Acoustic changes in the production of lexical stress during Lombard speech.

The Lombard effect describes the phenomenon of individuals increasing their vocal intensity when speaking in the presence of background noise. Here, we conducted an investigation of the production of lexical stress during Lombard speech. Participants (N = 27) produced the same sentences in three conditions: one quiet condition and two noise conditions at 70 dB (white noise; multi-talker babble). Manual acoustic analyses (syllable duration, vowel intensity, and vowel fundamental frequency) were completed for repeated productions of two trisyllabic words with opposing patterns of lexical stress (weak-strong; strong-weak) in each of the three conditions. In total, 324 productions were analysed (12 utterances per participant). Results revealed that, rather than increasing vocal intensity equally across syllables, participants alter the degree of stress contrastivity when speaking in noise. This was especially evident in the production of strong-weak lexical stress where there was an increase in contrastivity across syllables in terms of intensity and fundamental frequency. This preliminary study paves the way for further research that is needed to establish these findings using a larger set of multisyllabic stimuli.