Hand coordination in bimanual circle drawing.

Two right-handed and 2 left-handed participants drew circles in the horizontal plane with both hands simultaneously in either a symmetrical or an asymmetrical mode, at their preferred rate or as fast as possible. During symmetrical movements, the hands showed frequency and phase synchronization at both rates. During fast asymmetrical movements, the hands showed increased phase difference and phase variability, as well as transitions to symmetrical movements, and cases of frequency decoupling. Large distortions of the hand trajectory were also observed under fast asymmetrical movements. Trajectory distortions and movement direction reversals were confined to the nondominant hand. Under the assumption that circular trajectories are generated by properly timed orthogonal oscillations along the y-axis and the x-axis, these findings are accounted for by the characteristics of coupling between homologous functional oscillators of the 2 body sides. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distinguishing between the effects of frequency and amplitude on interlimb coupling in tapping a 2:3 polyrhythm

Rhythmic interlimb coordination is characterized by attraction to stable phase and frequency relations. Sudden, unintended transitions between such coordination patterns have been observed in iso- and multifrequency tasks when movement frequency was gradually increased. These transitions have been accounted for by modeling the two limbs as nonlinearly coupled oscillators. The prevailing form of the coupling function is based on time derivatives, but an alternative formulation can be derived by incorporating time delays. These time delays may be related to the neurophysiological delays associated with the use of kinesthetic afferences. The two ways of deriving coupling functions for interlimb coordination allow for different predictions with respect to the effects of movement frequency and amplitude on the strength of interaction between the limbs. In the current experiment, the effects of amplitude and frequency were dissociated experimentally, so as to arrive at an empirically motivated choice between the two ways of formalizing interlimb coupling. Subjects tapped the polyrhythm 2:3 at five different frequencies under three amplitude conditions. Whereas no effects of amplitude were observed, the strength of interaction between the hands decreased with increasing movement frequency. These results support the time-delay version of the model, in which differential (loss of) stability of coordination modes results from differential dependence on movement amplitude, but overall coupling strength is related reciprocally to movement frequency squared. This version of the model was related tentatively to three proposed aspects of interlimb coordination: (1) neurophysiological delays associated with the use of kinesthetic afferences; (2) rate-dependent decrease in pattern stability; and (3) differential entrainment influences of kinesthetic signals.     

Graft decentration in penetrating keratoplasty: nonmechanical trephination with the excimer laser (193 nm) versus the motor trephine

Seven right-handed participants performed bimanual circling movements in either a symmetrical or an asymmetrical coordination mode. Movements were paced with an auditory metronome at predetermined frequencies corresponding to transition frequency, where asymmetrical patterns became unstable, or at two-thirds transition frequency where both symmetrical and asymmetrical patterns were stable. The pacing tones were presented in either a high (1000 Hz) or low (500 Hz) pitch, and the percentage of high-pitched tones during a 20 s trial varied between 0% and 70%. Participants were instructed to count the number of high-pitched pacing tones that occurred during a trial of bimanual circling. Overall, the symmetrical pattern was more stable than the asymmetrical pattern at both frequencies. Errors on the tone-counting task were significantly higher during asymmetrical circling than symmetrical circling but only at the transition movement frequency. The results suggest that cognitive processes play a role in maintaining coordination patterns within regions of instability.     

Development of bilateral motor control in children with developmental coordination disorders

This research examined behavioral (i.e. movement time) and neuromuscular (EMG) characteristics of unilateral and bilateral aiming movements of children with normal motor development and children with developmental coordination disorders (DCD). Two age groups of children were studied: 6 to 7, and 9 to 10 year olds. Bilateral aiming movements involved moving the two hands to targets of either (1) the same amplitude--symmetrical bilateral movements, or (2) different amplitudes--asymmetrical bilateral movements. Unilateral aiming movements involved moving one hand to either near or far targets associated with that hand. In general, unilateral and bilateral movement times were slower in younger than older children, and in children with DCD than children with normal motor development. Our neuromuscular data suggest that the faster movement times that typically accompany increasing age in children may be the result of a change in the capacity to initiate antagonist muscle contractions. The prolonged burst of agonist activity and delayed onset of antagonist activity observed in children with DCD may contribute to their inability to produce fast, accurate unilateral movements. On both symmetrical and asymmetrical bilateral aiming movements, children with DCD had more performance errors and greater temporal inconsistencies between neuromuscular (EMG) parameters and behavioral (movement time) parameters than children with normal motor development. These new neuromuscular data suggest that there are important differences in the way the motor control systems of children with and without DCD organize bilateral aiming responses.     

Anomalous bimanual coordination among dyslexic boys.

Dyslexia has been associated with left-hemisphere dysfunctions; however, recent studies also suggest interhemispheric difficulties. To test this, we assessed bimanual coordination in dyslexic and nondisabled boys using an Etch-a-Sketch-like task. Group performance was equivalent for parallel hand movements (both clockwise). However, the dyslexics showed significant impairments on mirror movements, particularly in their left hands, and often unknowingly reverted to parallel movements when visual feedback was removed. Although these difficulties generally suggest impaired interhemispheric coordination, specific mirror movement deficits have never before been observed in any population. We propose that deficient interhemispheric collaboration combined with anomalous ipsilateral manual control may account for the dyslexics' performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of intra- and interpersonal interlimb coordination: coordination breakdowns and coupling strength

Intra- and interpersonal interlimb coordination of pendulums swung from the wrist was investigated. For both kinds of coordination, the steady state and breakdown of bimanual rhythmic coordination as indexed by the time series of the relative phase angle phi were studied under the manipulation of coordination mode, frequency of oscillation, and the difference in the eigenfrequencies (preferred tempos) of the individual oscillating limbs. The properties observed for both intra- and interpersonal coordination were those predicted by a dynamical model of rhythmic coordination that considers the coordinated limbs coupled to be nonlinear oscillators. Using a regression method, the coupling strengths of the coupled system were recovered. As predicted by the dynamical model, the strength of the dynamic was generally greater for the in-phase than the anti-phase mode and decreased with increasing frequency. Further, the strength of the interpersonal interlimb coupling was weaker than that of intrapersonal interlimb coupling.     

Spinal cord coordination of hindlimb movements in the turtle: intralimb temporal relationships during scratching and swimming

Hindlimb interlimb coordination was examined in turtles during symmetrical "same-form" behaviors in which both hindlimbs utilized the same movement strategy ("form") and during asymmetric "mixed-form" behaviors in which the form exhibited by one hindlimb differed from that of its contralateral partner. In spinal turtles, three forms of scratching were examined: rostral, pocket, and caudal. Bilateral symmetrical same-form scratching was studied for each of the forms. Asymmetric mixed-form scratching (rostral scratching of a hindlimb and pocket scratching of the other hindlimb) was also examined. In intact turtles, two forms of swimming were examined: forward swimming and back-paddling. The symmetrical behavior of bilateral forward same-form swimming and the asymmetric behavior of turning mixed-form swimming (forward swimming of 1 hindlimb and back-paddling of the other hindlimb) were studied. For all behaviors examined, most episodes displayed absolute or 1:1 coordination; in this type of coordination, during each movement cycle that began and ended with the onset of ipsilateral hip flexion, there was a single onset of contralateral hip flexion. For most of these episodes there was out-of-phase coordination between hip movements; the onset of contralateral hip flexion occurred near the onset of ipsilateral hip extension midway through the ipsilateral movement cycle. Bilateral caudal/caudal same-form scratching displayed out-of-phase 1:1 coordination during some episodes and in-phase 1:1 coordination during other episodes. During in-phase coordination, the onset of contralateral hip flexion occurred near the onset of ipsilateral hip flexion close to the start of the ipsilateral movement cycle. In a few cases of bilateral same-form scratching there were episodes of relative or 2:1 coordination; in this type of coordination, during each movement cycle of the slowly moving limb that began and ended with ipsilateral hip flexion, there were two distinct occurrences of the onset of contralateral hip flexion. The observation that out-of-phase movements of the hip occurred during symmetrical as well as asymmetric behaviors is consistent with the hypothesis that timing signals related to hip movement play a major role in interlimb phase control. The neural mechanisms responsible for interlimb phase control are not well understood in vertebrates. The present demonstration of bilateral scratching in spinal turtles suggests that this preparation may be suitable for additional experiments to examine mechanisms of vertebrate interlimb phase control.     

Acquiring bimanual skills: Contrasting forms of information feedback for interlimb decoupling.

Addressed the learner's capability to perform different upper-limb actions simultaneously with the help of various sources of information feedback. An elbow flexion movement was made in the left limb together with a flexion-extension-flexion movement in the right limb. Interlimb interactions were assessed at the structural as well as the metrical level of movement specification during acquisition and retention. Despite a strong initial tendency for the limbs to be synchronized, findings revealed that Ss became gradually more successful in interlimb decoupling as a result of practice with augmented feedback. However, detailed knowledge of movement kinematics was no more effective than global outcome information for interlimb decoupling, indicating that knowledge of results may have more potential for acquiring multiple degree-of-freedom tasks than previously believed. Finally, the data support the general notion that learning new coordination tasks involves the suppression of preexisting preferred coordination tendencies, which is often a prerequisite for building new coordination modes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Handedness and the asymmetric dynamics of bimanual rhythmic coordination.

Human handedness was investigated in a 1:1 interlimb rhythmic coordination in which consistent and inconsistent left-handed and right-handed individuals oscillated hand-held pendulums. Mean phase difference (φstable) and its standard deviation (SDφ) were evaluated as functions of mode of coordination (in-phase vs anti-phase) and the symmetry conditions imposed by controlling the natural frequencies of the left and right pendulums. The dependencies of φstable and SDφ on coordination mode and imposed symmetry were found to be systematically affected by handedness. The data were consistent with an elaboration of the established order parameter dynamics of interlimb rhythmic coordination. The elaboration includes additional 27π periodic terms that break the symmetry of those dynamics when the natural frequencies of the component rhythmic units are identical. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Direction of motion relationships between controls and displays moving in different planes.

"… to investigate the direction of motion relationships for seven combinations of display pointer moving at right angles to plane of rotation of control knob, a total of 718 Ss were tested by sequential methods on an apparatus producing a single direction of movement of a pointer, moving along a linear scale, for either clockwise or anticlockwise rotation of the control… where the right hand was used, there was a significant tendency to turn the knob clockwise to produce movement away from the knob [but]… there was also a significant tendency for movement towards the knob to be mediated by clockwise turning… [there were, however] significantly more anticlockwise responses for movement towards the control… . Left-handed combinations gave rise to no significant tendencies; but left-handed Ss gave significantly more anticlockwise responses than right-handers, even when the right hand was used. On the whole it is not advisable to employ any of the combinations explored in this investigation, unless movement is to be restricted to adjustments in one direction only relative to the control." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rate and timing precision of motor coordination in developmental dyslexia.

Temporal characteristics of interlimb coordination were examined in adolescents and young adults with developmental dyslexia, matched normal control subjects, and matched learning disabled adolescent students without reading difficulties. Subjects were asked to tap in time to an entraining metronome at each of 3 prescribed rates by moving the index fingers of both hands in unison, in rhythmical alternation, or in more complex bimanual patterns. Dyslexic subjects showed significant deficits of timing precision on bimanual tasks that required the integration of asynchronous responses, but not when they moved the fingers in unison. Findings are discussed in terms of both the hypothesis that impaired temporal resolution in dyslexia reflects an underlying deficit of left-hemisphere function and an alternative hypothesis that functional deficits in developmental dyslexia are associated with impaired interhemispheric communication. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coupling dynamics in interlimb coordination.

In 1:1 frequency locking, the interlimb phase difference Φ is an order parameter quantifying the spatial-temporal organization of 2 rhythmic subsystems. Dynamical modeling and experimental analyses indicate that an intentional parameter Φψ (intended coordination mode, Φ?=?0° or Φ?=?180°) and 2 control parameters ωc (coupled frequency) and Δω (difference between uncoupled eigenfrequencies) affect Φ. An experiment was conducted on 1:1 frequency locking in which Φψ, ωc, and Δω were manipulated using a paradigm in which a person swings hand-held pendulums. As Δω deviated from 0, the observed Φ deviated from the Φψ, indicating a displacement in the Φ attractor point. The displacements were exaggerated by increasing ωc. The displacements were coordinated with a decrease in the stability of Φ and with higher harmonics in power spectrum of Φ. Implications of the results for modeling interlimb coordination are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Proprioceptive consequences of tendon vibration during movement

1. Previous studies have used tendon vibration to investigate kinesthetic illusions in the isometric limb and end point control in the moving limb. These previous studies have shown that vibration distorts the perceptions of static joint angle and movement and causes systematic errors in the end point of movement. In this paper we describe the effects of tendon vibration during movement while human subjects performed a proprioceptively coordinated motor task. In an earlier study we showed that the CNS coordinates this motor task-a movement sequence-with proprioceptive information related to the dynamic position and velocity of the limb. 2. When performing this movement sequence, each subject sat at a table and opened the right hand as the right elbow was passively rotated in the extension direction through a prescribed target angle. Vision of the arm was prevented, and the movement velocity was changed randomly from trial to trial, leaving proprioception as the only useful source of kinematic information with which to perform the task. 3. In randomly occurring trials, vibration was applied to the tendon of the biceps brachii, a muscle that lengthens during elbow extension. In some experiments the timing of tendon vibration was varied with respect to the onset of elbow rotation, and in other experiments the frequency of vibration was varied. In each experiment we compared the accuracy of the subject's response (i.e., the elbow angle at which the subject opened the hand) in trials with tendon vibration with the accuracy in trials without tendon vibration. 4. The effect of tendon vibration depended on the frequency of vibration. When the biceps tendon was vibrated at 20 Hz, subjects opened the hand after the elbow passed through the target angle ("overshooting"). Overshooting is consistent with an underestimate of the actual displacement or velocity of the elbow. Vibration at 30 Hz had little or no effect on the elbow angle at hand opening. Vibration at 40 Hz caused subjects to open the hand before the elbow reached the target angle ("undershooting"). Undershooting is consistent with an overestimate of the actual displacement or velocity of the elbow. The size of the error depended on the velocity of the passively imposed elbow rotation. 5. The effect of tendon vibration also depended on the timing of vibration. If 40-Hz vibration began at the onset of movement, the subject undershot the target. If 40-Hz vibration started 5 s before movement onset and continued throughout the movement, the undershoot error increased in magnitude. However, if 40-Hz vibration started 5 s before movement onset and then stopped at movement onset, the subject overshot the target. When vibration was shut off during movement, a transition occurred from an over-shooting error to an undershooting error at a time that depended on the velocity of elbow rotation. 6. In a separate experiment, subjects were instructed to match either the perceived dynamic position or the perceived velocity of rotation imposed on the right elbow by actively rotating the left elbow. In both matching tasks, tendon vibration produced oppositely directed errors depending on the frequency of vibration. Vibration at 20 Hz produced a perception of decreased elbow velocity and a bias in dynamic position in the flexion direction, and vibration at 40 Hz produced the opposite perceptions. 7. We conclude that muscle spindle afferents, which are activated by tendon vibration, are an important source of the dynamic position and velocity information that the CNS uses to coordinate this movement sequence task. The observed effects of vibration timing and frequency suggest that perceptual changes evoked by vibration cannot be explained by the simple summation of sensory input evoked by movement and by vibration. Rather, the bias in perception produced by vibration appears to be related to the difference between vibration- and movement-evoked activity in muscle spindle afferents.     

New methodology applied to bonnet macaques (Macaca radiata) to address some contradictory evidence on manual asymmetries in old world monkeys.

Seven bonnet macaques (Macaca radiata) with strong hand preferences in performing a computer-generated joystick task that required directing a cursor to contact a small stationary target on a monitor were given comparable experience with each hand on the task over a 5-week period. Hand use was randomly restricted to either only the left or only the right hand across trials by automatically inputting into a computer the unique identification numbers of microchips implanted in the forearms of each macaque. Subsequent presentation of a novel task requiring maintenance of contact between a cursor and a moving target revealed no performance difference between preferred and nonpreferred hands or between left and right hands on the basis of number of errors or time to complete the task. The findings suggest that the strong hand preference for these tasks does not derive from a performance advantage for the preferred hand. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rate accuracy in handwheel cranking.

15 Ss cranked a handwheel, in a clockwise direction, at each of 5 rates of speed combined with each of 3 different handwheel radii; another 15 Ss cranked the same rate-radii; combinations counter-clockwise. The Ss were required to achieve the required rate by maintaining alignment between a target and indicator. At lower handwheel speeds, rate-accuracy improved with increases in the linear rate of movement for a constant angular rate; at higher angular speeds an inverse relationship appeared between linear rate and accuracy. For constant linear rates accuracy improved with increased angular rate up to about 175 rpm. No significant difference in accuracy appeared between the two directions of movement, but counterclockwise cranking resulted in significantly greater tendency to lag in rate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamical patterns in clapping behavior.

A nonlinear dynamics framework that has been applied successfully to several laboratory idealizations of rhythmic behaviors was applied to a more naturally occurring behavior, clapping. Inertial loading of limbs and frequency of oscillation were manipulated. Displacement of relative phase from perfectly in phase and the variability of relative phase, both of which are used as indexes of coordination dynamics, increased with greater inertial imbalance between limbs. Increasing frequency exaggerated these effects. These hallmark properties of coupled oscillator dynamics appeared whether or not the hands contacted, albeit with the latter condition revealing a significant asymmetry in the dynamics. Results highlight the generality of the coupled oscillator regime in interlimb coordination as well as its appropriateness for characterizing behaviors that involve contact of limb surfaces and suggest one way in which perceptual information may tune the dynamical regime. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On marching to two different drummers: Perceptual aspects of the difficulties.

Studied difficulty generating 2 responses that must follow different temporal sequences, unless the temporal patterns are simply related (e.g., periods on 2:1, 3:1 relation). For example, it is hard to tap to 2 conflicting rhythms presented concurrently (i.e., a polyrhythm) using the right and left hands or to tap while articulating a conflicting speech utterance. The present 3 experiments, with 55 undergraduates, showed that difficulties in processing conflicting rhythms occurred even when Ss were required to (a) merely monitor the stimuli and indicate the termination of 1 rhythmic sequence or (b) tap with a single hand. Responding to polyrhythms is thus difficult even without multiple limb coordination. Furthermore, the difficulty of 2-handed tapping to polyrhythms that involve 2 different tones decreased as the pitch difference between the tones was decreased. Results indicate that the difficulty of rhythmic coordination can be perceptually manipulated. Polyrhythmic performance thus provides an excellent opportunity for examining possible interactions of perceptual and motor organizations. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal and kinematic properties of motor behavior reflected in mentally simulated action.

Related perceptual, motor, and cognitive performances were examined to reveal the accuracy of the properties of action spontaneously represented when mentally simulating moving one's hand. The kinematic configuration of the body represented and transformed in mental simulations was not fixed or canonical but corresponded to one's current configuration. Mental simulation time mimicked movement time for natural efficient movement from a posture midway between each of the hand's joint limits into many other postures. Equal time was required for simulated and real movements into more common, comfortable postures. Shorter but proportional time was required for simulated movement than real movement into less common postures that involved longer trajectories, coordinated activity at more joints, motion near extremes of joint limits, and uncomfortable kinesthetic sensations. The findings suggest that sensorimotor structures support mental simulations of actions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brief bimanual force pulses: Correlations between the hands in force and time.

Three experiments assessed coupling phenomena in the coordination of bimanual force pulses. Experiment 1 required symmetric force pulses (equal target forces and rise times for both hands) using the index finger of each hand. As the authors expected, on the basis of bimanual pointing movement results, this experiment revealed positive correlations between both the force rise times and the force amplitudes of the two hands. Experiments 2 and 3 included asymmetric conditions with different target force amplitudes (Experiment 2) or target rise times (Experiment 3). In Experiment 2 force amplitudes but not rise times were fully decoupled in the asymmetric condition. In the asymmetric condition of Experiment 3, however, neither rise times nor force amplitudes were fully decoupled. The results suggest a hierarchical control structure with temporal control dominating nontemporal control of bimanual force coordination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The ratio of 2nd to 4th digit length: a predictor of sperm numbers and concentrations of testosterone, luteinizing hormone and oestrogen

The differentiation of the urinogenital system and the appendicular skeleton in vertebrates is under the control of Hox genes. The common control of digit and gonad differentiation raises the possibility that patterns of digit formation may relate to spermatogenesis and hormonal concentrations. This work was concerned with the ratio between the length of the 2nd and 4th digit (2D:4D) in humans. We showed that (i) 2D:4D in right and left hands has a sexually dimorphic pattern; in males mean 2D:4D = 0.98, i.e. the 4th digit tended to be longer than the 2nd and in females mean 2D:4D = 1.00, i.e. the 2nd and 4th digits tended to be of equal length. The dimorphism is present from at least age 2 years and 2D:4D is probably established in utero; (ii) high 2D:4D ratio in right hands was associated with germ cell failure in men (P = 0.04); (iii) sperm number was negatively related to 2D:4D in the right hand (P = 0.004); (iv) in men testosterone concentrations were negatively related to right hand 2D:4D and in women and men LH (right hand), oestrogen (right and left hands) and prolactin (right hand) concentrations were positively correlated with 2D:4D ratio and (v) 2D:4D ratio in right hands remained positively related to luteinizing hormone and oestrogen after controlling for sex, age, height and weight.