Effect of number and placement of EEG electrodes on measurement of neural tracking of speech
Fig 5
Comparison of the channel selection based on the utility metric vs using all the channels (subject-independent scenario).
A Wilcoxon signed rank test showed that there was a significant difference (W = 0, p < 0.001) between the correlation obtained using the optimal number of channels suggested by the utility metric (median = 0.18) compared to the one obtained using all the channels (median = 0.16). (a) Correlation across subjects, computed as the median across folds followed by the median across subjects. Dashed lines show the 25-th (lower) and 75-th (upper) percentile. (b) Standard deviation of the correlation coefficient, computed as the standard deviation across folds followed by the median across subjects. Dashed lines show the 25-th (lower) and 75-th (upper) percentile. (c) Normalized correlation per subject (each line is a different subject), defined as the difference between the value of the correlation obtained when we use all the channels and the value of the correlation obtained when we use a reduced number of channels. (d) Comparison of the correlation obtained using the optimal number of channels (number of channels where each subject obtained the highest correlation) vs the correlation obtained using all the channels. Size of the markers is proportional to the optimal number of channels (one marker per subject). The grey marker has a size equivalent to 64 channels.