Figure 3.

Speech realignment. (A) Overt speech analysis—the overall reconstruction accuracy for the overt speech condition was quantified by computing directly the correlation coefficient (Pearson's r) between the reconstructed and original speech representations (B) Covert speech analysis—the covert speech reconstruction is not necessarily aligned to the corresponding overt speech representation due to speaking rate differences and repetition irregularities. The reconstruction was thus realigned to the overt speech stimuli using dynamic time warping. The overall reconstruction accuracy was then quantified by computing the correlation coefficient (Pearson's r) between the covert speech reconstruction and the original speech representation. (C) Baseline control analysis—a resting state (baseline control) condition was used to assess statistical significance of covert speech reconstruction accuracy. Resting state activity was used to generate a noise reconstruction and dynamic time warping was applied to align the noise reconstruction to overt speech as in (B). Because dynamic time warping has substantial degrees of freedom, due to its ability to stretch and compress speech segments, the overall reconstruction accuracy for the baseline control condition is significantly higher than zero. However, direct statistical comparisons between the covert and baseline conditions are valid as equivalent analysis procedures are applied to both covert and resting state neural data.