Effect of cellular telephone conversations and other potential interference on reaction time in a braking response
Introduction
The widespread use of cellular phones1 by automobile drivers has recently generated safety concerns (Haigney, 1997, Haigney and Westerman, 2001). Particularly influential was a study by Redelmeier and Tibshirani (1997) which found that the use of cellular telephones in automobiles was associated with a quadrupling of collision risk during the brief period of the call. This and other research has suggested that the use of phones while driving can impair aspects of driving performance, possibly increasing accident risk (Alm and Nilsson, 1995, Brookhuis et al., 1991, Brown et al., 1969, McKnight and McKnight, 1993). A debate has ensued concerning the need for legislation restricting the extent to which drivers are permitted to operate a phone in a moving automobile. In the US, efforts to enact laws limiting or prohibiting the use of phones by drivers have increased. One state (New York) and several local municipalities have already restricted the use of phones by drivers.
Most traffic regulations in the US and around the world that apply to cellular phones and driving have focused on the potentially undesirable effects of manipulating a hand-held phone while driving (Lamble et al., 1999), typically by banning the use of hand-held phones, but not hands-free models. Evidently there is a belief that a majority of phone-related accidents occur when a driver is reaching for, dialing, or holding a phone, (it should be noted that unless a hands-free cellular phone uses voice recognition, it too requires manual dialing). Undeniably, manual phone dialing can have a negative effect on driving precision and potentially safety, largely because of the visual demands of manual dialing (Green et al., 1993, Serafin et al., 1993). Relatively long-duration gaze fixations are required to read a phone number and to dial it using a keypad (Reed and Green, 1999). Dialing a phone while driving has been rated as more difficult than most typical driving tasks (Kames, 1978), and data from Japan showed that the majority of cellular phone-related crashes occurred during dialing or receiving calls (National Highway Transportation Safety Administration, 1997).
In contrast, limited US crash data have suggested that a majority of cellular phone-related crashes occur during conversations (National Highway Transportation Safety Administration, 1997). Moreover, Redelmeier and Tibshirani (1997) found no safety advantage to using hands-free compared to hand-held phones, suggesting that accidents result from a driver’s limited attention rather than limited dexterity (like that caused by dialing the phone, holding it, putting it back, etc.). Maclure and Mittleman (1997) contend, however, that Redelmeier and Tibshirani’s study was too small and had too little statistical power to determine whether hands-free phones are safer than hand-held models. Nevertheless, Lamble et al. (1999) provided some support for Redelmeier and Tibshirani’s assertion when they found that drivers’ ability to detect deceleration in a leading car was impaired equally by a ‘non-visual cognitive task’ (meant to simulate a phone conversation) and a keypad dialing task. Apparently, both visual and non-visual cognitive resources are important, such that looking at, manipulating, and using a phone while driving can each affect accident risk (Lamble et al., 1999).
There remain important unanswered questions regarding the effect of phone use on driving performance. It is unclear precisely how the use of phones could contribute to vehicle accidents. The assumption, of course, is that phone use generates interference—but what kind of interference? Tasks can interfere with one another for a variety of reasons, only some of which would be interpretable as interference due to limitations in some central capacity (attention), that is, capacity interference. In contrast, structural interference results when physical structures are the source of the performance decrement (Schmidt and Lee, 1999). A hand can only be one place at a time, and the eyes can be focused only on one signal source at a time. For example, reading a road map while driving could interfere physically with the detection of a road hazard and consequently, delay initiation of an avoidance maneuver. It is possible, even probable, that both capacity interference and structural interference can be generated by cellular phone use while driving.
The critical question is this: how does interference potentially generated by cellular phone use compare to that potentially generated by a variety of common secondary tasks? It is sometimes argued that cellular phones are no worse than other potential distractions drivers encounter routinely, such as conversing with a passenger, eating, drinking, or listing to the radio (Fix, 2001). If this is true, banning the use of phones by drivers while ignoring the risk created by other potential distracters would appear to unreasonably single-out phones for prohibition, especially given the potential benefit of having a phone when traveling by automobile, such as the ability to summon assistance in an emergency. Because little is known about whether phone use is more or less distracting than other secondary tasks, the primary aim of this experiment was to determine the effect of cellular phone conversations and other potential interference on reaction time (RT) in a braking response. RT in a car-following situations is a valid performance parameter, and potentially suitable as part of a driving performance test (Brookhuis et al., 1994).
Section snippets
Participants
Twenty-two (N=22) young adults, 11 women and 11 men, between the ages of 18 and 27 years (mean=21, S.D.=2.1) participated in the experiment. All participants were licensed drivers, and were recruited by word of mouth from among students at Miami University. Seventeen of the 22 participants had used a cellular phone while driving at least once prior to participating in the study.
Apparatus
The apparatus used for the experiment consisted of a laboratory station designed to simulate the foot activity in
Results
The mean RTs for condition A–E are presented in Table 1. The repeated measures ANOVA was significant, F (4,18)=38.51, P<0.0001, and accordingly, pairwise comparisons were performed using Tukey simultaneous tests. The comparisons revealed significant differences between conditions A and C (t=7.84, P<0.0001), D (t=9.28, P<0.0001), and E (t=9.43, P<0.0001). Significant differences were also found between conditions B and C (t=−5.77, P<0.0001), D (t=−7.21, P<0.0001), and E (t=−7.36, P<0.0001).
Cellular phone use and reaction time
This experiment sought to determine the effect of cellular telephone conversations and other potential interference on RT in a braking response. The results supported the first hypothesis—that phone use would cause poorer RT performance in the braking task. The mean difference between condition A (control) and the average of conditions D and E (phone) was +72.5 ms. That is, phone use caused RT to slow by 19%. This finding is consistent with the effect of phone use on RT previously reported by
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