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Abstract

Coordinating our actions with those of others is a fundamental task in every day life and yet the process of its initiation, development, and termination remains relatively unexplored. While
it is generally agreed upon that humans require a certain period of time to establish a wellfunctioning
joint action behavior, it is an open question whether humans can switch back to
individual behavior instantaneously. In our experiment we investigated the coordination parameters
in the transition from individual behavior to joint action behavior and vice versa.
We employed a large-scale (18x13m), immersive VR environment in which two subjects,
equipped with head-mounted-displays and wireless connected laptops, can be tracked simultaneously
(VICON tracking system) and interact with each other and additional objects. In this
behavioral experiment two subjects were instructed to walkthrough a dynamically generated
maze without colliding with the walls.
In the first condition (Baseline Condition) subjects walked through the maze individually
(20 min). In the second condition (Joint Action Condition) subjects had to transport a stretcher
(length=2.5m) through the maze together (40 min). In the final condition (Follow Condition)
the stretcher was simply removed, and the subject continued walking (10 min) while remaining
a constant distance of 2.5m. Between the first and second condition subjects received a 15
minute break; however between the second and third no pause was made since the immediate
aftereffects of the second condition were to be measured in the third condition. Path characteristics
were specified by a) path length around each corner, b) the minimal distance to the corner,
and c) a symmetry parameter which determines how much a subject’s path deviates from an
ideal, symmetric track.
Compared to the Baseline Condition, participants in the Joint Action Condition increased
as expected their path length and their individual distance to the corner, and deviated from a
symmetric path due to the extended physical boundaries. Furthermore, all three path characteristics
in the Follow Condition showed greater similarities to the Joint Action than to the
Baseline Condition. Even without the necessity for cooperation subjects continued to exhibit a
behavior similar to the Joint Action Condition. This effect can be interpreted as an aftereffect
to the adaptation of the subjects to the joint task, in which compensation was developed gradually.
After prolonged joint action participation, subjects require a particular amount of time or
exercise to return to independent walking behavior.