Aging and working memory modulate the ability to benefit from visible speech and iconic gestures during speech-in-noise comprehension.

When comprehending speech-in-noise (SiN), younger and older adults benefit from seeing the speaker's mouth, i.e. visible speech. Younger adults additionally benefit from manual iconic co-speech gestures. Here, we investigate to what extent younger and older adults benefit from perceiving both visual articulators while comprehending SiN, and whether this is modulated by working memory and inhibitory control. Twenty-eight younger and 28 older adults performed a word recognition task in three visual contexts: mouth blurred (speech-only), visible speech, or visible speech + iconic gesture. The speech signal was either clear or embedded in multitalker babble. Additionally, there were two visual-only conditions (visible speech, visible speech + gesture). Accuracy levels for both age groups were higher when both visual articulators were present compared to either one or none. However, older adults received a significantly smaller benefit than younger adults, although they performed equally well in speech-only and visual-only word recognition. Individual differences in verbal working memory and inhibitory control partly accounted for age-related performance differences. To conclude, perceiving iconic gestures in addition to visible speech improves younger and older adults' comprehension of SiN. Yet, the ability to benefit from this additional visual information is modulated by age and verbal working memory. Future research will have to show whether these findings extend beyond the single word level.

Individual differences in working memory and semantic fluency predict younger and older adults' multimodal recipient design in an interactive spatial task.

Aging appears to impair the ability to adapt speech and gestures based on knowledge shared with an addressee (common ground-based recipient design) in narrative settings. Here, we test whether this extends to spatial settings and is modulated by cognitive abilities. Younger and older adults gave instructions on how to assemble 3D-models from building blocks on six consecutive trials. We induced mutually shared knowledge by either showing speaker and addressee the model beforehand, or not. Additionally, shared knowledge accumulated across the trials. Younger and crucially also older adults provided recipient-designed utterances, indicated by a significant reduction in the number of words and of gestures when common ground was present. Additionally, we observed a reduction in semantic content and a shift in cross-modal distribution of information across trials. Rather than age, individual differences in verbal and visual working memory and semantic fluency predicted the extent of addressee-based adaptations. Thus, in spatial tasks, individual cognitive abilities modulate the interactive language use of both younger and older adults.

Social eye gaze modulates processing of speech and co-speech gesture.

In human face-to-face communication, language comprehension is a multi-modal, situated activity. However, little is known about how we combine information from different modalities during comprehension, and how perceived communicative intentions, often signaled through visual signals, influence this process. We explored this question by simulating a multi-party communication context in which a speaker alternated her gaze between two recipients. Participants viewed speech-only or speech+gesture object-related messages when being addressed (direct gaze) or unaddressed (gaze averted to other participant). They were then asked to choose which of two object images matched the speaker's preceding message. Unaddressed recipients responded significantly more slowly than addressees for speech-only utterances. However, perceiving the same speech accompanied by gestures sped unaddressed recipients up to a level identical to that of addressees. That is, when unaddressed recipients' speech processing suffers, gestures can enhance the comprehension of a speaker's message. We discuss our findings with respect to two hypotheses attempting to account for how social eye gaze may modulate multi-modal language comprehension.