Robrecht P. R. D. van der Wel

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.

Hand path priming in manual obstacle avoidance: evidence for abstract spatiotemporal forms in human motor control.

Previous research suggests that motor equivalence is achieved through reliance on effector-independent spatiotemporal forms. Here the authors report a series of experiments investigating the role of such forms in the production of movement sequences. Participants were asked to complete series of arm movements in time with a metronome and, on some trials, with an obstacle between 1 or more of the target pairs. In moves following an obstacle, participants only gradually reduced the peak heights of their manual jumping movements. This hand path priming effect, scaled with obstacle height, was preserved when participants cleared the obstacle with 1 hand and continued with the other, and it was modulated by future task demands. The results are consistent with the hypothesis that the control of movement sequences relies on abstract spatiotemporal forms. The data also support the view that motor programming is largely achieved by changing just those features that distinguish the next movement to be made from the movement that was just made.

Moving the arm at different rates: slow movements are avoided.

ABSTRACT Qualitative and quantitative changes characterize locomotion and rhythmic interlimb coordination at different speeds. Legs and hands do not move more or less quickly; they also adopt different relative coordination patterns. In the present article, the authors asked whether similar transitions occur for unimanual hand movements when speed is slowed below the preferred speed. Participants moved a handheld dowel back and forth between 2 large circular targets in time with a metronome at periods between 370 ms and 1667 ms. The authors analyzed the kinematics of participants’ movements at each period and found that proportional dwell time and number of peaks in the velocity profile increased as driving periods increased. Path lengths and peak velocities remained relatively constant for driving periods exceeding 800 ms. Participants made only gradual changes to their movement parameters, so that they went from a continuous mode to a more discrete mode of behavior for longer driving periods. Thus, unlike for rhythmic bimanual movements or locomotory patterns, there are quantitative but no clear qualitative changes for unimanual movements. The results suggest that participants tried to move close to their preferred tempo at different rates, and that they avoided moving slowly.

Catching Eyes Effects of Social and Nonsocial Cues on Attention Capture

Direct eye contact and motion onset are two powerful cues that capture attention. In the present study, we combined direct gaze with the sudden onset of motion to determine whether these cues have independent or shared influences. Participants identified targets presented randomly on one of four faces. Initially, two faces depicted direct gaze, and two faces depicted averted gaze. Simultaneously with or 900 ms before target presentation, one face with averted gaze switched to direct gaze, and one face with direct gaze switched to averted gaze. When gaze transitions and target presentation were simultaneous, the greatest response-time facilitation occurred at the location of the sudden onset of direct gaze. When target presentation was delayed, direct-gaze cues maintained a facilitatory influence, whereas motion cues induced an inhibitory influence. These findings reveal that gaze cues and motion cues at the same location influence information processing via independent and concurrently acting social and nonsocial attention channels.

The sense of agency during skill learning in individuals and dyads

The sense of agency has received much attention in the context of individual action but not in the context of joint action. We investigated how the sense of agency developed during individual and dyadic performance while people learned a haptic coordination task. The sense of agency increased with better performance in all groups. Individuals and dyads showed a differential sense of agency after initial task learning, with dyads showing a minimal increase. The sense of agency depended on the context in which the task was first learnt, as transfer from joint to individual performance resulted in an illusory boost in the sense of agency. Whereas the quality of performance related to the sense of agency, the generated forces to achieve the task did not. Our findings are consistent with a predictive model account at the perceptual level, such that the sense of agency relies most strongly on sharable perceptual information.

The Posture-Based Motion Planning Framework: New Findings Related to Object Manipulation, Moving Around Obstacles, Moving in Three Spatial Dimensions, and Haptic Tracking

We describe the results of recent studies inspired by the posture-based motion planning theory (Rosenbaum et al., 2001). The research concerns analyses of human object manipulation, obstacle avoidance, three-dimensional movement generation, and haptic tracking, the findings of which are discussed in relation to whether they support or fail to support the premises of the theory. Each of the aforementioned topics potentially challenges the theorys claim that, in motion, goal postures are planned before the selection of movements towards those postures. However, even the quasi-continuous phenomena under study show features that comply with prospective, end-state-based motion planning. We conclude that progress in motor control should not be frustrated by the view that no model is, or will ever be, optimal. Instead, it should find promise in the steady growth of insights afforded by challenges to existing theories.

Coordination of locomotion and prehension

Although locomotion and prehension are commonly coordinated in everyday life, little previous research has focused on this form of coordination. To address this neglected topic, we asked participants to stand a variable distance from a table, walk up to the table, and move an object on the tabletop to a new tabletop position, either to the right or to the left of the object’s initial position and near or far from that initial position. For large manual displacements, which required a step after picking up the object, subjects preferred to stand on the foot opposite the direction of forthcoming manual displacement. By contrast, for small manual displacements, which did not require a step after picking up the object, subjects showed no support-leg preference when they grasped the object prior to manual displacement. The support-leg preferences at grasp time were apparently anticipated by participants as they walked up to the table, indicating considerable long-range planning of entire body positions associated with forthcoming object transfers.

Higher-order action planning for individual and joint object manipulations

Many actions involve multiple action steps, which raises the question how far ahead people plan when they perform such actions. Here, we examined higher-order planning for action sequences and whether people planned similarly or differently when acting individually or together with an action partner. For individual performances, participants picked up an object with one hand and passed it to their other hand before placing it onto a target location. For joint performances, they picked up the object and handed it to their action partner, who placed it onto the target location. Each object could be grasped at only two possible grasping positions, implying that the first selected grasp on the object determined the postures for the rest of the action sequence. By varying the height of the target shelf, we tested whether people planned ahead and modulated their grasp choices to avoid uncomfortable end postures. Our results indicated that participants engaged in higher-order planning, but needed task experience before demonstrating such planning during both individual and joint performances. The rate of learning was similar in the two conditions, and participants transferred experience from individual to joint performance. Our results indicate similarity in mechanisms underlying individual and joint action sequence planning.

Me and we: Metacognition and performance evaluation of joint actions.

Abstract Recent evidence suggests the existence of we-mode processing, but little is still known about how such processing influences the sense of control during intentional joint actions. To examine this issue, dyads performed a video game in which they moved a dot to the target of their choice out of a set of targets. By having each participant control the dot movements in only one dimension (orthogonal to their partner) and by varying the target locations, participants took on different roles. By chance, they also could have congruent or incongruent intentions prior to the movements. In a decider–follower scenario, where one actor decided on the target, judgments of control and judgments of performance depended on whether a prior intention was instantiated, but not on actor role. This finding is consistent with we-mode processing. When participants had conflicting intentions that needed to be resolved online, both the dominant and the nondominant participant showed a marked reduction in the perceived quality of the performance. Thus, dynamic intention negotiation reduced we-mode processing and shifted it toward I-mode processing. The nondominant actor also reported a strongly reduced sense of control. Implications for theories on the sense of agency and for applied settings are discussed.Recent evidence suggests the existence of we-mode processing, but little is still known about how such processing influences the sense of control during intentional joint actions. To examine this issue, dyads performed a video game in which they moved a dot to the target of their choice out of a set of targets. By having each participant control the dot movements in only one dimension (orthogonal to their partner) and by varying the target locations, participants took on different roles. By chance, they also could have congruent or incongruent intentions prior to the movements. In a decider-follower scenario, where one actor decided on the target, judgments of control and judgments of performance depended on whether a prior intention was instantiated, but not on actor role. This finding is consistent with we-mode processing. When participants had conflicting intentions that needed to be resolved online, both the dominant and the nondominant participant showed a marked reduction in the perceived quality of the performance. Thus, dynamic intention negotiation reduced we-mode processing and shifted it toward I-mode processing. The nondominant actor also reported a strongly reduced sense of control. Implications for theories on the sense of agency and for applied settings are discussed.

Entrainment and task co-representation effects for discrete and continuous action sequences

A large body of work has established an influence of other people’s actions on our own actions. For example, actors entrain to the movements of others, in studies that typically employ continuous movements. Likewise, studies on co-representation have shown that people automatically co-represent a co-actor’s task, in studies that typically employ discrete actions. Here we examined entrainment and co-representation within a single task paradigm. Participants sat next to a confederate while simultaneously moving their right hand back and forth between two targets. We crossed whether or not the participant and the confederate moved over an obstacle and manipulated whether participants generated discrete or continuous movement sequences, while varying the space between the actors and whether the actors could see each other’s movements. Participants moved higher when the confederate cleared an obstacle than when he did not. For continuous movements, this effect depended on the availability of visual information, as would be expected on the basis of entrainment. In contrast, the co-actor’s task modulated the height of discrete movements, regardless of the availability of visual information, which is consistent with co-representation. Space did not have an effect. These results provide new insights into the interplay between co-representation and entrainment for discrete- and continuous-action tasks.