The Modulation Transfer Function for Speech Intelligibility
Figure 3
Comprehension of low-pass modulation filtered sentences.
(A,B) Grayed areas of thumbnails show spectrotemporal modulations removed by low-pass modulation filtering in the spectral (A) or temporal (B) domain. Units and axis ranges are the same as in Figure 2. Each thumbnail represents a stimulus set analyzed in (C,D). (C,D) Mean±s.e. performance in transcribing words from the low-pass modulation filtered sentences. Cutoff frequencies on the x-axes of the two graphs are presented in units appropriate to the spectral or temporal domain, but could equally well be viewed on one continuous scale in either unit. Symbols show SNR levels. Dashed line shows control performance at +2 dB SNR; dotted line shows control performance at −3 dB SNR. Points at cutoff frequencies which share no capital letters in common (above line plots) are significantly different (repeated measures ANOVA, Bonferroni post-hoc correction, p<0.0008) at the +2 dB SNR condition. (E and G) Spectrograms of an example sentence (same as in Figure 1) with the most extreme spectral modulation filtering (with a low-pass cutoff of 0.5 cycles/kHz; Audio S2) and the spectral modulation filtering at which comprehension became significantly worse (4 cycles/kHz; Audio S3), respectively. LP = Low-pass. (F and H) Spectrograms of the example sentence with the most extreme temporal modulation filtering tested (having a low-pass cutoff of ∼3 Hz; Audio S4), and the temporal modulation filtering at which comprehension became significantly worse (cutoff 12 Hz; Audio S5).