Visual vowel and diphthong perception from two horizontal viewing angles.
This study investigated vowel and diphthong lipreading performance from 0 degree and 90 degree angles of observation. Sixteen English vowels and diphthongs were placed in an /h-g/ context to form the stimulus items. Each item was presented by a speaker ten times in random order for a total of 160 items. The speaker was simultaneously videotaped from 0 degree and 90 degree angles under optimal lighting conditions. Ten normal hearing adults subjects phonetically recorded the vowel or diphtong they perceived as each item was visually presented. The diphthong stimuli were significantly easier to identify than the vowel stimuli at both angles of observation. In addition, no significant differences were found between the 0 degree and 90 degree angles in terms of percentage of correct identifications of all phonemes examined. Orderly, predictable confusions also were observed. Those confusions occurring in visual diphthong recognition tended to shift toward the stressed vowel element of the diphthong or to a vowel produced in a manner similar to the stressed element.