Richard G. Carson

Expressions of asymmetries and anchoring in bimanual coordination

Abstract The present study examined the contributions of inherent and incidental dynamical resources, and manual asymmetries, to the dynamics of bimanual coordination. Eight right-handed female subjects performed rhythmic movements of both hands, in two modes of coordination (in-phase and anti-phase), in self-paced and frequency-scaled conditions. In the in-phase (frequency-scaled) condition subjects were required to synchronize each beat of a metronome with either maximum pronation or maximum supination. In the anti-phase (frequency-scaled) condition subjects were required to synchronize each beat of the metronome with either maximum excursion to the left or maximum excursion to the right. Phase transitions from the anti-phase mode to the in-phase mode were observed as pacing frequency was increased. Transition pathways and times to transition onsets were dependent upon whether points of maximum pronation or maximum supination of the left or of the right hand were coincident with the metronome signal. The pattern of coordination (in-phase) adopted following phase transitions was predominantly that in which each beat of the metronome was syncronized with points of maximum pronation. A preliminary model accounting for these data is presented.

Phase transitions and critical fluctuations in rhythmic coordination of ipsilateral hand and foot

Four subjects performed rhythmic movements of the ankle and the wrist in time with an auditory metronome, in two modes of coordination, antiphase and in-phase. The forearm was placed in either a prone or a supine position. When movements were prepared in the antiphase mode, spontaneous transitions to the in-phase mode, or to phase wandering were observed as metronome frequency was increased. When prepared in the in-phase mode, transitions between in-phase modes or to phase wandering were occasionally observed. Predicted signature features of nonequilbrium phase transitions were noted, including loss of stability and critical fluctuations. The stability of the movement patterns was determined by spatial (dependent upon the direction of movement) rather than anatomical (dependent on the coupling of specific muscle groups) constraints. The position of the forearm had no consistent bearing upon the variability of the phase relations between the limbs, the frequency of phase transitions, or the time of onset of transitions. These results are discussed with reference to the coordination dynamics (e.g., multistability, loss of stability) of multijoint movements.

The contribution of vision to asymmetries in manual aiming.

An experiment was conducted to examine the hypothesis that the right hand system is superior in the processing of visual information. A manual aiming task utilizing four visual conditions was employed. In the full-vision (FV) condition subjects were afforded vision of both the hand and the target throughout the course of the movement. In the ambient-illumination-off (AO) condition, the room lights were extinguished at movement initiation, thus preventing vision of the moving limb. The target remained illuminated. In the target-off (TO) condition, the target was extinguished upon initiation of the movement. Ambient illumination and thus vision of the hand remained present. Finally there was a no-vision (NV) condition in which ambient illumination was removed and the target was extinguished upon initiation of the response movement. Although the manipulation of vision had potent effects upon terminal accuracy, and influenced reaction and movement time measures, the hands did not differ in the extent to which these characteristics were expressed. A left hand advantage for reaction time was observed. This may reflect a relative increase in right hemisphere involvement prior to aiming movements which are spatially complex.

Asymmetries in the Regulation of Visually Guided Aiming

An experiment was conducted to examine the contribution of sensory information to asymmetries in manual aiming. Movements were performed in four vision conditions. In the full-vision condition (FV), subjects were afforded vision of both the hand and the target throughout the course of the movement. In the ambient-illumination-off condition (AO), the room lights were extinguished at movement initiation, preventing vision of the moving limb. In the target-off (TO) condition, the target was extinguished upon initiation of the movement. In a no-vision (NV) condition, ambient illumination was removed and the target was extinguished upon initiation of the response movement. Results indicated that accuracy was superior in the full-vision and target-off conditions and when movements were made by the right hand. Movements made by the right hand were also of shorter mean duration. The magnitudes of performance asymmetries were uninfluenced by vision condition. Analyses of movement kinematics revealed that movements made in conditions in which there was vision of the limb exhibited a greater number of discrete modifications of the movement trajectory. On an individual-trial basis, no relationship existed between accuracy and the occurrence of discrete modifications. These data suggest that although vision greatly enhances accuracy, discrete modifications subserved by vision reflect the imposition of nonfunctional zero-order control processes upon continuous higher-order control regimes.

The Dynamical Substructure of Bimanual Coordination

Publisher Summary This chapter discusses the dynamical substructure of bimanual coordination. In undertaking dynamical analyses, a general problem is to obtain an appropriate level of description and identify the task-relevant degrees of freedom therein. The coupling of perception and action may itself be characterized as a pattern formation process. Characterization of the dynamics of the component oscillators may also elucidate features that are not adequately captured at the level of the collective variable. In a study described in the chapter, a number of preferred frequency trials were first performed to establish whether, in the absence of informational constraints, the degree of mechanical anchoring was equivalent in each portion of the movement cycle. The finding of preferred transition pathways between stationary states fulfills at least one of the predictions of symmetry-breaking dynamics. It also suggests that there may exist asymmetries that are not fully expressed in terms of unimanual preferred frequencies.

Asymmetries in the discrete and pseudocontinuous regulation of visually guided reaching

An experiment was conducted to examine the contribution of the hemispheres to the organization of aiming movements. The spatial positions of targets were obtained by extrapolating from brief visual displays of geometric patterns. The patterns comprised linear, quadratic, cubic, and quartic mathematical functions and varied in spatial complexity. Vision of the hand was also manipulated. While the hands did not differ in spatial accuracy, movements made by the right hand were of shorter duration and had higher peak velocities. The stimulus pattern strongly influenced kinematics, in particular the number of discrete modifications of the movement trajectory. Vision of the hand resulted in superior accuracy, although subjects were unable to compare the relative positions of the limb and the target. Vision of the hand did not lead to an increase in discrete adjustments, suggesting that visual information was used in a continuous fashion. Movements into ipsilateral space differed from those into contralateral space with respect to a number of parameters.

Manual asymmetries in the reproduction of a 3-dimensional spatial location.

Two experiments examined differences in the reproduction of preselected arm positioning movements. In Experiment 1, subjects defined a position in right space with a right index finger, or a position in left space with the left index finger, and then attempted to reproduce the position with either the left or the right hand. Subjects were more accurate when vision was available and when the reproduction hand was the same as the criterion hand. Availability of vision reduced the same hand advantage. There were no accuracy differences between the left and right hands. Experiment 2 was designed to determine whether the left-left and right-right criterion and reproduction advantages evident in the no vision condition of the first experiment were accounted for by the two movements being made by the same hand or by being performed in the same space. The results demonstrated that accuracy depended primarily on whether movements were made with the same hand. No right/left hand advantage was observed. The absence of a right hand advantage in either experiment may be due to the spatial complexity of the task examined or to the relative absence of any temporal constraints.

The role of impulse variability in manual-aiming asymmetries

SummaryTwo experiments are reported in which we examined the hypothesis that the advantage of the right hand in target aiming arises from differences in impulse variability. Subjects made aiming movements with the left and right hands. The force requirements of the movements were manipulated through the addition of mass to the limb (Experiments 1 and 2) and through control of movement amplitude (Experiment 1). Although the addition of mass diminished performance (i. e., it increased movement times in Experiment 1 and increased error in Experiment 2), the two hands were not differently affected by the manipulation of required force. In spite of the fact that the right hand exhibited enhanced performance (i. e., lower movement times in Experiment 1 and greater accuracy in Experiment 2), these advantages were not reflected in kinematic measures of impulse variability.

Chapter 3 Visual Feedback Processing and Manual Asymmetries: An Evolving Perspective1

Publisher Summary This chapter focuses on the evolution of visual feedback processing and manual asymmetries. The “feedback processing hypothesis” proposes that manual asymmetries are a function of the differential efficiencies with which sensory feedback is processed by the hand-hemisphere systems. In particular, the preferred hand is thought to be associated with a neural substrate, which may more effectively use sensory information to effect “on-line” modifications required for accurate aiming responses. The proposal that the hands differ in the efficiency with which feedback is processed has recently been explicitly interpreted as a suggestion that the right hand/left hemisphere is superior in the processing of visual information. This position has the virtue of being clearly defined and thus amenable to testing. A series of attempts have been made to map what are presumed to be the information processing characteristics of the cerebral hemispheres onto variables, which ostensibly capture the essential aspects of movement regulation. There are both general and specific problems associated with this approach.

Chapter 10 Asymmetries in the dynamics of interlimb coordination

Two experiments were conducted to examine whether asymmetries in cortical organization with respect to timing functions are expressed in the dynamics of self paced, and externally paced, rhythmic coordination tasks. Four subjects performed movements of the ankle and the wrist, in two modes of coordination, anti-phase and in-phase. In Experiment 1, subjects conducted these movements at their preferred frequencies. In Experiment 2 their movements were paced by an auditory metronome at 1 Hz and 2 Hz. Coordination dynamics were examined at both the kinematic (Experiments 1 & 2) and the neuromuscular (Experiment 1) levels of observation. When self-paced, movements of the left side were more variable with respect to oscillation frequency than movements of the right side. Uniformity of the order parameter, relative phase, was also greater for movements of the right side. These differences were eliminated when movements were externally paced.