Effects of spectral alternation upon intelligibility of words and sentences

Abstract

In the study of a novel speech interference paradigm, it was found that periodic alternation between nonoverlapping filtering conditions—1100 Hz low pass and 1700 Hz high pass—significantly reduced intelligibility. Thus, although repetition accuracy for CID sentences was approximately 98% in either the low‐pass or high‐pass filtering condition alone, subjects averaged only 48% correct when sentences were subjected to spectral alternation at a rate of 2.67 Hz. Interestingly, the intelligibility of spectrally alternated sentences was dramatically improved by the addition of appropriately filtered noise bands. Thus, when low‐pass noise was mixed with segments of high‐pass speech, and high‐pass noise was mixed with segments of low‐pass speech, repetition accuracy increased by 38.8%. A smaller but statistically significant increase was also found for isolated words. The intelligibility loss produced by spectral alternation appears related to other verbal and musical phenomena. The results from various control conditions indicate that the enhancement of intelligibility produced by alternating noise bands involved separate phonemic restorations for each band. [Work supported by NIH and NSF.]