Speechreading supplemented with auditorily presented speech parameters.

Results are reported from two experiments in which the benefit of supplementing speechreading with auditorily presented information about the speech signal was investigated. In experiment I, speechreading was supplemented with information about the prosody of the speech signal. For ten normal-hearing subjects with no experience in speechreading, the intelligibility score for sentences increased significantly when speechreading was supplemented with information about the overall amplitude of the speech signal, information about the fundamental frequency, or both. Binary information about voicing appeared not to be a significant supplement. In experiment II, the best-scoring supplements of experiment I were compared with two supplementary signals from our previous studies, i.e., information about the sound-pressure levels in two 1-oct filter bands centered at 500 and 3160 Hz, or information about the frequencies of the first and second formants from voiced speech segments. Sentence-intelligibility scores were measured for 24 normal-hearing subjects with no experience in speechreading, and for 12 normal-hearing experienced speechreaders. For the inexperienced speechreaders, the sound-pressure levels appeared to be the best supplement (87.1% correct syllables). For the experienced speechreaders, the formant-frequency information (88.6% correct), and the fundamental-frequency plus amplitude information (86.0% correct), were equally efficient supplements as the sound-pressure information (86.1% correct). Discrimination of phonemes (both consonants and vowels) was measured for the group of 24 inexperienced speechreaders. Percentage correct responses, confusion among phonemes, and the percentage of transmitted information about different types of manner and place of articulation and about the feature voicing are presented.