Effects of Phonetic Context on Audio-Visual Intelligibility of French

Bimodal perception leads to better speech understanding than auditory perception alone. We evaluated the overall benefit of lip-reading on natural utterances of French produced by a single speaker. Eighteen French subjects with good audition and vision were administered a closed set identification test of VCVCV nonsense words consisting of three vowels i, a, y and six consonants b, v, z, 3, R, l. Stimuli were presented under both auditory and audio-visual conditions with white noise added at various signal-to-noise ratios. Identification scores were higher in the bimodal condition than in the auditory-alone condition, especially in situations where acoustic information was reduced. The auditory and audio-visual intelligibility of the three vowels i, a, y averaged over the six consonantal contexts was evaluated as well. Two different hierarchies of intelligibility were found. Auditorily, a was most intelligible, followed by i and then by y; whereas visually y was most intelligible, followed by a and i. We also quantified the contextual effects of the three vowels on the auditory and audio-visual intelligibility of the consonants. Both the auditory and the audio-visual intelligibility of surrounding consonants was highest in the a context, followed by the i context and lastly the y context.