Examining whether mental resource or response competition causes spatial cell phone conversations to impair driving

Cellular phone conversations clearly impair driving performance (Gugerty, Rakouskas, & Brooks, 2004; Kass, Cole, & Stanny, 2007; McKnight & McKnight, 1993; Strayer, Drews, & Johnston, 2003; Strayer & Johnston, 2001). Two independent experiments were developed to compare the response and resource competition explanations of dual-task impairments observed during concurrent cell phone conversations and driving. The former suggests that people cannot drive and talk on their cell phone because both of these tasks require response selection. The latter suggests that drivers cannot drive and talk on their cell phone because these two tasks compete for the same mental resources. The purpose of the first experiment was to determine if a specific spatial task utilized spatial resources. Indeed, performance on a validated tracking task was slower and less accurate during a dual-task condition in which participants shadowed spatial route descriptions compared to a single-task tracking condition. The purpose of the second experiment was to determine whether a response or resource competition was responsible for degraded performance during simulated driving. The results indicated that participants’ average braking response times were slower, their average headway was greater, their average speed was higher, and they were involved in more collisions with a lead vehicle compared to a single-task driving condition. This means that a spatial shadowing task, that did not require response selection, interfered with driving performance. Further, the results also demonstrated that participants’ average braking response times were slower, their headway and lane position varied more, their average speed was higher, and they were involved in more collisions during a spatial inquiry phase, that did require response selection, compared to the spatial shadowing phase. Collectively, these results mean that both explanations are at work. Resource and response competition both have the potential to impair driving performance.