Silent signals: how bodily cues and age influence speech adaptation

Do real-time visual cues of listening effort and expectations on the listener's perceived age drive speech adaptations? In experiment 1, young adults read sentences to a listener shown via a head-mounted display. Participants were told their voices were heard under noisy conditions but received no auditory feedback. The listener, either a young or an old person, was actually a confederate who displayed behaviours indicating easy or hard listening effort pre-recorded using a 360-degree camera. As the listener's visible effort became apparent, speakers increased their vocal intensity and lengthened their utterances. They made larger speech proportion adjustments when addressing the older listener and rated him as understanding less than the younger listener in the easy condition. Experiment 2 found consistent results in older adults. As visible listening effort became evident, older adults increased vocal intensity, extended pauses between words and raised their pitch. They also made stronger speech proportion adjustments when addressing the older listener. Yet, they did not assume the older listener understood less. Thus, although young and older adults differed in their listener's comprehension judgement, both adjusted their speech similarly based on visible effort cues and expectations. These findings reveal Lombard-like speech adaptations driven predominantly by visual cues of listener effort.