[PS-2.24] Drivers - But Not Passengers - Prioritize Driving Over Speech

Kleinman, D. 1 , Ostrand, R. 2 , Ferreira, V. 2 & Bergen, B. 2

1 University of Illinois at Urbana-Champaign
2 University of California, San Diego

Talking while driving dramatically increases the risk of crashing. Clearly, then, holding a conversation requires attentional resources that drivers should - but do not - allocate to driving. What causes this attentional interference?

To address this question, we conducted a driving simulator experiment investigating how drivers and passengers adapt their speech based on the driving environment. Participant pairs (driver + passenger) drove through two courses while one person retold a story to their partner. Driving conditions were difficult (foggy/rainy weather) or easy (clear weather), and the passenger could either see the environment (sighted) or not (blindfolded). Attention to each task was measured by speech rate (talking) and following distance (driving).

Two results indicate that drivers can allocate attention between talking and driving, but that passengers' speech increases driving difficulty. First: Drivers, but not passengers, spoke more slowly during hard driving than easy driving. This difference was attributable to drivers who explicitly mentioned the driving difficulty to their blindfolded passengers (thereby licensing the slowdown). Second: Following distance increased when passengers, but not drivers, spoke faster.

These results suggest that drivers modulate their speech to allocate sufficient attention to driving, but passengers do not take drivers' attentional load into account when speaking.