The impact of age and mutually shared knowledge on multi-modal utterance design

Previous work suggests that the communicative behavior of older adults differs systematically from that of younger adults. For instance, older adults produce significantly fewer representational gestures than younger adults in monologue description tasks (Cohen & Borsoi, 1996; Feyereisen & Havard, 1999). In addition, older adults seem to have more difficulty than younger adults in establishing common ground (i.e. knowledge, assumptions, and beliefs mutually shared between a speaker and an addressee, Clark, 1996) in speech in a referential communication paradigm (Horton & Spieler, 2007). Here we investigated whether older adults take such common ground into account when designing multi-modal utterances for an addressee. The present experiment com- pared the speech and co-speech gesture production of two age groups (young: 20-30 years, old: 65-75 years) in an inter- active setting, manipulating the amount of common ground between participants. Thirty-two pairs of nave participants (16 young, 16 old, same-age-pairs only) took part in the experiment. One of the participants (the speaker) narrated short cartoon stories to the other participant (the addressee) (task 1) and gave instruc- tions on how to assemble a 3D model from wooden building blocks (task 2). In both tasks, we varied the amount of infor- mation mutually shared between the two participants (com- mon ground manipulation). Additionally, we also obtained a range of cognitive measures from the speaker: verbal work- ing memory (operation span task), visual working memory (visual patterns test and Corsi block test), processing speed and executive functioning (trail making test parts A + B) and a semantic fluency measure (animal naming task). Prelimi- nary data analysis of about half the final sample suggests that overall, speakers use fewer words per narration/instruction when there is shared knowledge with the addressee, in line with previous findings (e.g. Clark & Wilkes-Gibbs, 1986). This effect is larger for young than for old adults, potentially indicating that older adults have more difficulties taking com- mon ground into account when formulating utterances. Fur- ther, representational co-speech gestures were produced at the same rate by both age groups regardless of common ground condition in the narration task (in line with Campisi & zyrek, 2013). In the building block task, however, the trend for the young adults is to gesture at a higher rate in the common ground condition, suggesting that they rely more on the vi- sual modality here (cf. Holler & Wilkin, 2009). The same trend could not be found for the old adults. Within the next three months, we will extend our analysis a) by taking a wider range of gesture types (interactive gestures, beats) into ac- count and b) by looking at qualitative features of speech (in- formation content) and co-speech gestures (size, shape, tim- ing). Finally, we will correlate the resulting data with the data from the cognitive tests. This study will contribute to a better understanding of the communicative strategies of a growing aging population as well as to the body of research on co-speech gesture use in addressee design. It also addresses the relationship between cognitive abilities on the one hand and co-speech gesture production on the other hand, potentially informing existing models of co-speech gesture production