The use of mobile phones has been shown to increase drivers' reaction times (RTs), but whether this results from interference with attention, stimulus identification, or response production remains unclear. We recorded RTs and event-related brain potentials (ERPs) reflecting speed of stimulus processing, attentional allocation, and preparedness to respond during a visual reaction task performed with or without the concomitant use of a mobile phone, in either "hands-free" or "phone-in-hand" operating modes. As expected, maintaining a phone conversation increased RTs to visual targets, this effect being associated with complex ERP effects. Phone conversations did not appear to delay target detection times, as assessed by N2-P3 latencies, but did significantly decrease stimulus-induced alerting and attentional allocation (P3 amplitude) and interfered with motor preparation processes (readiness potential). P3 amplitude drop was identical whatever the mode of phone use, while decrease of readiness potential was progressive from the "hands-free" to the "phone-in-hand" condition. These results suggest that two mechanisms contributed to degrade performance in this experiment: first, a general decrease of attention to sensory inputs, characteristic of "dual-task" situations, probably acting through a delay in sensory-motor transfer times. This effect was independent of whether the phone was handled or "hands-free." Conversely, the second factor was specifically sensitive to manipulation of the phone and caused a weakening of the readiness to respond with a motor act. (A)
Abstract