Physical characteristics of the lips underlying vowel lipreading performance

To evaluate the relationship between physical characteristics of the lips during vowel production and vowel lipreading confusions, four female talkers were videotaped producing 15 American English vowels and diphthongs in an /h/-V-/g/ context. Ten normal-hearing adults identified the stimuli through lipreading. Three analyses were performed. First, using confusion matrices for individual and pooled talkers, the stimuli were located in a two-dimensional space using multidimensional scaling. The ten monophthongs revealed a clear lip spreading/rounding dimension and a tongue height dimension, and while diphthongs also showed influence of lip rounding, more variability on the tongue height dimension was apparent. Second, tracings were made of the talkers' lips on a single videotape field representing the maximum opening or constriction for each of the 40 monophthong tokens (ten vowels X four talkers), and six physical measurements of the tokens were derived as descriptors of the vowel nuclei. Third, difference scores and other measures of physical pairwise similarity were used as predictors of two ways of representing the vowel lipreading confusions in a multiple regression paradigm. Results indicated that the physical measures were moderately successful as predictors of vowel perception (accounting for approximately 50% of the variance in the perceptual distance measure), although considerable differences in the strength of the prediction occurred among talkers.