Effects of cognitive load on response time in an unexpected lead vehicle braking scenario and the detection response task (DRT)

Journal article, 2018

The effects of cognitive distraction on traffic safety and driver performance are unclear and under debate. Based on increased response times to stimuli or events in controlled driving experiments, concerns, primarily about cell phone usage during driving, have been raised. But while cognitive load repeatedly have been shown to increase response times in artificial tasks such as the Detection Response Task (DRT), the generalizability of the results to response times in critical traffic situations is questionable. Method: Two experiments were conducted. In Experiment 1, response times in the DRT were measured during simulated driving with and without execution of a cognitively loading secondary task. In Experiment 2, brake response times in an unexpected lead vehicle braking scenario were measured with and without the same cognitively loading task. Results: In Experiment 1, DRT response times increased with increased level of cognitive load. In Experiment 2, brake response times were unaffected by cognitive load. Conclusion: The response time results from the artificial DRT did not generalize to the critical lead vehicle braking scenario. This finding can possibly be explained by the cognitive control hypothesis, which suggests that cognitive load selectively impairs driving subtasks that rely on cognitive control (i.e. novel or inconsistent tasks) but leaves automatic performance unaffected (Engström, Markkula, Victor, & Merat, 2017). While the DRT responses, because of the task novelty, can be assumed to require cognitive control, responses to visually expanding objects, such as a braking lead vehicle with short time headway, are triggered automatically. Common interpretations of the effect of cognitive load on traffic safety thus need to be re-examined. It seems inappropriate to generalize from effects of cognitive load on DRT, or other artificial laboratory tasks that rely on cognitive control, to unexpected real-world situations where responses are triggered primarily by looming cues.