Effects of listening demand on turn-taking processes: Investigating turn-end prediction and verbal response planning

During conversation, speakers often take turns with little gap or overlap. But older adults with hearing loss are often slower to take turns and show more variability in turn timing than older adults with normal hearing, potentially due to increased cognitive demands of processing speech with hearing loss. In this study, we investigated how hearing loss and listening demand affect turn-end prediction and verbal response planning - two processes thought to support timely turn-taking. We developed a single task that captured these two processes, instructing participants to listen to semantically predictable and unpredictable turns and press a button when they thought the turn would end before producing a verbal response. Experiment 1 validated this task, demonstrating that younger adults with normal hearing responded faster when turns were predictable rather than unpredictable. Experiment 2 investigated how listening demand and hearing loss affected these processes by comparing older adults with normal hearing (PwNH) listening at low demand (a highly intelligible level of 70 dB) to older adults with hearing loss (PwHL) listening at either low demand (i.e., 70 dB), or high demand (the lowest level above 60 dB at which the participant could report >70 % of words). Participants again responded faster for predictable than unpredictable turns. Additionally, PwHL in the low demand group showed larger predictability effects than PwNH. In contrast, PwHL in the high demand group showed no difference to PwNH in turn-end prediction but a delay in verbal response production. Together, these findings suggest that content predictability facilitates both turn-end prediction and response planning in such a 'listen-to-respond' task, and that adults with hearing loss show particular reliance on prediction when listening demand is low, which may buffer against turn-taking delays.