Effect of Forward and Backward Coarticulation on the Identification of Speech Sounds

The perceptual effects of forward and backward coarticulation across syllable boundaries were investigated by having 37 female listeners identify: (1) Nasal consonants /m, n, η/ in initial syllables of utterances from which the second syllables were deleted for half of the presentations in noise and (2) Vowels /i, u/ in the deleted syllables when only the initial syllables were presented in quiet. For the deleted condition, post-nasal sounds were erased from the original utterances made up of the initial syllables /t m/, /t n/, /t n/ and second syllables made up only of the vowel /i/ or /u/, or with the intervening consonants /t/ or /st/. Findings included: (1) As the number of consonants separating the nasal consonant and the final vowel increased, there was a significant trend towards fewer correct consonant identifications in the undeleted condition and more correct identifications in the deleted vowel condition, (2) /m/ was identified significantly more often before /u/ than before /i/ while /n/ was identified significantly more often before /i/ than before /u/, (3) No error response pattern was found for the nasal consonant identifications, (4) The undeleted condition produced more correctly identified nasal consonants than the deleted condition, and (5) For the zero intervening-consonant condition, subjects correctly identified deleted second syllable vowels significantly better than chance when only the first syllable was presented. Findings indicate that identification of nasal consonants and vowels is influenced by forward and backward coarticulations but that the co-articulatory effects of bilabiality are only partly perceived.