Listener Discrimination and Effort in Different Levels of Background Noise for Clear Speech Produced by Speakers With Parkinson Disease.

Purpose: The purpose of this study was to determine the effect of clear speech on listener discrimination and listener effort.

Method: Seventeen normal-hearing young adults listened to recorded sentences spoken by individuals with Parkinson disease and hypokinetic dysarthria pre- and post-clear speech instruction. Sentences were presented in the background noise at four different signal-to-noise ratios (SNRs). We quantified listener discrimination by the number of correct words the participant repeated back and the SNR at which the participant achieved 50% correct word recognition (SNR-50). We quantified listener effort subjectively and with pupillometry. Mixed-model analyses of variance were used to determine the main effect of speech condition (habitual, clear), the main effect of dB SNR (+10, +5, 0, and -5), and the interaction between speech condition and dB SNR for (a) number of correct words, (b) subjective listening effort, and (c) mean pupil diameter. A paired-samples t test was used to determine the difference in SNR-50 between habitual and clear speech conditions.

Results: Better discrimination in the clear condition was indicated by significantly more correct words repeated back and a significantly lower SNR-50. Reduced listening effort in the clear condition was indicated by significantly lower subjectively reported listening effort and smaller mean pupil diameter. The greatest difference between the clear and habitual condition was at 0 dB SNR.

Conclusions: Clear speech instruction improved listener discrimination and reduced effort indicated by subjective, behavioral, and physiological measurements. The greatest improvement was seen in adverse listening conditions with background noise, but when the background noise was too loud to overcome, there was no benefit to hearing clear versus habitual speech.