Revealing action representation processes in audio perception using fractal EEG analysis.

Electroencephalogram (EEG) recordings, and especially the Mu-rhythm over the sensorimotor cortex that relates to the activation of the mirror neuron system (MNS), were acquired from two subject groups (orchestral musicians and nonmusicians), in order to explore action representation processes involved in the perception and performance of musical pieces. Two types of stimuli were used, i.e., an auditory one consisting of an excerpt of Beethoven's fifth symphony and a visual one presenting a conductor directing an orchestra performing the same excerpt of the piece. Three tasks were conducted including auditory stimulation, audiovisual stimulation, and visual stimulation only, and the acquired signals were processed using fractal [time-dependent fractal dimension (FD) estimation] and statistical analysis (analysis of variance, Mann-Whitney). Experimental results showed significant differences between the two groups while desychronization of the Mu-rhythm, which can be linked to MNS activation, was observed during all tasks for the musicians' group, as opposed to the nonmusicians' group who exhibited similar response only when the visual stimulus was present. The mobility of the conductor was also correlated to the estimated FD signals, showing significantly higher correlation for the case of musicians compared to nonmusicians' one. The present study sheds light upon the difference in action representation in auditory perception between musicians and nonmusicians and paves the way for better comprehension of the underlying mechanisms of the MNS.