Fig. 1.

Experimental methods. A: first formant frequency (F1) of the target vowel sound (red) in “HEAD” was shifted downwards (white) in real time. B: representative data of F1 over all trials. As feedback is perturbed (green), subjects alter their production (black) relative to baseline (red). When feedback returns to normal after training, subject shows after-effect (blue). C: group average of F1 among subjects who successfully learned the task. The three phases, baseline, early training and late training, are shown in gray boxes. Subjects compensated for the downward shift in their formant frequency. D: scalp topography of the electrodes that were used for recording event-related potentials (ERPs) are shown in gray. The electrodes that showed significant changes in phase coherence are labeled and marked in black. E: example ERPs over electrode Cz at different experimental phases (baseline: red; early training: black; late training: blue). The ERPs are aligned at the voice onset and show changing activity during planning and production of speech utterance. The thickness of the lines indicate SE of the mean.