Title:
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Perception of partners movements in interpersonal coordination :
do human kinematics facilitate rhythmical coordination?
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The synchronisation of interpersonal behaviours in everyday life is essential to achieve
joint actions tasks. Even in social interactions where there is no specific coordination goal,
particular spatio-temporal relations are maintained between individuals unintentionally
and are an important factor in social bonding. Two distinct approaches have been proposed to
understand coordination in interpersonal movements during social interactions: the embodied
simulation approach links behavioural matching to shared neural resources, which are activated
both when an action is observed and when it is performed. Recent studies suggest that only
biological stimuli evoke action imitation, as non-biological stimuli are processed elsewhere in
the brain. An alternative approach, the coordination dynamics perspective, does not specify
any neural substrate but views synchronisation as an emergent phenomenon of an underlying
dynamical process, in which the components of a system self-organise toward a stable state. From
this standpoint, the dynamic patterns of coordination are affected by attributes of the stimulus
kinematics irrespective of whether this stimulus is biological or non-biological in nature.
In this thesis, I investigate whether motion kinematics that are perceived as human will facilitate
interpersonal coordination more readily than stimuli perceived as artificial. First, in
two psychophysical experiments participants were asked to distinguish between real human
movements and artificially produced movements. The findings provide insights into the features
of one-dimensional cyclic movements that allow them to be identified as human; specifically,
observers perceived movements of a particular range of smoothness and frequency as human,
whereas both, very fast or very slow movements outside this range were reliably distinguished
as artificial. Second, these distinct subsets of human and artificial movement kinematics were
applied as stimuli in subsequent intentional and unintentional coordination experiments, and
variations in both the strength and pattern of coordination response was observed. In contrast
to expectations derived from the embodied simulation literature, experiments did not provide
any evidence that the perceptual identification of a stimulus as human matters with regard to
improving coordination. Instead, all modulations in coordination behaviour could be explained
solely on the basis of direct effects of different stimulus kinematics on an underlying dynamical
system. A subsequent modelling study showed that the same patterns of coordination occur with
a system of coupled oscillators when the same stimuli are applied. The consistency between the
theoretical model and empirical results suggests that the observed coordination behaviour in
human subjects can be explained on the basis of an underlying dynamical system, in accordance
with the coordination dynamics approach, without the need to incorporate perceptual factors
or specialised neural networks. Future studies will have to clarify whether factors relating to
the perception of stimuli, predicted by embodied simulation, might become more important in
the absence of larger scale effects associated with stimulus kinematics or with a more ecological
stimulus.
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