Effects of movement stability and congruency on the emergence of spontaneous interpersonal coordination

The current project evaluated the relationship between the stability of intrapersonal coordination and the emergence of spontaneous interpersonal coordination. Participants were organized into pairs, and each participant was instructed to produce either an inphase or antiphase pattern of intrapersonal bimanual coordination using two hand-held pendulums, while simultaneously performing an interpersonal puzzle task. At issue was whether the emergence and stability of spontaneous interpersonal rhythmic coordination is influenced by ("Experiment 1") the stability of the intrapersonal coordination patterns produced by co-actors and ("Experiment 2") the congruency of the intrapersonal coordination patterns produced by co-actors. The stability of intrapersonal movement coordination did not affect the emergence of spontaneous interpersonal coordination. The degree of interpersonal coordination observed was similar when both participants in a pair produced either inphase or antiphase patterns of intrapersonal bimanual coordination. Moreover, the congruency of the intrapersonal coordination patterns only slightly affected the emergence of interpersonal coordination, with only marginally lower inphase interpersonal entrainment when participants produced incongruent patterns of intrapersonal coordination (e.g., inphase-antiphase). Interestingly, movement observation and the emergence of interpersonal coordination did not affect the stability of intrapersonal bimanual coordination. The results suggest that interlimb rhythmic bimanual coordination reflects a single intrapersonal perceptual-motor synergy and that these bimanual synergies (not individual limbs) are what become spontaneously entrained interpersonally.     

Interpersonal Fitts�� law: when two perform as one

Intra- and interpersonal coordination was investigated using a bimanual Fitts' law task. Participants tapped rhythmically between pairs of targets. Tapping was performed with one hand (unimanual), two hands (intrapersonal coordination), and one hand together with another participant (interpersonal coordination). The sizes and distances of targets in a pair were manipulated independently for each hand. When target difficulty was unequal across hands, movement times were similar in the coordination conditions, in violation of Fitts' law. Processing speed (measured by index of performance) increased for more difficult tasks, suggesting increased attention, even for dyads. These findings suggest that similar processes, not captured by centralized control, guide coordination for both individuals and dyads. Measures of coordination, though, still showed stronger coordination tendencies for intrapersonal coordination, indicating a possible role for centralized mechanisms.     

Sharing a bimanual task between two: evidence of temporal alignment in interpersonal coordination

In recent years, researchers have made many new discoveries in the field of social interaction and have attempted to understand the mechanisms of interpersonal coordination. This research is marked by two streams: On the one hand, there are attempts to explain spontaneous, incidental interpersonal coordination in terms of the behavioral dynamics perspective, and on the other, to explain instructed, intentional interpersonal coordination in terms of joint action. Other paradigms fall somewhere between incidental and intentional coordination, e.g. task sharing paradigms. The present study has two major objectives. First, we wanted to explore to what extent a dyadic scenario for bimanual coordination mimics typical signatures of bimanual coordination performance as obtained in the classical individual scenario. Second, if such mimicking is obtained, we wanted to investigate the kind of information on which the coordination between the two individuals may be grounded. To do so, we used a bimanual aiming task, which enabled us to assess measurements of two levels of coordination: global (operating over longer periods of time) and local (operating on each particular trial). In Experiment 1, this task was performed in an individual and in a dyadic setting. In the dyadic scenario, we observed strong global coordination and weak local coordination. In Experiment 2, we replicated this pattern and showed that different kinds of feedback had no impact on interpersonal coordination. Based on these findings, we propose that interpersonal coordination in a non-rhythmic choice response task is based on weak interpersonal coordination.     

Effects of varying task constraints on solutions to joint coordination in a sit-to-stand task

The question of how multijoint movement is controlled can be studied by discovering how the variance of joint trajectories is structured in relation to important task-related variables. In a previous study of the sit-to-stand task, for instance, variations of body segment postures that leave the position of the body's center of mass (CM) unchanged were significantly greater than variations of body segment posture that varied the CM position. The present experiments tested the hypothesis that such structuring of joint configuration variability is accentuated when the mechanical or perceptual task demands are made more challenging. Six subjects performed the sit-to-stand task without vision (eyes closed), either on a normal or on a narrow support surface. An additional constraint on the postural task was introduced in a third condition by requiring subjects to maintain light touch (less than 1 N) with the fingertips while coming to a standing position on the narrow base of support. The joint configurations observed at each point in normalized time were analyzed with respect to trial-to-trial variability. The task variables CM and head position were used to define goal-equivalent sets of joint configurations ("uncontrolled manifolds," UCMs) within which variation of joint configuration leaves the task variables unchanged. The variability of joint configurations across trials was decomposed into components that did not affect (within the UCM) and that did affect (orthogonal to the UCM) the values of these task variables. Our results replicate the earlier finding of much larger variability in directions of joint space that leave the CM unchanged compared with directions that affect CM position. This effect was even more pronounced here than in the previous experiment, probably because of the more difficult perceptual conditions in the current study (eyes closed). When the mechanical difficulty of the task was increased, the difference between the two types of joint variability was further accentuated, primarily through increase in goal-equivalent variance. This provides evidence for the hypothesis that under challenging task constraints increased variability is selectively directed into task-irrelevant degrees of freedom. Because differential control along different directions of joint space requires coordination among joint angles, this observation supports the view that the CNS responds to increased task difficulty through enhanced coordination among degrees of freedom. The adaptive nature of this coordination is further illustrated by the similar enhanced use of goal-equivalent joint combinations to achieve a stable CM position when subjects stood up under the additional constraint of maintaining light touch with the fingertips. This was achieved by channeling goal-equivalent variability into different directions of joint configuration space.     

Making oneself predictable: reduced temporal variability facilitates joint action coordination

Performing joint actions often requires precise temporal coordination of individual actions. The present study investigated how people coordinate their actions at discrete points in time when continuous or rhythmic information about others' actions is not available. In particular, we tested the hypothesis that making oneself predictable is used as a coordination strategy. Pairs of participants were instructed to coordinate key presses in a two-choice reaction time task, either responding in synchrony (Experiments 1 and 2) or in close temporal succession (Experiment 3). Across all experiments, we found that coactors reduced the variability of their actions in the joint context compared with the same task performed individually. Correlation analyses indicated that the less variable the actions were, the better was interpersonal coordination. The relation between reduced variability and improved coordination performance was not observed when pairs of participants performed independent tasks next to each other without intending to coordinate. These findings support the claim that reducing variability is used as a coordination strategy to achieve predictability. Identifying coordination strategies contributes to the understanding of the mechanisms involved in real-time coordination.     

Prehension movements in the macaque monkey: effects of object size and location

Prehension movements were examined in freely behaving monkeys and compared with the well-known characteristics of human movements. The degree of independence of the components of movements (i.e., reaching and grasping) was investigated in animals trained to reach for and grasp three-dimensional objects. To this aim, the kinematics of prehension movements was recorded using an Optotrak system in two tasks. In one task, monkeys grasped a small or a large object (size task), in the other, they grasped an object of constant size placed at three different spatial locations (location task). We found that object size and its location affected both reaching and grasping. In particular, in the size task, we found that the maximum grip aperture strongly depended on the selection of the grip and not only on the size of an object. Our results also revealed that, in monkeys as well as in humans, the reaching parameters are highly sensitive to task-related constraints such as accuracy demands. The results of the location task showed a difference between rightward and leftward movements, a pattern of grip aperture that varied across animals, and a large degree of coordination between the two components. These findings argue against a strict postulate of independence between the visuo-motor channels, favoring instead the idea of variable degrees of coordination between the reach and grasp components depending on the task demands. Finally, this work emphasizes the relevance of studying monkey's prehension movements as a useful step to the understanding of visuo-motor control in humans.     

Effects of interlimb and intralimb constraints on bimanual shoulder-elbow and shoulder-wrist coordination patterns

The present study addressed the interactions between interlimb and intralimb constraints during the control of bimanual multi-joint movements. Participants performed eight coordination tasks involving bilateral shoulder-elbow (expt I) and shoulder-wrist (expt II) movements. Three principal findings were obtained. First, the principle of muscle homology (in-phase coordination), giving rise to mirror symmetrical movements with respect to the midsagittal plane, had a powerful influence on the quality of interlimb coordination. In both experiments, the accuracy and stability of inter- and/or intralimb coordination deteriorated as soon as the antiphase mode was introduced in one or both joint pairs. However, the mutual influences between bilateral distal and proximal joint pairs varied across coordination tasks and effectors. Second, the impact of intralimb coordination modes on the quality of intralimb coordination was inconsistent between adjacent (expt I) and non-adjacent joint (expt II) combinations. Third, the mode of interlimb coordination affected the quality of intralimb coordination, whereas strong support for the converse effect was not obtained. Taken together, these observations point to a hierarchical control structure whereby interlimb coordination constraints have a stronger impact on the global coordination of the system than intralimb constraints, whose impact is substantially dependent on effector and task. The finding that intralimb coordination is subordinate to interlimb coordination during the production of bimanual multi-joint coordination patterns indicates that symmetry is a major organizational principle in the neural control of complex movement.     

Comparing the attractor strength of intra- and interpersonal interlimb coordination using cross-recurrence analysis

Previous research has demonstrated that intra- and interpersonal rhythmic interlimb coordination are both constrained by the self-organizing entrainment process of coupled oscillators. Despite intra- and interpersonal coordination exhibiting the same stable macroscopic movement patterns the variability of the coordination is typically found to be much greater for inter- compared to intrapersonal coordination. Researchers have assumed that this is due to the interpersonal visual-motor coupling producing a weaker attractor dynamic than the intrapersonal neuromuscular coupling. To determine whether this assumption is true, two experiments were conducted in which pairs of participants coordinated hand-held pendulums swung about the wrist, either intra- and interpersonally. Using the cross-recurrence statistics of percent recurrence and maxline to independently index the level of noise and the attractor strength of the coordination, respectively, the results confirmed that the attractor strength was significantly weaker for inter- compared to intrapersonal coordination and that a similar magnitude of noise underlies both.     

Change of a motor synergy for dampening hand vibration depending on a task difficulty

The present study investigated the relationship between the number of usable degrees of freedom (DOFs) and joint coordination during a human-dampening hand vibration task. Participants stood on a platform generating an anterior–posterior directional oscillation and held a water-filled cup. Their usable DOFs were changed under the following conditions of limb constraint: (1) no constraint; (2) ankle constrained; and (3) ankle–knee constrained. Kinematic whole-body data were recorded using a three-dimensional position measurement system. The jerk of each body part was evaluated as an index of oscillation intensity. To quantify joint coordination, an uncontrolled manifold (UCM) analysis was applied and the variance of joints related to hand jerk divided into two components: a UCM component that did not affect hand jerk and an orthogonal (ORT) component that directly affected hand jerk. The results showed that hand jerk when the task used a cup filled with water was significantly smaller than when a cup containing stones was used, regardless of limb constraint condition. Thus, participants dampened their hand vibration utilizing usable joint DOFs. According to UCM analysis, increasing the oscillation velocity and the decrease in usable DOFs by the limb constraints led to an increase of total variance of the joints and the UCM component, indicating that a synergy-dampening hand vibration was enhanced. These results show that the variance of usable joint DOFs is more fitted to the UCM subspace when the joints are varied by increasing the velocity and limb constraints and suggest that humans adopt enhanced synergies to achieve more difficult tasks.     

Visual influences on postural and manual interpersonal coordination during a joint precision task

We investigated whether the interpersonal postural coordination that occurs during a joint supra-postural, manual precision task is driven by the constraints of the task, or, instead results from visual entrainment to the movements of a co-actor. Participants were instructed to coordinate their finger movements under conditions where participants could see others’ whole-body movements or could only see the results of the other’s actions. Participants’ finger and torso movements were recorded. Coordination was quantified using cross-recurrence quantification analysis measures. Interpersonal coordination was enhanced by, although it did not depend entirely upon, visual information about the co-actor’s body movements.     

Is there a specific executive capacity for dual task coordination? Evidence from Alzheimer's disease

Three experiments compared groups of Alzheimer's disease (AD) patients and healthy older and younger participants on visuospatial tracking and digit sequence recall, as single tasks and performed concurrently. In Experiment 1, tasks were performed concurrently with very low demand relative to span. Only the AD patients showed a dual task deficit. In Experiment 2, single task demand was manipulated on each task from below span to above span for each individual. All groups showed the same performance reductions with increasing demand. In Experiment 3, demand on 1 task was constant, whereas demand on the concurrent task was varied. AD patients showed a clear dual task deficit but were no more sensitive than control groups to varying demand. Results suggest an identifiable cognitive resource for dual task coordination within a multiple component working memory system.     

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.     

Effects of hand termination and accuracy constraint on eye–hand coordination during sequential two-segment movements

The purpose of this study was to examine the effects of accuracy constraints and termination requirements of hand movement on eye-hand coordination. Healthy adults performed two-segment eye and hand aiming movements to predetermined stationary targets. While two-segment eye movements were made to the first and second targets for all conditions, hand movements were varied across conditions. The first segment had two target sizes to alter accuracy constraints. There were three hand movement types with different termination requirements: (1) stop both at the first and at the second targets, (2) stop at the first target and discontinue, and (3) move through the first target and discontinue. The results showed that the initiation of saccades was moderately correlated with the initiation of hand movements, and both initiations changed in a similar fashion depending on various hand termination requirements. Amplitude of primary saccades and frequency of corrective saccades during the first segment were affected by the combined effects of accuracy constraints and hand termination requirements. These results suggest that the planning and execution of saccades are based in part on global task constraints related to the accuracy and termination demands of hand movements over the two segments. During the transition from the first to the second segment, the gaze was held on the first target until shortly after the pointing to that target was terminated, showing gaze anchoring. The gaze anchoring was prolonged due to the increased accuracy constraint of that target or by including pointing to the second target. However, the gaze anchoring was broken prior to the completion of pointing when the accuracy constraint was reduced and pointing to the second target was excluded. The observed modifications of gaze anchoring imply that the oculomotor system is functionally obligated to fixate a gaze to a pointing target only to the extent that successful completion of a pointing task is ensured by the actual completion or by a predictive assessment of pointing termination.     

Facilitation and interference components in the joint Simon task

Two experiments were conducted to assess whether the joint Simon effect is composed of facilitation and interference and whether facilitation is increased by a joint spatially compatible practice performed before performing the joint Simon task. In both experiments, participants were required to perform a Simon task along another person. Trials could be corresponding, non-corresponding, and neutral. In Experiment 1, participants performed only the Simon task. In Experiment 2, participants first practiced on a joint spatial compatibility task with a compatible mapping and, after a 5-min delay, transferred to a joint Simon task. Results indicated that the joint Simon effect consisted primarily of interference, which was significantly increased by a spatially compatible practice performed jointly. These results allow us to better define in what ways the presence of the other influences performance, in showing that when participants perform a task along with another individual, they display a disadvantage (i.e., slower RTs) when they have to respond to stimuli appearing on the other agent's side.     

The effect of warning stimulus modality on blink startle modification in reaction time tasks

The present study investigated the effects of lead stimulus modality on modification of the acoustic startle reflex during three reaction time tasks. In Experiment 1, participants (N = 48) were required to press a button at the offset of one stimulus (task relevant) and to ignore presentations of a second (task irrelevant). Two tones that differed in pitch or two lights served as signal stimuli. Blink startle was elicited during some of the stimuli and during interstimulus intervals. Skin conductance responses were larger during task-relevant stimuli in both groups. Larger blink facilitation during task-relevant stimuli was found only in the group presented with auditory stimuli, whereas larger blink latency shortening during task-relevant stimuli was found in both groups. Experiment 2 (N = 32) used only a task-relevant stimulus. Blink magnitude facilitation was significant only in the group presented with tones, whereas blink latency shortening was significant in both groups. Experiment 3 (N = 80) used a go/nogo task that required participants to press a button if one element of a compound stimulus ended before the second, but not if the asynchrony was reversed. The offset asynchrony was varied between groups as a manipulation of task difficulty. Startle magnitude facilitation was larger during acoustic than during visual stimuli and larger in the easy condition. The present data indicate that startle facilitation in a reaction time task is affected by stimulus modality and by task demands. The effects of the task demands seem to be independent of lead stimulus modality.     

Attentional blink reflex modulation in a continuous performance task is modality specific

Four experiments investigated the attentional modulation of acoustic blinks during continuous spatial tracking tasks. Experiment 1 found blink magnitude inhibition in a visual tracking task. Experiment 2 replicated this finding and also found blink latency slowing. Experiment 3 varied the difficulty of the task and found larger blink inhibition in the easy condition. Blink latency slowing did not differ and was significant at both difficulty levels. Experiment 4 employed less difficult visual and acoustic tracking tasks at two levels of task load. Blink magnitude inhibition during the visual and facilitation during the acoustic task was significant during high load in both modality groups. Blink latency was slowed in all visual task conditions and shortened in the difficult acoustic task. These results indicate that attentional blink modulation in a continuous spatial tracking task is modality specific.     

Interplay of biomechanical and neuromuscular constraints on pattern stability and attentional demands in a bimanual coordination task in human subjects

Recent debate has focused upon the issue of whether general principles and laws of movement coordination may be derived without reference to anatomical, mechanical and physiological mechanisms. It has been proposed that self-generated movement involves the interaction of biomechanical and neuromuscular constraints. Biomechanical constraints are usually considered of as arising from the pendular dimensions of the limb or limb segments whereas neuromuscular constraints are commonly associated with nervous and metabolic control processes. The present study aims to investigate the interplay between these two different constraints on bimanual pattern stability and attentional demands. Five subjects were asked to execute an anti-phase coordination pattern (180 degrees of relative phase), while gradually increasing the frequency of oscillation and changing the rotational inertia of the joysticks. Frequency manipulation was expected to affect the neuromuscular constraints. Inertial manipulation was expected to affect biomechanical constraints. Attentional demands, reflecting the central cost associated with the maintenance of the coordination pattern was assessed using a dual-task paradigm. The results showed that: (1) increasing the oscillation frequency altered both coordination dynamics and attentional demands associated with the maintenance of bimanual coordination patterns; (2) manipulation of rotational inertia of the joysticks also altered pattern stability (standard deviation of relative phase) and coordination dynamics (i.e. the number of phase transition and the before transition), but these alterations were not paralleled by a change in attentional demands.     

Inner speech is used to mediate short-term memory, but not planning, among intellectually high-functioning adults with autism spectrum disorder

Evidence regarding the use of inner speech by individuals with autism spectrum disorder (ASD) is equivocal. To clarify this issue, the current study employed multiple techniques and tasks used across several previous studies. In Experiment 1, participants with and without ASD showed highly similar patterns and levels of serial recall for visually presented stimuli. Both groups were significantly affected by the phonological similarity of items to be recalled, indicating that visual material was spontaneously recoded into a verbal form. Confirming that short-term memory is typically verbally mediated among the majority of people with ASD, recall performance among both groups declined substantially when inner speech use was prevented by the imposition of articulatory suppression during the presentation of stimuli. In Experiment 2, planning performance on a tower of London task was substantially detrimentally affected by articulatory suppression among comparison participants, but not among participants with ASD. This suggests that planning is not verbally mediated in ASD. It is important that the extent to which articulatory suppression affected planning among participants with ASD was uniquely associated with the degree of their observed and self-reported communication impairments. This confirms a link between interpersonal communication with others and intrapersonal communication with self as a means of higher order problem solving.     

The joint flanker effect: sharing tasks with real and imagined co-actors

The Eriksen flanker task (Eriksen and Eriksen in Percept Psychophys 16:143-149, 1974) was distributed among pairs of participants to investigate whether individuals take into account a co-actor's S-R mapping even when coordination is not required. Participants responded to target letters (Experiment 1) or colors (Experiment 2) surrounded by distractors. When performing their part of the task next to another person performing the complementary part of the task, participants responded more slowly to stimuli containing flankers that were potential targets for their co-actor (incompatible trials), compared to stimuli containing identical, compatible, or neutral flankers. This joint Flanker effect also occurred when participants merely believed to be performing the task with a co-actor (Experiment 3). Furthermore, Experiment 4 demonstrated that people form shared task representations only when they perceive their co-actor as intentionally controlling her actions. These findings substantiate and generalize earlier results on shared task representations and advance our understanding of the basic mechanisms subserving joint action.     

Posture control development in children aged 2-7 years old, based on the changes of repeatability of the stability indices

Precision manual tasks require a stable postural background which might be facilitated by respiratory modulations. We investigated the influence of performing a manual precision aiming task on respiratory rate and dynamics, and the coherence between respiration and center of pressure (COP) fluctuations (i.e., the postural-respiratory synergy). Participants aimed a pointer at targets of different sizes while seated or standing. Respiratory rate increased during the aiming period compared to a pre-task phase, but did not vary as a function of aiming difficulty. Recurrence quantification analysis revealed an increased incidence of slowly changing periods of chest movements during the most difficult aiming condition, which required the highest level of manual precision. Aiming, irrespective of difficulty, led to increases in the regularity of the respiratory pattern. Increases in respiratory rate during aiming were accompanied by an increased level of coherence for the seated but not the standing posture, suggesting that task demands affect the organization of coordination across the postural-respiratory synergy. Functional demands of the task likely shape the effectiveness of compensation for respiration during precision aiming.