Speaking in the presence of noise: Consistency of acoustic properties in clear-Lombard speech over time.

Individual speakers are often able to modify their speech to facilitate communication in challenging conditions, such as speaking in a noisy environment. Such vocal "enrichments" might include reductions in speech rate or increases in acoustic contrasts. However, it is unclear how consistently speakers enrich their speech over time. This study examined inter-speaker variability in the speech enrichment modifications applied by speakers. The study compared a baseline habitual speaking style to a clear-Lombard style and measured changes in acoustic differences between the two styles over sentence trials. Seventy-eight young adult participants read out sentences in the habitual and clear-Lombard speaking styles. Acoustic differences between speaking styles generally increased nonlinearly over trials, suggesting that speakers require practice before realizing their full speech enrichment potential when speaking clearly in noise with reduced auditory feedback. Using a recent objective intelligibility metric based on glimpses, the study also found that predicted intelligibility increased over trials, highlighting that communicative benefits of the clear-Lombard style are not static. These findings underline the dynamic nature of speaking styles.