Interaction between speech variations and background noise on speech intelligibility by Mandarin-speaking cochlear implant patients

Cochlear implant (CI) users have been shown to be more susceptible to the variations in speech production encountered in everyday listening, in which speaking rate, amplitude, duration, and voice pitch information may be quite variable, depending on the production context. Such variations may be further enlarged by the background noise, especially dynamic noise. The limited spectral resolution provided by the CI limits perception of voice pitch, which is an important cue for speech prosody and for tonal languages such as Mandarin Chinese. In this study, the effect of varying speaking rates and styles and background noise on speech understanding was investigated in Mandarin-speaking CI and normal-hearing (NH) listeners. Thirteen (5 male and 8 female, age 19-62 years) Mandarin-speaking, post-lingually deafened adult CI patients using their clinical processors and 9 (5 male and 4 female, age 23-59 years) NH subjects listening to unprocessed speech. Five different types of speech variations, including 3 speaking rates (slow, normal, fast) and 2 speaking styles (emotional, shouted) were presented with two masking noises (speech-shaped steady state noise-SSN or six-talker babble). Speech reception threshold, defined as the signal-to-noise ratio producing 50% correct word-in-sentence recognition using Mandarin Speech Perception materials was measured. NH listeners performed significantly better (16.7 dB) than CI patients across all conditions regardless of speech variations and noise types. CI patients' performance deficit was highly dependent on speech rate and noise type; the deficit was smallest (11.7 dB) when slowly-spoken speech was presented in SSN and largest (20.6 dB) when shouted speech was presented in six-talker speech babble. NH listeners performed significantly better in speech babble than in SSN for all speech variations, while CI patients performed similarly in both noise types. The use of clear and slowly-spoken speech in the laboratory setting may largely underestimate CI patients' performance deficits in real-world listening conditions, where acoustic variations introduced by speech variations and dynamic noise may present additional challenges.