  Extensive experiments in Human Movement Science suggest that solo motions are
characterized by unique features that define the individuality or motor
signature of people. While interacting with others, humans tend to
spontaneously coordinate their movement and unconsciously give rise to joint
improvisation. However, it has yet to be shed light on the relationship between
individuality and joint improvisation. By means of an ad-hoc virtual agent, in
this work we uncover the internal mechanisms of the transition from solo to
joint improvised motion in the mirror game, a simple yet effective paradigm for
studying interpersonal human coordination. According to the analysis of
experimental data, normalized segments of velocity in solo motion are regarded
as individual motor signature, and the existence of velocity segments
possessing a prescribed signature is theoretically guaranteed. In this work, we
first develop a systematic approach based on velocity segments to generate
\emph{in-silico} trajectories of a given human participant playing solo. Then
we present an online algorithm for the virtual player to produce joint
improvised motion with another agent while exhibiting some desired kinematic
characteristics, and to account for movement coordination and mutual adaptation
during joint action tasks. Finally, we demonstrate that the proposed approach
succeeds in revealing the kinematic features transition from solo to joint
improvised motions, thus revealing the existence of a tight relationship
between individuality and joint improvisation.
