Methodological details.

<p>Procedure (A), examples of lipsmacking, tongue protrusion, and control stimuli (B), and examples of infants' gestures (C). Human models portrayed here have given written informed consent, as outlined in the PLOS consent form, for publication of their photographs.</p

Scatterplots of the relationship between imitation strength and gesture rates during the Return period.

<p>Imitation strength is reported separately for lipsmacking (LPS; plots A and B) and for tongue protrusion (TP; plots C and D), and was calculated using the LPS and TP Imitation Index (see main text). Higher scores indicate stronger imitation. Only for LPS was there a stronger correlation when the return person was the same (A) compared to when the return person was different (B), <i>p</i><.001; for TP there was no difference in the correlation coefficients when the return person was the same (C) or different (D), <i>p</i> = .17.</p

Example of the baseline stimulus (panel A) and the observation trial (panel B).

<p>Example of the baseline stimulus (panel A) and the observation trial (panel B).</p

Mean ERD at C3 and C4 during tool use observation: <i>mu</i> band (panel A), and <i>beta</i> band (panel B).+ <i>p</i> = .05; ** <i>p</i><.01.

<p>Mean ERD at C3 and C4 during tool use observation: <i>mu</i> band (panel A), and <i>beta</i> band (panel B).+ <i>p</i> = .05; ** <i>p</i><.01.</p

Mean ERD by group at frontal, parietal, and occipital sites during tool use observation: <i>alpha</i> band (panel A), and <i>beta</i> band (panel B).

<p>* <i>p</i><.05, ** <i>p</i><.01.</p