The impact of distractions on young adult drivers with attention deficit hyperactivity disorder (ADHD)

Abstract

Young adults with attention deficit hyperactivity disorder (ADHD) are at higher risk for being involved in automobile crashes. Although driving simulators have been used to identify and understand underlying behaviors, prior research has focused largely on single-task, non-distracted driving. However, in-vehicle infotainment and communications systems often vie for a driver's attention, potentially increasing the risk of collision. This paper explores the impact of secondary tasks on individuals with and without ADHD, a medical condition known to affect the regulation of attention. Data are drawn from a validated driving simulation representing periods before, during, and after participation in a secondary cognitive task. A hands-free phone task was employed in a high stimulus, urban setting and a working memory task during low stimulus, highway driving. Drivers with ADHD had more difficulty on the telephone task, yet did not show an increased decrement in driving performance greater than control participants. In contrast, participants with ADHD showed a larger decline in driving performance than controls during a secondary task in a low demand setting. The results suggest that the interaction of the nature of the driving context and the secondary task has a significant influence on how drivers with ADHD allocate attention and, in-turn, on the relative impact on driving performance. Drivers with ADHD appear particularly susceptible to distraction during periods of low stimulus driving.

Introduction

This paper presents the results of a driving simulation study examining the impact of cognitive secondary tasks on young adult drivers with attention deficit hyperactivity disorder (ADHD). Driving simulation has been widely used to assess the performance of drivers with ADHD (Barkley, 2004, Barkley and Cox, 2007, Jerome et al., 2006a, Jerome et al., 2006b). While this work provides useful information on the behavior of drivers with ADHD on and off medication, and in comparison with control samples, to a large extent these studies have not directly examined components of the driving experience that impact inattention, a major impairment in individuals with ADHD. Inattention, or distraction, has long been considered as a factor in automobile crashes (Trott, 1930, as cited in Goodman et al., 1997). Secondary activities are one of the largest contributors to inattentive driving and, subsequently, to accidents (Stutts and Hunter, 2003). Field studies of how in-vehicle distractions affect the allocation of attention in drivers with ADHD are difficult. Driving simulation provides a safe environment and controlled conditions for assessing the ability of this high risk group of drivers to engage in cognitively distracting activities. At the same time, one of the challenges for simulation is the development of scenarios that encourage realistic behavior patterns that are likely to provide insight into behavior relevant to real world driving.

Deviations in an operator's visual attention from the primary driving task to non-driving activities, such as operating the controls of an entertainment system, are relatively easy to identify (Reimer and Sodhi, 2006, Sodhi et al., 2002). During these distracting events, drivers rarely shift their visual attention away from the road for more than 1.6 s (Wierwille et al., 1983). Cognitive distractions are different. With cognitive distractions, an operator's eyes may be directed toward the road but the focus of attention may be elsewhere (Neyens and Boyle, 2007, Reimer, 2009, Smith et al., 2005). The duration of cognitive distractions is often longer, and drivers are sometimes not fully aware of the distraction (Hunton and Rose, 2005, Lesch and Hancock, 2004). Although drivers of all ages fail to divide attention appropriately between driving and secondary tasks, younger drivers are more susceptible to distraction (Klauer et al., 2006, Neyens and Boyle, 2007).

Studies using surveys and official motor vehicle records show that, as a group, individuals with ADHD have poorer driving histories than drivers with other psychiatric disorders (Murphy and Barkley, 1996, Reimer et al., 2005) and display substandard driving habits compared to control subjects (for a complete review of the topic of drivers with ADHD see Barkley, 2004, Barkley and Cox, 2007, Jerome et al., 2006a, Jerome et al., 2006b). The ability to focus attention over extended periods of time and to modulate attention between multiple tasks is impaired in drivers with ADHD (Barkley, 1998). Driving simulation studies show differences in performance between individuals with ADHD and controls or community samples. Additionally, driving simulations have produced evidence supporting the use of medication for improving performance (Barkley, 2004, Barkley and Cox, 2007, Jerome et al., 2006a, Jerome et al., 2006b). Two studies, Laberge et al. (2005) and Reimer et al. (2007), specifically examine the ability of drivers with ADHD to perform under driving conditions associated with inattention in drivers without ADHD. The first of these failed to find a significant impact of secondary task related distractions in participants with ADHD relative to controls. There were, however, significant limitations in the design of the study that may account for this, as will be discussed below. In the second study, during a monotonous portion of a driving simulation designed to enhance the effects of time-on-task fatigue, Reimer et al. (2007) found a higher collision rate for drivers with ADHD as compared to controls.

The objective of the current paper is to explore the impact of cognitive distractions on younger drivers with and without ADHD using data from two segments of a dual task experiment presented sequentially during a validated driving simulation (Reimer et al., 2006). In the first segment, consisting of urban driving, participants were presented with a hands-free phone task (Reimer et al., 2008). Subsequently, a segment of Seidman et al.’s (1998) auditory Continuous Performance Task (CPT), a working memory challenge, was administered while participants navigated a four-lane highway.

The phone task was selected for study based upon its ecological validity, and it was presented in a performance scorable format. Throughout the scenario participants were required to sustain attention to the task while a voice messaging system relayed the more intense cognitive requirements of the conversation. The CPT was selected because of a general documented deficiency in performance on this type of task among individuals with ADHD (Losier et al., 1996), and for the continuous and consistent distraction from the primary demand of driving engendered by this sustained attention task. For purposes of balancing overall task demands in this pilot research, the more difficult CPT was paired with the less taxing highway driving environment.

In this study, we expected that drivers with ADHD would show inferior performance on the secondary tasks, as compared to the control group, because of difficulties associated with sustained attention in ADHD. We predicted that drivers with ADHD would have more difficulty managing the requirements of the simulated driving task for the same reason. Finally, we hypothesized that the driving performance of participants with ADHD would be affected by the dual task to a larger degree than controls.

In a sample of drivers with a higher than average accident risk, the National Highway Transportation Safety Administration's 100 car naturalistic driving study (Klauer et al., 2006) identified driver inattention as a causative factor in 78% of crashes and 65% of near crashes. Younger and less experienced drivers have higher involvement in inattention related crashes. Calculating causation of accidents or near misses, Klauer et al. (2006) was one of the first studies to include driving-related inattention to the forward roadway and non-specific eye glance away from the forward roadway along with the traditional categories of driver distraction (e.g., engagement in a secondary task, driver drowsiness). To enhance internal validity, studies of inattention often investigate each of these classifications separately. Despite the inverse relationship between inattention and safe driving, the degree to which secondary activities in the car distract individual drivers varies greatly. Increased technology in the driver's domain (e.g., cell phones, navigation systems, collision avoidance systems and entertainment systems) makes it increasingly important to understand how attention disorders, such as ADHD, may affect a driver's ability to interact with or resist in-vehicle distraction.

ADHD is known to be a problematic disorder that is generally diagnosed in children. However, ADHD persists into adulthood in a substantial number of cases (Barkley et al., 2002, Faraone et al., 2006) and is increasingly being diagnosed in individuals in their 20s or later (Brown, 2005). It is estimated that at least 4% of adults in the United States are afflicted with ADHD (Kessler et al., 2006). Data from clinical and community samples reveal that ADHD in adults is associated with high levels of morbidity and functional impairment (Biederman, 2004, Wilens et al., 2004). A key area of dysfunction observed with ADHD is impairment in motor vehicle operation. An emerging body of literature shows adverse outcomes among drivers with ADHD. Drivers with ADHD are more likely than drivers without ADHD to commit traffic violations. Adolescents and young adults with ADHD are more likely to be involved and at fault in automobile accidents. For reviews on the topic of drivers with ADHD, refer to Barkley (2004), Barkley and Cox (2007), and Jerome et al., 2006a, Jerome et al., 2006b.

Despite an increased risk of automobile accidents among individuals with ADHD, little research compares the behavior of individuals with and without ADHD to address the issue of causality directly (Reimer et al., 2007). As noted earlier, inattentive driving has a significant influence on automobile accidents. Interactions between driver inattention and medical conditions that impact regulation of attention, however, have yet to be adequately investigated. In a recent review, Barkley and Cox (2007) state that in-vehicle distractions may increase the risk of crashes for individuals with ADHD. While this appears to be a reasonable concern, their review does not cite any studies that provide direct support for this position. There is, however, one study that we are aware of that attempts to address this topic experimentally by measuring the impact of in-vehicle secondary tasks on individuals with ADHD (Laberge et al., 2005).

Laberge et al. (2005) evaluated the driving performance of drivers with ADHD while completing secondary tasks such as adjusting fan settings, changing track numbers on a CD player and participating in a simulated hands-free cell phone conversation. Results of the study failed to confirm the initial hypothesis that “distraction would compound the impairments of ADHD.” Several potential limitations likely contributed to these findings. First, the sample size was small for carrying out an analysis of driving simulation data (seven participants with ADHD and six controls). Second, their use of self-diagnosis of ADHD is not clinically acceptable. Third, the study did not control for ADHD medication status. Finally, the complexity of the in-vehicle tasks employed fell within limits of what drivers are normally expected to be able to handle, thus assessing a relatively low to moderate level of demand on the drivers. This may have limited the sensitivity of the tasks for detecting potentially subtle differences between ADHD and control participants.

This paper expands upon previous research on drivers with ADHD in a manner consistent with of the objectives of Laberge et al. (2005) while addressing the limitations described previously. The current study utilizes a dual task methodology often used in human factors and psychology research for assessing distracted or inattentive driving (Jamson and Merat, 2005, Patten et al., 2004, Reimer et al., 2008). We were also cognizant that in the area of ADHD research, driving simulation studies have frequently used overly complex and low likelihood events (such as obstacles in the road, cars pulling out into traffic, etc.) and high degree of control demands (such as maneuvering between cones and high angle curves) presented at high frequency to potentially enhance differences (Green, 2007). In this study we have employed a scenario designed to limit these events and accidents such that the driving simulation more reasonably reflects the primary task (driving) without influencing the participant with the negative emotional load associated with accidents and frequent unexpected conditions. While this approach may be somewhat less sensitive to possible group differences, it may provide more insight into the potential of adverse driving outcomes under more realistic conditions in cognitively distracted drivers with ADHD.