Summary of the MNE results. Left: Regions of interest (ROIs) in the left and right hemisphere modulated by the acoustic quality of speech, the intelligibility of speech, and the attentive state of the listener during the N1m, P2m, Early SF and Late SF time ranges. Right: MNE source currents within the affected ROIs during each time range. During the N1m time range, sensitivity to acoustic structure was evident in the central superior temporal (CST) and central inferior parietal (CIP) areas where stimulus degradation increased cortical activation. During the P2m time range, areas surrounding the CST in the superior and inferior temporal areas were more active during intelligible speech, regardless of whether the speech was acoustically distorted or not. In the early SF time range, the central temporal areas (CST & CIT) exhibited stronger activity to acoustically degraded speech while the posterior superior temporal (PST) area was sensitive to the intelligibility of speech. During the late SF, an attention-related effect was observable in the parietal brain areas (CSP). Error bars indicate the standard error of the mean (SEM).