Joint-action coordination in transferring objects

Abstract

Here we report a study of joint-action coordination in transferring objects. Fourteen dyads were asked to repeatedly reposition a cylinder in a shared workspace without using dialogue. Variations in task constraints concerned the size of the two target regions in which the cylinder had to be (re)positioned and the size and weight of the transferred cylinder. Movements of the wrist, index finger and thumb of both actors were recorded by means of a 3D motion-tracking system. Data analyses focused on the interpersonal transfer of lifting-height and movement-speed variations. Whereas the analyses of variance did not reveal any interpersonal transfer effects targeted data comparisons demonstrated that the actor who fetched the cylinder from where the other actor had put it was systematically less surprised by cylinder-weight changes than the actor who was first confronted with such changes. In addition, a moderate, accuracy-constraint independent adaptation to each other's movement speed was found. The current findings suggest that motor resonance plays only a moderate role in collaborative motor control and confirm the independency between sensorimotor and cognitive processing of action-related information.

Fig. 1

Top view of experimental setup depicting the experimental task. The dashed squares represent the starting areas for the (right) hand movements of both actors. At the filled circle a cylinder was positioned which had to be picked up by the putting-actor, repositioned in the central circular target area where the fetching-actor was to pick it up and place it in the target circle in the vicinity of her own starting area

Fig. 2

Kinematics derived from position data of infrared-light emitting diode (IRED) on tip of the thumb, tip of the index finger and wrist as obtained in a prototypical trial. Green (light grey) functions are from the putting-actor, red (dark grey) functions are from the fetching-actor. The top-left graph shows the tangential wrist-velocity time functions, the top-right graph a 3D rendering of finger-thumb displacements, the bottom-left graph shows the aperture-time functions, and the bottom-right graph shows the height (in cm above the table surface) of the midpoint between the thumb and index-finger IREDs

Fig. 3

Means and standard errors of the lifting height (in cm) as a function of role (putting vs. fetching), object diameter (small vs. large) and object weight (light vs. heavy) for repetitions 1, 2 and 3 separately

Fig. 4

Means and standard errors of the lifting height (in cm) of the putting-actor and the fetching-actor. Left-hand graph: whenever the putting-actor showed a lifting-height increase from trial i − 1 to trial i due to an unexpected mass reduction between these trials, the fetching-actor also showed this surprise effect but less strong. Trials i − 1 were the third trials of the trial blocks; trials i were the first trials of the subsequent trial blocks. Right-hand graph: similarly, whenever the putting-actor showed a lifting-height decrease from trial i − 1 to trial i due to an unexpected mass increase between these trials, the fetching-actor also showed this surprise effect, but again, not as strong as the putting-actor did

Fig. 5

Example of the linear regression analysis between the lifting-height data generated by the putter and fetcher of 1 of the 14 dyads participating in the study. The data concern the first trial within trial blocks of three repetitions of the experimental conditions. The regression analyses revealed the robustness of the observed reduction of the size–weight illusion due to movement observation in the dyads studied. The dashed line with slope = 1 represents the situation in which the lifting height of the fetcher would equal that of the putter

Fig. 6

Means and standard errors of the mean wrist speed (in cm/s) as a function of role (putting vs. fetching) and target area size (S = Small, L = Large; p = put, f = fetch). The labels with subscript p reflect the size of the target area of the putting-actor and labels with subscript f reflect the size of the target area of the fetching-actor

Fig. 7

Means and standard errors of the wrist speed (in cm/s) of the putting-actor and the fetching-actor. Left-hand graph: whenever the putting-actor showed a task-unrelated speed increase from trial i − 1 to trial i, the fetching-actor also showed such a speed increase. The trials involved concerned the second and third trials of the trial blocks in which no task conditions changed. Right-hand graph: similarly, whenever the putting-actor showed a task-unrelated speed decrease from trial i − 1 to trial i, the fetching-actor followed this speed decrease

Fig. 8

Example of the linear regression analysis between the wrist-speed data generated by the putter and fetcher of 1 of the 14 dyads participating in the study. The data concern the second and third trials within trial blocks of three repetitions of the experimental conditions. The regression analyzes revealed the robustness of the observed, task-constraint independent covariation of movement speed between the two actors. The dashed line with slope = 1 represents the situation in which the wrist speed of the fetcher would equal that of the putter