The dual-task costs of audiovisual benefit: Effects of noise and "native" speaker status.

Listeners typically understand speech more accurately when they can see and hear the talker relative to hearing alone. However, seeing the talker's face does not necessarily reduce the cognitive costs associated with processing speech as measured by dual-task costs. In difficult listening conditions, dual-task response times may be faster for audiovisual than audio-only speech, but when listening conditions are easy, the presence of a talking face may have no effect on dual task responses or even slow responses relative to listening alone. The current study expanded upon this work by including samples of both native and nonnative English speakers and assessing speech intelligibility, subjective listening effort (Experiment 1), and dual-task costs (Experiment 2) for audio-only and audiovisual speech across multiple noise levels. We found that seeing the talker reduces dual-task costs only in difficult listening conditions in which the visual information is necessary to accurately identify the speech. The effects of background noise and speech modality were robust within groups of native as well as nonnative listeners, suggesting that if researchers are interested in studying general phenomena related to speech processing (i.e., rather than specifically studying how language background affects results), these effects would have emerged regardless of whether the sample was limited to native speakers of English. However, the magnitude of some effects differed for native and nonnative listeners.