Effects of intermodal timing difference and speed difference on auditory‐visual speech perception

Previous studies have shown that lipreaders possess insufficient sensitivity to intermodal timing differences and adapt to the timing difference when it is kept constant. This study investigated effects of intermodal timing differences and speed differences on auditory‐visual speech perception. We used 20 minimal pairs of Japanese four‐mora words such as mizuage (catch landing) versus mizuame (starch syrup). We administered intelligibility tests to younger and older adults. Words were presented under visual‐only, auditory‐only, and auditory‐visual (AV) conditions. Effects of AV asynchrony by time‐expanded speech (speed difference) on AV benefit (i.e., the superiority of AV performance over auditory‐only performance) were compared with those by intermodal timing shift (timing difference). Results showed that the AV benefit declined as the timing difference and speed difference increased. Results also revealed that younger adults adapted to the timing difference but did not adapt to the speed difference. Ol...