Fig. 6: Shared representations between internal speech, vocalized speech and written word processing.
From: Representation of internal speech by single neurons in human supramarginal gyrus
a, Evaluating the overlap of shared information between different task phases in the ‘auditory cue’ task. For each of the ten session days, cross-phase classification was performed. It consisted in training a model on a subset of data from one phase (for example, cue) and applying it on a subset of data from ITI, cue, internal and speech phases. This analysis was performed separately for each task phase. PCA was performed on the training data, an LDA model was constructed and classification accuracies were plotted with a 95% confidence interval over session means. Significant differences in performance between phases were evaluated between the ten sessions (paired two-tailed t-test, FDR corrected, d.f. 9, P < 0.001 for all, Cohen’s d ≥ 1.89). For easier visibility, significant differences between ITI and other phases were not plotted. b, Same as a for the ‘written cue’ task (paired two-tailed t-test, FDR corrected, d.f. 9, PCue_Internal = 0.028, Cohen’s d > 0.86; PCue_Speech = 0.022, Cohen’s d = 0.95; all others P < 0.001 and Cohen’s d ≥ 1.65). c, The percentage of neurons tuned during the internal speech phase that are also tuned during the vocalized speech phase. Neurons tuned during the internal speech phase were computed as in Fig. 3b separately for each session day. From these, the percentage of neurons that were also tuned during vocalized speech was calculated. More than 80% of neurons during internal speech were also tuned during vocalized speech (82% in the ‘auditory cue’ task, 85% in the ‘written cue’ task). In total, 71% of ‘auditory cue’ and 79% ‘written cue’ neurons also preserved tuning to at least one identical word during internal speech and vocalized speech phases. d, The percentage of neurons tuned during the internal speech phase that were also tuned during the cue phase. Right: 78% of neurons tuned during internal speech were also tuned during the written cue phase. Left: a smaller 47% of neurons tuned during the internal speech phase were also tuned during the auditory cue phase. In total, 71% of neurons preserved tuning between the written cue phase and the internal speech phase, while 42% of neurons preserved tuning between the auditory cue and the internal speech phase.
