Cell-Phone–Induced Driver Distraction

Our research examined the effects of handsfree cell-phone conversations on simulated driving. We found that even when participants looked directly at objects in the driving environment, they were less likely to create a durable memory of those objects if they were conversing on a cell phone. This pattern was obtained for objects of both high and low relevance, suggesting that very little semantic analysis of the objects occurs outside the restricted focus of attention. Moreover, in-vehicle conversations do not interfere with driving as much as cell-phone conversations do, because drivers are better able to synchronize the processing demands of driving with invehicle conversations than with cell-phone conversations. Together, these data support an inattention-blindness interpretation wherein the disruptive effects of cell-phone conversations on driving are due in large part to the diversion of attention from driving to the phone conversation. KEYWORDS—driver distraction; inattention blindness; attention; cell phones This article focuses on a dual-task activity that over 100 million drivers in the United States currently engage in: the concurrent use of a cell phone while operating a motor vehicle. It is now well established that cell-phone use significantly impairs driving performance (e.g., McEvoy et al., 2005; Redelmeier & Tibshirani, 1997; Strayer, Drews, & Johnston, 2003; Strayer & Johnston, 2001). For example, our earlier research found that cell-phone conversations made drivers more likely to miss traffic signals and react more slowly to the signals that they did detect (Strayer & Johnston, 2001). Moreover, equivalent deficits in driving performance were obtained for users of both hand-held and hands-free cell phones (see also Strayer, Drews, & Crouch, 2006). By contrast, listening to radio broadcasts or books on tape did not impair driving. These findings are important because they demonstrate that listening to verbal material, by itself, is not sufficient to produce the dual-task interference associated with using a cell phone while driving. The data indicate that when a driver becomes involved in a cell-phone conversation, attention is withdrawn from the processing of the information in the driving environment necessary for safe operation of the motor vehicle. EVIDENCE OF INATTENTION BLINDNESS The objective of this article is to muster evidence in support of the hypothesis that cell-phone conversations impair driving by inducing a form of inattention blindness in which drivers fail to see objects in their driving environment when they are talking on a cell phone. Our first study examined how cell-phone conversations affect drivers’ attention to objects they encounter while driving. We contrasted performance when participants were driving but not conversing (i.e., single-task conditions) with that when participants were driving and conversing on a hands-free cell phone (i.e., dual-task conditions). We used an incidentalrecognition-memory paradigm to assess what information in the driving scene participants attended to while driving. The procedure required participants to perform a simulated driving task without the foreknowledge that their memory for objects in the driving scene would be subsequently tested. Later, participants were given a surprise recognition-memory test in which they were shown objects that had been presented while they were driving and were asked to discriminate these objects from foils that had not been in the driving scene. Differences in incidental recognition memory between singleand dual-task conditions provide an estimate of the degree to which attention to visual information in the driving environment is distracted by cellphone conversations. Each of the four studies we report here used a computerized driving simulator (made by I-SIM; shown in Fig. 1) with high-resolution displays providing a 180-degree field of view. (The dashboard instrumentation, steering wheel, gas, and brake pedal are from a Ford Crown Victoria sedan with an automatic transmission.) The simulator incorporates vehicle-dynamics, Address correspondence to David Strayer, Department of Psychology, 380 S. 1530 E. RM 502, University of Utah, Salt Lake City, UT 84112; e-mail: [email protected]. CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE 128 Volume 16—Number 3 Copyright r 2007 Association for Psychological Science traffic-scenario, and road-surface software to provide realistic scenes and traffic conditions. We monitored the eye fixations of participants using a video-based eye-tracker (Applied Science Laboratories Model 501) that allows a free range of head and eye movements, thereby affording naturalistic viewing conditions for participants as they negotiated the driving environment. The dual-task conditions in our studies involved naturalistic conversations with a confederate on a cell phone. To avoid any possible interference from manual components of cell-phone use, participants used a hands-free cell phone that was positioned and adjusted before driving began (see Fig. 1). Additionally, the call was begun before participants began the dual-task scenarios. Thus, any dual-task interference that we observed had to be due to the cell-phone conversation itself, as there was no manual manipulation of the cell phone during the dual-task portions of the study. Our first study focused on the conditional probability of participants recognizing objects that they had fixated on while driving. This analysis specifically tested for memory of objects presented where a given driver’s eyes had been directed. The conditional probability analysis revealed that participants were more than twice as likely to recognize roadway signs encountered in the single-task condition than in the dual-task condition. That is, when we focused our analysis on objects in the driving scene on which participants had fixated, we found significant differences in recognition memory between singleand dual-task conditions. Moreover, our analysis found that even when participants’ eyes were directed at objects in the driving environment for the same duration, they were less likely to remember them if they were conversing on a cellular phone. The data are consistent with the inattention-blindness hypothesis: The cell-phone conversation disrupts performance by diverting attention from the external environment associated with the driving task to an engaging context associated with the cellphone conversation. Our second study examined the extent to which drivers who engage in cell-phone conversations strategically reallocate attention from the processing of less-relevant information in the driving scene to the cell-phone conversation while continuing to give highest priority to the processing of task-relevant information in the driving scene. If such a reallocation policy were observed, it would suggest that drivers might be able to learn how to safely use cell phones while driving. The procedure was similar to that of the first study except that we used a two-alternative forced-choice recognition-memory paradigm to determine what information in the driving scene participants attended to while driving. We placed 30 objects varying in relevance to safe driving (e.g., pedestrians, cars, trucks, signs, billboards, etc.) along the roadway in the driving scene; another 30 objects were not presented in the driving scene and served as foils in the recognition-memory task. There were different driving scenarios for different participants and target objects for some participants were foil objects for others. Objects in the driving scene were positioned so that they were clearly in view as participants drove past them, and the target and foils were counterbalanced across participants. Here again, participants were not informed about the memory test until after they had completed the driving portions of the study. As in the first study, we computed the conditional probability of recognizing an object given that participants fixated on it while driving. Like the first study, this analysis specifically tested for memory of objects that were located where the driver’s eyes had been directed. We found that participants were more likely to recognize objects encountered in the single-task condition than in the dual-task condition and that this difference was not affected by how long they had fixated on the objects. Thus, when we ensured that participants looked at an object for the same amount of time, we found significant differences in recognition memory between singleand dual-task conditions. After each forced-choice judgment, participants were also asked to rate the objects in terms of their relevance to safe driving, using a 10-point scale (participants were initially given an example in which a child playing near the road might receive a rating of 9 or 10, whereas a sign documenting that a volunteer group cleans a particular section of the highway might receive a rating of 1). Participants’ safety-relevance ratings ranged from 1.5 to 8, with an average of 4.1. A series of regression analyses revealed that there was no association between recognition memory and traffic relevance. In fact, traffic relevance had absolutely no effect on the difference in recognition memory between singleand dual-task conditions, suggesting that the contribution of an object’s perceived relevance to recognitionmemory performance is negligible. This analysis is important because it indicates that drivers do not strategically reallocate attention from the processing of less-relevant information in the driving scene to the cell-phone conversation while continuing to give highest priority to the processing of task-relevant information in the driving scene. Fig. 1. A participant talking on a hands-free cell phone while driving in the simulator. Volume 16—Number 3 129 David L. Strayer and Frank A. Drews