Individuality and togetherness in joint improvised motion

Abstract

Actors, dancers and musicians that improvise together report special moments of togetherness: high performance and synchrony, seemingly without a leader and a follower. Togetherness seems to conflict with individuality- the idiosyncratic character of each person's performance. To understand the relation of individuality and togetherness, we employed the mirror game paradigm in which two players are asked to mirror each other and create interesting synchronized motion, with and without a designated leader. The mirror game enables quantitative characterization of moments of togetherness in which complex motion is generated with high synchrony. We find that each person as a leader does basic strokes of motion with a characteristic signature, in terms of the shape of their velocity profile between two stopping events. In moments of togetherness both players change their signature to a universal stroke shape. This universal velocity profile resembles a half-period of a sine wave, and is therefore symmetric and maximally smooth. Thus, instead of converging to an intermediate motion signature, or having one player dominate, players seem to shift their basic motion signatures to a shape that is altogether different from their individually preferred shapes; the resulting motion may be easier to predict and to agree on. The players then build complex motion by using such smooth elementary strokes.

Figure 1. Joint improvised motion in the mirror game was analyzed in terms of elementary motion events called segments.

(A) In the one dimensional mirror game players move handles along parallel tracks, and motion is tracked. Lights indicate type of round: red leads, blue leads or no designated leader. (B) Examples of velocity traces from two different games. Red trace marks the red player and blue trace marks the blue player. All traces are taken from rounds with no designated leader. Notice the high synchronization of the motion in both cases and its relative complexity. (C) A motion segment is defined as the velocity trace between two consecutive zero velocity points. The shape of segment velocity traces is characterized by two parameters: skewness – the shift to the left or right, and kurtosis – the relative weight on the curve ‘shoulders’. Throughout the paper each segment is described as a point in this two-dimensional low-level motion parameter plane. The segment characteristics of each player are described by an ellipse whose center is the mean and its axes are the standard deviation (error bars) of the skewness and kurtosis values.

Figure 2. Players show individual signature in the shapes of their segment velocity traces.

(A) The motion of each player while playing as a leader is represented by an ellipse, which represents one standard deviation around the mean of all segments by that player in one game (between 47 to 392 segments/game, median = 170 segments/game). Insets are examples of velocity segments. (B) The distribution of different players' mean kurtosis and skewness values as leaders (blue), and of two expert players who played multiple games (16 and 8 games, red and orange curves).

Figure 3. In co-confident motion, all players show a universal shape in their segments.

(A) Examples of two games in which players have individual segment characteristics when they lead (blue and red ellipses), and show a distinct segment shape in CC motion (full green ellipses). (B) Despite the variability in player signatures as leaders (blue ellipses), all players converge on a similar region of segment shape space during CC motion (green ellipses). (C) The distribution of players' mean kurtosis and skewness values as leaders (blue) and in CC motion (green). Also shown are the leader characteristics of the two expert players who played multiple games (repeating players, red and orange).

Figure 4. The universal co-confident segments are symmetric and smooth.

Co-confident segments (green ellipses) cluster around kurtosis and skewness values similar to the minimal jerk solution for periodic motion (the trace which minimizes the integral over the acceleration change squared, resembles a half-sine wave). The characteristic of the half-sine wave lie in the center of the co-confident region in segment shape space. For comparison, a Gaussian trace, with kurtosis computed as 3, is shown far from the observed motion. Insets: pure Gaussian and half-sine traces and two examples of traces from the dataset.

Figure 5. Players meet at a universal region of motion space when in togetherness, instead of meeting at their mean motion.

Schematics of three possible hypotheses: (A) Hypothesis One: One player mimics the other players' segment signature during co-confident motion. (B) Hypothesis Two: Both players tune their signatures and meet, during co-confident motion, at an intermediate position in segment shape space. Meeting region is different for each game and depends on both players' signatures. (C) Hypothesis Three: All players tune their signatures to meet at a universal region of the segment shape space. Co-confident motion region is common to all games. This describes the present findings.