Speech produced in noise (or Lombard speech) is characterized by increased vocal effort, but also by amplified lip gestures. The current study examines whether this enhancement of visible speech cues may be sought by the speaker, even unconsciously, in order to improve his visual intelligibility. One subject played an interactive game in a quiet situation and then in 85dB of cocktail-party noise, for three conditions of interaction: without interaction, in face-to-face interaction, and in a situation of audio interaction only. The audio signal was recorded simultaneously with articulatory movements, using 3D electromagnetic articulography. The results showed that acoustic modifications of speech in noise were greater when the interlocutor could not see the speaker. Furthermore, tongue movements that are hardly visible were not particularly amplified in noise. Lip movements that are very visible were not more enhanced in noise when the interlocutors could see each other. Actually, they were more enhanced in the situation of audio interaction only. These results support the idea that this speaker did not make use of the visual channel to improve his intelligibility, and that his hyperarticulation was just an indirect correlate of increased vocal effort.

Index Terms: Lombard speech, hyper-articulation, audiovisual intelligibility, multimodality