Individual Decisions and Perceived Form in Collective Free Improvisation Cl´ ement Canonne 1 & Nicolas Garnier 2 1 Universit´ e de Bourgogne, Centre Georges Chevrier, UMR 7366, 4 boulevard Gabriel, 21072 Dijon CEDEX, France 2 Universit´ e de Lyon, Laboratoire de Physique de l’ENS de Lyon, UMR 5672, 46 all´ ee d’Italie, 69364 Lyon CEDEX 07, France Abstract This paper proposes a first attempt to study quantitatively Collective Free Im- provisation (CFI). We report an experiment designed to study the relationship be- tween the improvisers’ individual high-level decisions and the improvisation’s form perceived by external auditors. We recorded 16 trios in which the improvisers used a MIDI-pedal to indicate in real-time a significant change in their own musical pro- duction. Expert listeners were later asked to segment each improvisation so that we obtained their perception of the structure. By analyzing the correlations between musicians’ individual decisions and listeners’ segmentation points, we discuss how the improvisation’s form emerges from the improvisers’ individual behaviors. While the overall structure depends on individual contributions and decisions which can be well-identified, it is never fully determined by them. Keywords : Improvisation, Interactions, Emergence, Segmentation, Empirical Musi- cology 1