Effect of stimulus Category. A. Main effect of stimulus category. Vocoder degraded speech (degraded IS and US) vs. vocoder degraded E (IS+US vs. 2E). The horizontal slice is at the coordinate z = -3 (p < 0.0001). IS-I ntelligible S peech, US-U nintelligible S peech, ES-E nvironmental S ounds. In each group, the darker the color in the bar graphs of BOLD signal variation, the higher the level of vocoder degradation. In blue, areas from TVA localizer are presented at p < 0.05, FWE corrected. B. Degradation effect for speech vs. degradation effect for environmental sounds as defined by the expression (Speechdegraded-Speechnormal)-(Soundsdegraded-Soundsnormal). It can be algebraically rewritten as (Soundsnormal-Soundsdegraded)-(Speechnormal-Speechdegraded). The latter formula makes clear that the difference between normal and degraded stimuli in the right STS is smaller for speech compared with non-speech sounds. In each group, the darker the color in the bar graphs of BOLD signal variation, the higher the level of vocoder degradation.