Unimodal speech perception predicts stable individual differences in audiovisual benefit for phonemes, words and sentences

There are substantial individual differences in the benefit that can be obtained from visual cues during speech perception. Here, 113 normally hearing participants between the ages of 18 and 60 years old completed a three-part experiment investigating the reliability and predictors of individual audiovisual benefit for acoustically degraded speech. Audiovisual benefit was calculated as the relative intelligibility (at the individual-level) of approximately matched (at the group-level) auditory-only and audiovisual speech for materials at three levels of linguistic structure: meaningful sentences, monosyllabic words, and consonants in minimal syllables. This measure of audiovisual benefit was stable across sessions and materials, suggesting that a shared mechanism of audiovisual integration operates across levels of linguistic structure. Information transmission analyses suggested that this may be related to simple phonetic cue extraction: sentence-level audiovisual benefit was reliably predicted by the relative ability to discriminate place of articulation at the consonant-level. Finally, whereas unimodal speech perception was related to cognitive measures (matrix reasoning and vocabulary) and demographics (age and gender), audiovisual benefit was predicted only by unimodal speech perceptual abilities: Better lipreading ability and subclinically poorer hearing (speech reception thresholds) independently predicted enhanced audiovisual benefit. This work has implications for practices in quantifying audiovisual benefit and research identifying strategies to enhance multimodal communication in hearing loss.