Figure 2. Inner speech experiment: N1 component analysis.

(A) Waveforms showing the auditory-evoked potentials elicited by the audible phonemes in the Match condition (blue line), Mismatch condition (red line) and Passive condition (black line). The N1-component is labelled; the waveforms were averaged across electrodes FCz, Fz, and Cz, as these were the electrodes at which the N1 component was maximal. The waveforms are shown collapsed across audible phoneme (audible /BA/ and /BI/), and the waveforms for the Match and Mismatch conditions are shown collapsed across inner phoneme (inner /ba/ and /bi/). Voltage maps are plotted separately for each condition; white dots illustrate the electrodes used in the analysis. (B) Box-and-whiskers plots showing the amplitude of the N1 component elicited by the audible phonemes in the Match, Mismatch and Passive conditions. The edges of the boxes represent the top and bottom quartiles, the horizontal stripe represents the median, the cross represents the mean, the whiskers represent the 9th and 91st percentiles, and the colored dots represent the participants whose data fell outside the range defined by the whiskers. (C) Scatterplots showing the within-subjects difference scores (in terms of N1-amplitude) for the three contrasts-of-interest in the inner speech experiment; namely Match minus Mismatch, Match minus Passive, and Mismatch minus Passive. These difference scores were approximately normally distributed with no clear outliers. Each dot represents a single participant’s difference score. The horizontal bars represent the mean, and the error bars represent the 95% confidence interval.