An analysis of the effects of clear speech on the visual-speech intelligibility of consonants

Gagné and Rochette [1] reported that the use of clear speech improved the overall visual-speech intelligibility of consonants. The data from that investigation were re-analyzed to examine the effects of clear speech on six individual consonants (/b,v,d,z,Ζ,g/) presented in three different symmetrical v-C-v contexts (/a,i,y/). The stimuli were spoken by six female talkers who produced four iterations of the stimulus set in two different speaking styles: conversational and clear speech. The results were based on the responses obtained from 13 adult subjects. Only the data from the visual-speech recognition task were considered. The results showed significant main effects of consonant and vowel context, as well as a significant interaction between consonant and vowel context. Overall, the findings suggest that the visual-speech intelligibility of consonants is strongly influenced by the vowel context in which they are spoken. In general, greater clear speech benefits were observed for consonants with a place of articulation located at the back of the oral cavity (i.e., post-alveolars and velars) than those with a place of articulation that is more centrally located in the oral cavity (i.e., labiodentals and alveolars). The effect of clear speech on the visual-speech intelligibility of bilabials was negligible.