The Modulation Transfer Function for Speech Intelligibility
Figure 4
Comprehension of speech with notch-filtered modulations or “core” modulations.
(A–C) The speech modulation spectrum with filtered modulations denoted by grayed areas as in Figure 5A. (A) Spectral notch modulation filters. (B) Temporal notch modulation filters. (C) Core modulations most essential to comprehension in Figure 5 are depicted in full and zoomed-in thumbnail plots. Stimuli for the core condition were obtained by low-pass filtering in both the spectral and temporal modulation domains. (D,E) Mean±s.e. comprehension when either spectral (D) or temporal (E) modulation filters were applied to the sentences, along with control sentences (lighter gray bars) containing all or only core modulations (C). Stimulus conditions which share no lower case letters (above plots) in common are significantly different, as in Figure 5 (repeated measures ANOVA). (F) Spectrogram of the example sentence after spectral modulations between 3 and 7 cycles/kHz were filtered out (Audio S6). (G) Spectrogram of the example sentence containing only the core of essential modulations below 7.75 Hz and 3.75 cycles/kHz (Audio S7).