Does it help to see the speaker’s lip movements?

Simultaneous interpreting combines auditory and visual information. Within a multitude of visual inputs that interpreters receive, the one from the speaker seems to be particularly important (Bühler 1985; Seubert 2019). One reason might be that lip movements enhance speech perception and might thus reduce cognitive load in simultaneous interpreting and hence, induce lower mental effort. This effect may be even more pronounced when noise is added to the source speech. This study was conducted to investigate cognitive load and mental effort during simultaneous interpreting (a) with and without the ability to see speaker’s lip movements, and (b) with and without interfering noise. A group of listeners was included to control for task-related effects. Mental effort and cognitive load were measured using pupillometry, interpreting accuracy measures, and subjective reports. The facilitation hypothesis for lip movements was not confirmed. However, the pupillometric data suggests that lip movements may increase arousal.