Jean-Jacques Temprado

The interplay of attention and bimanual coordination dynamics.

Despite their common origin, studies on motor coordination and on attentional load have developed into separate fields of investigation, bringing out findings, methods, and theories which are diverse if not mutually exclusive. Sitting at the intersection of these two fields, this article addresses the issue of behavioral flexibility by investigating how intention modifies the stability of existing patterns of coordination between moving limbs. It addresses the issue, largely ignored until now, of the attentional cost incurred by the central nervous system (CNS) in maintaining a coordination pattern at a given level of stability, in particular under different attentional priority requirements. The experimental paradigm adopted in these studies provides an original mix of a classical measure of attentional load, namely, reaction time, and of a dynamic approach to coordination, most suitable for characterizing the dynamic properties of coordinated behavior and behavioral change. Findings showed that central cost and pattern stability covary, suggesting that bimanual coordination and the attentional activity of the CNS involved in maintaining such a coordination bear on the same underlying dynamics. Such a conclusion provides a strong support to a unified approach to coordination encompassing a conceptualization in terms of information processing and another, more recent framework rooted in self-organization theories and dynamical systems models.

Effects of attention on phase transitions between bimanual coordination patterns: a behavioral and cost analysis in humans

The present study aimed to obtain a behavioral analysis of the effects of attentional focus on the dynamics of phase transitions in bimanual coordination and to evaluate the central cost expended by the central nervous system to maintain and stabilize such coordination patterns before and after the transition. Eight subjects were asked to execute an anti-phase coordination pattern (180 degrees of relative phase), while gradually increasing the frequency of oscillation. The central cost was assessed using a dual-task paradigm associating the bimanual coordination task with a reaction time task. Results showed that: (1) the transition process was significantly altered by focusing attention on the bimanual coordination task; and (2) the cost involved in sustaining the bimanual patterns was determined by their coordination dynamics.

Shared dynamics of attentional cost and pattern stability

This paper examines the informational activity devoted by the CNS to couple oscillating limbs in order to sustain and stabilize bimanual coordination patterns. Through a double-task paradigm associating a bimanual coordination task and a reaction time (RT) task, we investigated the relation between the stability of preferred bimanual coordination patterns and the central cost expended by the CNS for their stabilization. Ten participants performed in-phase and anti-phase coordination patterns in a dual task condition (coordination + RT) at several frequencies (0.5, 0.75, 1.0, 1.5, and 2.0 Hz), thereby decreasing the stability of the bimanual patterns. Results showed a U-shaped evolution of pattern stability and attentional cost, as a function of oscillation frequency, exhibiting a minimum value at the same frequency. These findings indicate that central cost and pattern stability covary and may share common, high order dynamics. Moreover, the attentional focus given to the bimanual coordination and the RT task was also manipulated by requiring either shared attention or priority to the coordination task. Such a manipulation led to a tradeoff between pattern stability and RT performance: The more stable the pattern, the more costly it is to stabilize. This suggests that stabilizing a coordination pattern incurs a central cost that depends on its intrinsic stability. Conceptual consequences of these results for understanding the relationship between attention and coordination are drawn, and the mechanisms putatively at work in dual tasks are discussed.

A dynamical framework to understand performance trade-offs and interference in dual tasks.

This study demonstrated that the dynamic pattern approach may reconcile resource and outcome conflict theories to explain performance in dual tasks. Participants performed a bimanual coordination task and a reaction time task with different conditions of attentional priority. Results showed a trade-off between pattern variability and reaction time when priority was given to the coordination task. Such a trade-off was indicative of resource allocation. An analysis of perturbation in the bimanual coordination revealed interference, a reputed sign of outcome conflict. Moreover, interference diminished substantially when priority was given to the bimanual task. The coexistence of performance trade-off and outcome conflict suggests that these two phenomena are not mutually exclusive. Rather, both may follow from modifying the coupling between the limbs through attention.

Attentional demands reflect learning-induced alterations of bimanual coordination dynamics

This study aimed to investigate the effects of practice on bimanual coordination dynamics and attentional demands. Participants were asked to perform a dual‐task associating a cyclic antiphase bimanual pattern and a discrete reaction time task. A pretest determined each individual critical transition frequency. In the training session, participants practised 120 trials. They were instructed to maintain the antiphase coordination pattern at the critical transition frequency. The training session was interrupted and followed by an intermediate test (after 60 trials) and a post‐test (30 min after 120 trials), respectively. A retention test was performed 7 days after the end of the training session. Results showed that: (i) the number of transitions decreased as a consequence of practice; and (ii), subjects were able to maintain the antiphase pattern at a higher frequency than in the pretest. Analysis of the trade‐off between relative phase variability and reaction time showed that participants were able to maintain a higher level of stability at the same (intermediate and post‐test) or a lower attentional cost (retention test). These findings show that phase transition dynamics and pattern stability can be significantly modified as a result of practice. Changes in the trade‐off between pattern stability and cost with learning confirm that the attentional cost incurred by the central nervous system to maintain pattern stability decreased with practice. In line with recent neurobiological studies, the present study provides new insights regarding relationships between brain processes, attentional demands and coordinated behaviour in learning bimanual patterns.

Aging induced loss of complexity and dedifferentiation: consequences for coordination dynamics within and between brain, muscular and behavioral levels

Growing evidence demonstrates that aging not only leads to structural and functional alterations of individual components of the neuro-musculo-skeletal system (NMSS) but also results in a systemic re-organization of interactions within and between the different levels and functional domains. Understanding the principles that drive the dynamics of these re-organizations is an important challenge for aging research. The present Hypothesis and Theory paper is a contribution in this direction. We propose that age-related declines in brain and behavior that have been characterized in the literature as dedifferentiation and the loss of complexity (LOC) are: (i) synonymous; and (ii) integrated. We argue that a causal link between the aforementioned phenomena exists, evident in the dynamic changes occurring in the aging NMSS. Through models and methods provided by a dynamical systems approach to coordination processes in complex living systems, we: (i) formalize operational hypotheses about the general principles of changes in cross-level and cross-domain interactions during aging; and (ii) develop a theory of the aging NMSS based on the combination of the frameworks of coordination dynamics (CD), dedifferentiation, and LOC. Finally, we provide operational predictions in the study of aging at neural, muscular, and behavioral levels, which lead to testable hypotheses and an experimental agenda to explore the link between CD, LOC and dedifferentiation within and between these different levels.

Aging of sensorimotor processes: a systematic study in Fitts’ task

Though age-related decrease in information-processing capacities is hypothesized to be a prominent cause of behavioral slowing, it has been scarcely systematically studied in goal-directed motor tasks. The present study investigated how the decrease in information processing affects the sensorimotor processes underlying the control of a discrete Fitts’ task. The index of difficulty (ID) of the task was manipulated using changes in either target distance (D) or target width (W). In each manipulation, movement (MTs), acceleration (ATs) and deceleration times (DTs) of young and older participants were compared across eight ID levels. They were analyzed with efficiency functions, state traces and Brinley plots. Our results showed that older participants were always slower. However, in both age groups, MTs were longer in D manipulation, which resulted from a slowing of both ATs and DTs, while W manipulation affected mainly DTs. In D manipulation, equivalent age-related slowing ratios were observed for AT and DT (1.3). In W manipulation, ATs of older participants were additively slower than those of young participants. Conversely, DTs presented a multiplicative slowing ratio of 1.3. These findings showed that ID manipulations differentially loaded information processing in the nervous system and that age-related slowing of multisensory control processes was independent of the manipulated dimension. Nevertheless, ID manipulations revealed different age-related adaptations to task constraints, suggesting that D and W manipulations are complementary means to assess age-related slowing of the processes involved in target-directed rapid-aiming tasks, with D scaling being more specific to capture the slowing of force-impulse control.

The coalition of constraints during coordination of the ipsilateral and heterolateral limbs.

Previous work on the coordination between the upper and lower limbs has invariably shown that its accuracy/stability is primarily determined by the mutual direction between limbs in extrinsic space and not by muscle relationships. Here we show that muscle grouping does play a critical role in coordination of the arm and leg, in addition to direction. More specifically, the simultaneous activation of isofunctional muscles and/or limb movements proceeding in the same direction, results in more successful performance than the alternated activation of isofunctional muscles and/or movements occurring in different directions. In the absence of isofunctional muscle coupling, the mutual direction between the limbs plays a more prominent role in determining coordinative accuracy. These coordination constraints can largely account for the observed differences between ipsilateral and heterolateral limb coordination. The findings are discussed in view of the coalition of coordination constraints.

Plane of Motion Mediates the Coalition of Constraints in Rhythmic Bimanual Coordination

The authors hypothesized that the modulation of coordinative stability and accuracy caused by the coalition of egocentric (neuromuscular) and allocentric (directional) constraints varies depending on the plane of motion in which coordination patterns are performed. Participants (N = 7) produced rhythmic bimanual movements of the hands in the sagittal plane (i.e., up-and-down oscillations resulting from flexion—extension of their wrists). The timing of activation of muscle groups, direction of movements, visual feedback, and across-trial movement frequency were manipulated. Results showed that both the egocentric and the allocentric constraints modulated pattern stability and accuracy. However, the allocentric constraint played a dominant role over the egocentric. The removal of vision only slightly destabilized movements, regardless of the effects of directional and (neuro)muscular constraints. The results of the present study hint at considering the plane in which coordination is performed as a mediator of the coalition of egocentric and allocentric constraints that modulates coordinative stability of rhythmic bimanual coordination.

Bimanual training in stroke: How do coupling and symmetry-breaking matter?

BackgroundThe dramatic consequences of stroke on patient autonomy in daily living activities urged the need for new reliable therapeutic strategies. Recently, bimanual training has emerged as a promising tool to improve the functional recovery of upper-limbs in stroke patients. However, who could benefit from bimanual therapy and how it could be used as a part of a more complete rehabilitation protocol remain largely unknown. A possible reason explaining this situation is that coupling and symmetry-breaking mechanisms, two fundamental principles governing bimanual behaviour, have been largely under-explored in both research and rehabilitation in stroke.DiscussionBimanual coordination emerges as an active, task-specific assembling process where the limbs are constrained to act as a single unit by virtue of mutual coupling. Consequently, exploring, assessing, re-establishing and exploiting functional bimanual synergies following stroke, require moving beyond the classical characterization of performance of each limb in separate and isolated fashion, to study coupling signatures at both neural and behavioural levels. Grounded on the conceptual framework of the dynamic system approach to bimanual coordination, we debated on two main assumptions: 1) stroke-induced impairment of bimanual coordination might be anticipated/understood by comparing, in join protocols, changes in coupling strength and asymmetry of bimanual discrete movements observed in healthy people and those observed in stroke; 2) understanding/predicting behavioural manifestations of decrease in bimanual coupling strength and/or increase in interlimb asymmetry might constitute an operational prerequisite to adapt therapy and better target training at the specific needs of each patient. We believe that these statements draw new directions for experimental and clinical studies and contribute in promoting bimanual training as an efficient and adequate tool to facilitate the paretic upper-limb recovery and to restore spontaneous bimanual synergies.SummarySince bimanual control deficits have scarcely been systematically investigated, the eventual benefits of bimanual coordination practice in stroke rehabilitation remains poorly understood. In the present paper we argued that a better understanding of coupling and symmetry-breaking mechanisms in both the undamaged and stroke-lesioned neuro-behavioral system should provide a better understanding of stroke-related alterations of bimanual synergies, and help clinicians to adapt therapy in order to maximize rehabilitation benefits.