Effects on speech intelligibility of temporal jittering and spectral smearing of the high-frequency components of speech

In a previous study, we demonstrated that word recognition performance was reduced when the low-frequency components of speech (0–1.2 kHz) were distorted by temporal jittering, but not when they were distorted by spectral smearing (Pichora-Fuller et al., 2007). Temporal jittering distorts the fine structure of the speech signal with negligible alteration of either its long-term spectral or amplitude envelope characteristics. Spectral smearing simulates the effects of broadened auditory filters that occur with cochlear hearing loss (Baer and Moore, 1993). In the present study, the high-frequency components of speech (1.2–7 kHz) were distorted with jittering and smearing. Word recognition in noise for both distortion conditions was poorer than in the intact condition. However, unlike our previous study, no significant difference was found in word recognition performance in the two distorted conditions. Whereas temporal distortion seems to have a deleterious effect that cannot be attributed to spectral distortion when only the lower frequencies are distorted, when the higher frequencies are distorted both temporal and spectral distortion reduce speech intelligibility.