Intelligibility of bandpass-filtered speech

Warren et al. [Percept. Psychophys. 57, 175–182 (1995)] reported high intelligibility for sentences processed by one-third octave bandpass filters. The present study examined the contribution of acoustic and linguistic redundancy to the intelligibility of filtered speech. Separate groups of listeners identified sentences or isolated final words from the SPIN (‘‘speech perception in noise’’) test. One group heard unfiltered speech, while others heard filtered speech with center frequencies of 750, 1100, 1500, 2100, or 3000 Hz. Gammatone filters with bandwidths of 1 ERB were used to match auditory filter widths. Consistent with Warren et al., the 1500-, 2100-, and 3000-Hz bands were more intelligible than the lower bands. Filtered words in high-predictability (HP) sentences were identified more accurately than those in low-predictability (LP) sentences (mean difference 20%). Isolated filtered words were less intelligible than LP sentences (23% difference). Unfiltered HP and LP sentences and final words were equally intelligible, with scores exceeding 94%. Filtered HP sentences were well identified for the 2100- and 3000-Hz bands, with performance similar to unfiltered sentences. These findings support the hypothesis that context is emphasized when the acoustic signal is degraded, and illustrate the interactive nature of multilevel processing.