Correlation between age and intelligibility index (i.e., difference in tracking of natural and reversed speech) and comparison of age groups. (A) Statistical values of the voxel-wise correlation of the formant–brain intelligibility index with age (averaged over 1–7 Hz, P <0.05, cluster corrected) showing a strong decrease of intelligibility tracking in occipital regions and in cingulate cortex. (B) Correlation of formant–brain intelligibility index in significant occipital voxels extracted from a showing a significant correlation with age (P = 5.14e−07). (C) Correlation of lip–brain intelligibility index in significant occipital voxels extracted from a showing a not-significant correlation with age (P = 0.726). (D) Correlation of formant–brain intelligibility index in significant voxels from the cingulate cortex extracted from a showing a significant correlation with age (P = 4.99e−06). (E) Correlation of lip–brain intelligibility index in significant voxels from the cingulate cortex extracted from a showing a not-significant correlation with age (P = 0.368). Blue lines depict regression lines, and shaded areas depict SE.