where movements of different geometrical figures (e.g., ovals, squares, triangles) were shown. Importantly, all the videos were silently displayed (i.e., audio removed) and only show the lower part of the actor’s face in order to ensure that his eyes movements could not interfere. Videos were 2 seconds long (Mean: 2000 ms; SD: ssoefiih), they started with 10 frames displaying a closed, still mouth.

2.2. Participants

34 right-handed subjects (12 females) with normal or corrected-to-normal vision and hearing and without any history of psychiatric or neurological disorders will participate in this study. Participant's age range from 25 from 18 to 36 years old (mean XXX, SD XXXX years). The experimental protocol was approved by the Ethics Committee of Pontifical Catholic University of Chile, School of Psychology. Before the experiment started each participant was explained the procedure and signed an informed consent form. Four participants were removed from final analysis because of poor signal-to-noise ratio.

2.3. Procedure

Participants sat at a distance of approximately 70 cm from the computer screen and were asked to attentively observe or imitate the movements displayed in the videos.  The trial started with a word lasting for 500ms that indicate the instruction, either "Observe" or "Imitate". After 100 to 150ms,  a fixation cross appeared for 250ms. In the observation condition, the video was displayed one time, 1000 to 1500ms after the white cross disappeared. In the imitation condition, the video was displayed a first time and participants were asked to attentively observe in order to co-imitate the orofacial gesture when the video was displayed for the second time. The onset of imitation was cued with a red fixation cross. After video offset, a new trial began within 2 to 3 seconds. In order to study the role of automatic mimicry the very same  experiment was repeated in Experiment 2 (B2) where participants were asked to hold an effector depressor horizontally between their teeth (i.e. in the imitation trials, participants were asked to remove the depressor when the word "Imitate" appeared so they can properly imitate). This procedure allowed to imped the automatic mimicry. The order of Experiment 1 and 2 was counterbalanced between participants.
Each of the 5 conditions [i.e., 1) still mouth, 2) syllables, 3)backward played syllables, 4) non-linguistic mouth movements and 5) non-human movements] consist in 3 repetitions of the 24 video-clips, leading to a total of 72 trials per condition (360 per experiment). The experimental design was an intra-subject 5 (type of movements) X 2 (without/with effector restriction) factorial design.

2.4.  Electroencephalographic recording parameters

Electrophysiological activity was register with a 64-channels (Ag-AgCl) EEG system (Biosemi ® ActiveTwo) with electrodes positioned according to the 10-20 international system at a sampling rate of 2048 Hz (band-passed 0.1 to 100Hz). Four external electrodes were used to monitor eye movements. Two of them were placed in the outer canthi of the eyes in order to record horizontal EOG and the other two were positioned above and below the right eye to record vertical EOG. Two additional external electrodes were placed on bilateral mastoids for re-referenciation. 

2.5. Statistical analysis of ERPs

Data pre-processing was performed using MatLab (The Mathworks, Inc.), EEGLAB \cite{Delorme_2004} and ERPLAB toolbox (\cite{Lopez_Calderon_2014}. The signal was first down-sampled at a rate of 512 Hz, band-passed between 0.1 and 40 Hz and re-referenced to mastoides for ERP analysis (primero re-referencia, luego filtro). Then, EEG signal was segmented into epochs from -500ms to 1500ms respective to stimulus onset. Each epoch was visually inspected in order to reject large artifacts due to head movements and muscular artifacts. After Independant Component Analysis (ICA) decomposition , epochs exceeding maximum amplitude of ±100 μV were removed (explica la limpieza por ica, de blinks en particular). The ERP components under interest for statistical analyses were P2, N270, N400 and a positivity around 1000 ms. Using the ERP measurement tool in ERPLAB, mean amplitudes were calculated with respect to a 50 ms prestimulus baseline (un poco chico el baseline, pq tan chico?) for the following selected time windows: P2 [155-185 ms], N270 [245-295 ms], N400 [475-525 ms] and P1000 [975-1025 ms]. After mean amplitudes were extracted for each condition, data were analyzed using a mixed model with experiement (1 or 2) as fixed factor and subjects as aleatory factor.