Although untrained participants were more likely to rate music as higher in groove, trained participants showed greater propensity for tapping along, and they did so more accurately. The quality of synchronization of head movements with the music, however, did not differ as a function of training. Our results shed new light on the relationship between complex musical scenes, attention, and spontaneous sensorimotor behavior.

Neurophysiology of timing in the hundreds of milliseconds: multiple layers of neuronal clocks in the medial premotor areas.

The precise quantification of time in the subsecond scale is critical for many complex behaviors including music and dance appreciation/execution, speech comprehension/articulation, and the performance of many sports. Nevertheless, its neural underpinnings are largely unknown. Recent neurophysiological experiments from our laboratory have shown that the cell activity in the medial premotor areas (MPC) of macaques can represent different aspects of temporal processing during a synchronization-continuation tapping task (SCT). In this task the rhythmic behavior of monkeys was synchronized to a metronome of isochronous stimuli in the hundreds of milliseconds range (synchronization phase), followed by a period where animals internally temporalized their movements (continuation phase). Overall, we found that the time-keeping mechanism in MPC is governed by different layers of neural clocks. Close to the temporal control of movements are two separate populations of ramping cells that code for elapsed or remaining time for a tapping movement during the SCT. Thus, the sensorimotor loops engaged during the task may depend on the cyclic interplay between two neuronal chronometers that quantify in their instantaneous discharge rate the time passed and the remaining time for an action. In addition, we found MPC neurons that are tuned to the duration of produced intervals during the rhythmic task, showing an orderly variation in the average discharge rate as a function of duration. All the tested durations in the subsecond scale were represented in the preferred intervals of the cell population. Most of the interval-tuned cells were also tuned to the ordinal structure of the six intervals produced sequentially in the SCT. Hence, this next level of temporal processing may work as the notes of a musical score, providing information to the timing network about what duration and ordinal element of the sequence are being executed. Finally, we describe how the timing circuit can use a dynamic neural representation of the passage of time and the context in which the intervals are executed by integrating the time-varying activity of populations of cells. These neural population clocks can be defined as distinct trajectories in the multidimensional cell response-space. We provide a hypothesis of how these different levels of neural clocks can interact to constitute a coherent timing machine that controls the rhythmic behavior during the SCT.

Characteristics of 3-min self-paced tapping movement of the index finger and ankle-toe in the elderly

Characteristics of 3-min self-paced tapping movement of the index finger and ankle-toe in the elderly

Gait and upper limb variability in Parkinson’s disease patients with and without freezing of gait

Patients with Parkinson's disease (PD) and freezing of gait (FOG) (freezers) demonstrate high gait variability. The objective of this study was to determine whether freezers display a higher variability of upper limb movements and elucidate if these changes correlate with gait. We were the first group to compare directly objectively measured gait and upper limb movement variability of freezers between freezing episodes. Patients with objectively verified FOG (n=11) and PD patients without FOG (non-freezers) (n=11) in a non-randomized medication condition (OFF/ON) were analyzed. Uncued antiphasic finger tapping and forearm diadochokinetic movements were analyzed via three-dimensional ultrasound kinematic measurements. Gait variability of straight gait was assessed using ground reaction forces. Freezers had shorter stride length (p=0.004) and higher stride length variability (p=0.005) in the medication OFF condition. Movement variability was not different during finger tapping or diadochokinesia between the groups. There was a trend towards more freezing of the upper limb during finger tapping for the freezers (p=0.07). Variability in stride length generation and stride timing was not associated with variability of upper limb movement in freezers. Our findings demonstrate that: (1) freezers have a higher spatial gait variability between freezing episodes; (2) freezing-like episodes of the upper limb occur in PD patients, and tend to be more pronounced among freezers than non-freezers for finger tapping; (3) spatial and temporal upper extremity variability is equally affected in freezers and non-freezers in an uncued task. Upper limb freezing is not correlated to lower limb freezing, implicating a different pathophysiology.

Age-related changes in the bimanual advantage and in brain oscillatory activity during tapping movements suggest a decline in processing sensory reafference

Deficits in the processing of sensory reafferences have been suggested as accounting for age-related decline in motor coordination. Whether sensory reafferences are accurately processed can be assessed based on the bimanual advantage in tapping: because of tapping with an additional hand increases kinesthetic reafferences, bimanual tapping is characterized by a reduced inter-tap interval variability than unimanual tapping. A suppression of the bimanual advantage would thus indicate a deficit in sensory reafference. We tested whether elderly indeed show a reduced bimanual advantage by measuring unimanual (UM) and bimanual (BM) self-paced tapping performance in groups of young (n = 29) and old (n = 27) healthy adults. Electroencephalogram was recorded to assess the underlying patterns of oscillatory activity, a neurophysiological mechanism advanced to support the integration of sensory reafferences. Behaviorally, there was a significant interaction between the factors tapping condition and age group at the level of the inter-tap interval variability, driven by a lower variability in BM than UM tapping in the young, but not in the elderly group. This result indicates that in self-paced tapping, the bimanual advantage is absent in elderly. Electrophysiological results revealed an interaction between tapping condition and age group on low beta band (14-20 Hz) activity. Beta activity varied depending on the tapping condition in the elderly but not in the young group. Source estimations localized this effect within left superior parietal and left occipital areas. We interpret our results in terms of engagement of different mechanisms in the elderly depending on the tapping mode: a 'kinesthetic' mechanism for UM and a 'visual imagery' mechanism for BM tapping movement.

Performance of a motor task learned on levodopa deteriorates when subsequently practiced off

Studies in animals and in people with Parkinson's disease (PD) demonstrate complex effects of dopamine on learning motor tasks; its effect on retention of motor learning has received little attention. Recent animal studies demonstrate that practicing a task in the off state, when initially learned in the on state, leads to progressive deterioration in performance. We measured the acquisition and retention of 3 different motor tasks in the presence and absence of levodopa. Twenty individuals with Hoehn and Yahr Stage 1.5 to 3 PD practiced the tasks daily for two 4-day weeks, one half practicing on L-dopa the first week and off the second week. The other half practiced off l-dopa both weeks. The tasks were (1) alternate tapping of 2 keys, (2) moving the body toward 2 targets on a posturography device, and (3) mirror drawing of a star. For the tapping and body movement tests, those who practiced on the first week had a progressive decline in performance with practice during week 2, while subjects off during week 1 maintained or improved. In contrast, for the mirror task, subjects on L-dopa initially had much more difficulty completing the task compared to subjects who practiced off. Both groups improved with practice the first week and had flat performance the second week. These data suggest that performance of speed-accuracy tasks learned in the on state may progressively worsen if subsequently practiced in the off state. In addition, performance, but not learning, of some tasks may be impeded by L-dopa.

Computerized Measures of Finger Tapping: Effects of Hand Dominance, Age, and Sex

Computerized measures of digit tapping rate were obtained over 3 successive, 10-sec. periods in the right and left index fingers, from a community sample of 1,519 participants (ages 18 to 65 years; 607 men, 912 women). Differences between the dominant and non-dominant hands were found for tapping rate, movement initiation, and button down times, and the decline in tapping rate over the successive, 10-sec. periods. Declines were found in tapping rate in older participants in association with increased intertap variability. Men had higher tapping rates than women in all age ranges. The computerized finger tapping test is an efficient and precise measure of tapping speed and kinetics of potential utility in research and clinical studies of motor performance.

Power spectral density analysis of physiological, rest and action tremor in Parkinson’s disease patients treated with deep brain stimulation

BackgroundObservation of the signals recorded from the extremities of Parkinson’s disease patients showing rest and/or action tremor reveal a distinct high power resonance peak in the frequency band corresponding to tremor. The aim of the study was to investigate, using quantitative measures, how clinically effective and less effective deep brain stimulation protocols redistribute movement power over the frequency bands associated with movement, pathological and physiological tremor, and whether normal physiological tremor may reappear during those periods that tremor is absent.MethodsThe power spectral density patterns of rest and action tremor were studied in 7 Parkinson’s disease patients treated with (bilateral) deep brain stimulation of the subthalamic nucleus. Two tests were carried out: 1) the patient was sitting at rest; 2) the patient performed a hand or foot tapping movement. Each test was repeated four times for each extremity with different stimulation settings applied during each repetition. Tremor intermittency was taken into account by classifying each 3-second window of the recorded angular velocity signals as a tremor or non-tremor window.ResultsThe distribution of power over the low frequency band (<3.5 Hz – voluntary movement), tremor band (3.5-7.5 Hz) and high frequency band (>7.5 Hz – normal physiological tremor) revealed that rest and action tremor show a similar power-frequency shift related to tremor absence and presence: when tremor is present most power is contained in the tremor frequency band; when tremor is absent lower frequencies dominate. Even under resting conditions a relatively large low frequency component became prominent, which seemed to compensate for tremor. Tremor absence did not result in the reappearance of normal physiological tremor.ConclusionParkinson’s disease patients continuously balance between tremor and tremor suppression or compensation expressed by power shifts between the low frequency band and the tremor frequency band during rest and voluntary motor actions. This balance shows that the pathological tremor is either on or off, with the latter state not resembling that of a healthy subject. Deep brain stimulation can reverse the balance thereby either switching tremor on or off.

因子分析によるパーキンソン病患者の指タップ運動機能評価と分類

因子分析によるパーキンソン病患者の指タップ運動機能評価と分類

Impact of hand orientation on bimanual finger coordination in an eight-finger tapping task

In the present experiment we examined whether a symmetry tendency in bimanual finger coordination is observable in an experimental setting resembling a serial learning task and whether this tendency is defined in hand-based coordinates. Participants performed an eight-finger bimanual coordination task, in which they responded to sequences of visual stimuli by sequences of tapping movements. Visual stimuli triggered flexion of fingers, which were parallel or mirror symmetrical in respect to the body midline. Additionally, the orientation of the right hand relative to the left hand was varied. When both hands had the same orientation, the mirror symmetrical mode was more stable than the parallel mode. When both hands had different orientations, in contrast, the parallel mode was more stable. This result suggests that the tendency towards mirror symmetry was defined in hand-based coordinates. This outcome is relevant for the research of skill learning regarding the issue of whether acquired sequence knowledge is tied to specific effectors.

Investigating the neural correlates of goal-oriented upper extremity movements

To understand neural correlates of upper extremity task performance (functional vs. non-functional) and to understand their influence on neuromotor control strategies. Cross-sectional descriptive study, with repeated measures. Medical center 1.5T MRI clinical imaging facility. Neurologically intact individuals, (M=14 F=5 mean age=22.94 ± 3.1 years) all right hand dominant as determined by the Edinburgh handedness survey. Subjects performed upper extremity motor tasks of reaching and grasping in a block paradigm. Whole brain fMRI data was acquired using a 1.5T MRI scanner. Differences in fMRI area of activation and maximum activation intensity for the whole brain were evaluated among the different upper extremity motor tasks. Our results indicate (a) Activations in brain regions are task specific. (b) ANOVA results indicate functional goal oriented movements of reaching and grasping produce higher activation intensity (p < 0.0001) in more regions of the cortex (Somatosensory motor area, primary motor cortex, and parietal region) and cerebellum (p < 0.001) as compared to nonfunctional rhythmic movements of reaching only and grasping only. (c) There is some overlap in cerebellar activations, however areas of activation in the medial cerebellum were observed for reaching-and-grasping, while the grasping-only task produced activation more laterally in the cerebellum. Our findings suggest that (a) neuromotor strategy for functional goal-oriented movements is different from rhythmic movements such as finger tapping or non-functional movements, (b) This difference can be quantified and mapped using fMRI. (c) There are some overlap with activation of movement execution however the cognitive component that mediates the specific movement is not just the linear combination of simple movements rather it is task and context specific. (d) The results support the concept of using goal-oriented tasks in the applications of rehabilitation and therapy for restoration of function.

Trial time warping to discriminate stimulus-related from movement-related neural activity

In tasks where different sensory, cognitive, and motor events are mixed in a sequence it is difficult to determine whether neural activity is related to any behavioral parameter. Here, we consider the case in which two alternative trial-alignment schemes correspond to two different neural representations, one stimulus-related and the other movement-related, using both simulations of neural activity and real recordings in the medial premotor areas during a multiple-interval tapping task called synchronization-continuation task (SCT). To discover whether neural responses are better aligned to sensory or motor events we introduce a family of trial-alignment time-warping functions indexed by a single parameter such that when the parameter takes the value 0 the trials are aligned to the stimulus and when the parameter takes the value 1 they are aligned to the movement. We then characterize neurons by the best-fitting alignment scheme (in the sense of maximum likelihood) under the assumption that the correct alignment would produce homogeneous trials without excess trial-to-trial variation. We use Bayes factors to determine the evidence in favor of sensory or motor neural alignments. The simulations revealed that the variability in neural responses and sequential motor outputs are key parameters to obtain appropriate warping results. In addition, the analysis on the activity of 500 neurons in the medial premotor areas of monkeys executing the SCT showed that most of the neural responses (54.2%) were aligned to the tapping movements instead of the stimuli used to drive the temporal behavior.

Can’t you find me? Female sexual response in an Argentinean tarantula (Araneae, Theraphosidae)

We described and analyzed the female sexual response in the tarantula Grammostola vachoni Schiapelli and Gerschman 1961 under three series of 10 experiments each with different situations for the male-female encounters: male free in terrarium but with no access to female; male confined into a glass cup at 30 cm of female burrow and; male confined into a glass cup over a heavy stone closing the female burrow. We observed leg palpal tapping and body movements of female in response to male courtship. Leg and palpal tapping could indicate a female receptive condition and her attractiveness. Also, this behavior may serve to orient male towards her location. These females responded with leg and palpal tapping only to males which present long courtships together with active searching (walking) for female location. The female body movements, originated by legs III, are interpreted here as a rejection considering that male stopped courting and tried to escape.

On the sensory cues that permit control of movements accompanying periodic stimuli (1958).

Translated from the French1,2 by Bruno H. ReppPeriodic stimulation induces voluntary and involuntary periodic movements. We have in mind here the soldier who adjusts his step to [the beat of]3 a military march or the music lover who accom- panies, with [taps of] the foot or the hand, the musical tunes that the radio or a record player delivers to him, often without realizing it. We have previously studied these induced movements in rela- tion to the nature of the music and to the posture and attitude of the subject (Fraisse, Oleron, & Paillard, 1953; Paillard, Oleron, & Fraisse, 1953). However, several observations made in the course of this research have led us to address new issues. The induced movement is, in effect, synchronous with the stimulus; it does not follow the stimulus but accompanies it, and its [motor] command must therefore be anticipated. This necessity means that motor induction cannot occur unless the stimulation obeys a law of periodicity that somehow permits [the subject] to predict the moment at which the [next] stimulus will occur.4 However, this anticipated [motor] command cannot lead to adequate synchroni- zation unless some feedback5 process permits the subject to con- trol-without awareness, incidentally-the simultaneity of the movement and the stimulus. In the course of our experiments, we were rightly struck by the fact that motor induction occurs pref- erentially in limbs that have support, that is to say, in limbs whose induced movement could easily be translated into a tap of the foot or the hand on a surface. The proof of this is that when the arm hangs alongside the body, motor induction is uncommon; but when induction does occur, the subject searches in some way for a place where the hand can tap, for example, his thigh or the leg of the chair.The problem was then to ascertain the nature of the stimulus or stimuli coming from the movement, whose simultaneity with the sound stimuli could control the [time of] occurrence of the induced movements. Analysis [of the problem] allowed us to predict that three kinds of stimuli could emanate from the movement: Kines- thetic cues obviously, but also tactile cues (from touching a sur- face) or auditory cues (sound of the tap on a surface). Kinesthetic cues are necessarily always present, [whereas] tactile and auditory cues can be either present or absent. An observation that we have made on many occasions is that tactile or auditory cues are, if not necessary, at least useful. Our aim thus has been to investigate the respective roles of the different kinds of cues [obtained] from movement.Our method consisted of comparing spatially free induced movements with induced tapping movements, and movements that produce a sound, with or without a tap, with movements that do not produce any sound. We have, moreover, tried to reveal sys- tematically the relative role of auditory cues by using an apparatus for creating delays that enabled us to dissociate the moment at which the sound of the response was triggered from the moment at which it was perceived.MethodThe principle [of the method] was simple.6 The subject heard a sound that was repeated indefinitely with an [interonset] interval of 580 ms.7 These sounds were recorded by a polygraph. The task was to accompany [each] stimulus with a downward8 movement of the wrist.The subject was seated comfortably, with the forearm resting on a support and the wrist free. He held in his hand a baton on top of which was mounted a piece of Bristol board in the shape of a flag (see Figure 1). Moreover, at the far end of the baton, there was a Plexiglas eyelet through which a very light metal rod slid in and out, which controlled the rotation of a potentiometer. This poten- tiometer was connected to the pen of a recorder, which thus permitted us to record the form of the movement graphically and yielded a very precise measure of the moments at which the movement stopped in the downward and upward directions. …