The order of the two autonomous simulations were randomized. Following each use of the driving simulator, participants completed a Simulator Sickness Ques-.
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Electrodermal Response and Automation Trust during Simulated Self-Driving Car Use Drew M. Morris, Jason M. Erno, & June J. Pilcher Department of Psychology; Clemson University, Clemson, SC The integration of self-driving vehicles may expose individuals with health concerns to undue amounts of stress. Psychophysiological indicators of stress were used to determine changes in tonic and phasic stress levels brought about by a high-fidelity autonomous vehicle simulation. Twenty-eight participants completed one manual driving task and two automated driving tasks. Participants reported their subjective level of trust in the automated systems using the Automation Trust Survey. Psychophysiological stress was indexed using skin conductance and trapezius muscle tension. Results indicate that users show more signs of physiological stress when the vehicle drives autonomously than when the users is in control. Results also indicate that users show an additional increase in stress when the user reports low trust in the autonomous vehicle. These findings suggest that health-care professionals and manufactures should be aware of additional stress associated with self-driving technology.
Copyright 2017 by Human Factors and Ergonomics Society. DOI 10.1177/1541931213601921
INTRODUCTION Self-driving vehicles are currently entering the user market, both as personal vehicles and autonomous taxi services. Although the level of automation varies by manufacturer and model, many proposed models are fully autonomous and strictly limit user input (Schoettle & Sivak, 2014). Although non-autonomous vehicles will still have a presence on the road, it will become increasingly likely that users who are uncomfortable with having limited control will need to rely on them in some capacity. Because of this potential schism, using self-driving vehicles may place an undue amount of stress on users who are not comfortable with these systems (Banks, Stanton, & Harvey, 2014). One reason for this discomfort could be user distrust of automation competency. Factors such as perceived mindfulness and anthropomorphic features seem to moderate the trustworthiness of autonomous vehicles, and indeed influence willingness to use advanced technology (Waytz, Heafner, & Epley, 2014). As a result, public surveys have shown that the general population is concerned about the use of autonomous vehicles. This is largely due to feelings that vehicles cannot perform as well as humans, and a general lack of understanding regarding automation decision making (Koo et al.,
2015; Schoettle & Sivak, 2014). Consequently, it seems likely that using autonomous vehicles would act as a stressor to those who do not trust the technology (Reimer, Mehler, & Coughlin, 2016). Humans encounter psychological and physiological stress on a daily basis. Whether it is running from a threat, standing at a cold bus stop, or mitigating social dilemmas, humans use physiological and psychological mechanisms to manage stress levels in an attempt to perform optimally (Lazarus, 1990). However, for some populations, this increased stress can be a health risk (Cooper & Marshall, 2013). Indeed, stress itself is a risk factor for those with arrhythmia or hypertension, as well as those with anxiety disorders. Despite our knowledge of stress as a health risk factor, little is known about stress during autonomous vehicle use. In particular, previous literature has not shown whether early users of autonomous technology show signs of increased stress during use, a question of importance to the healthcare community. Research has demonstrated that some specific activities associated with driving automation (e.g., crashing or self-parking) can increase heart rate, but this tells us little about normal autonomous vehicle use (Waytz et al., 2014; Wintersberger & Riener, 2016). Understanding this question could shape the way physicians supervise
Proceedings of the Human Factors and Ergonomics Society 2017 Annual Meeting
their patients at risk for stress related health problems – those with vulnerable postoperative periods or generalized anxiety, for instance. In these cases, use of autonomous self-driving technology may pose a significant risk that health practitioners should be aware of. One method of objectively measuring stress is by recording psychophysiological measures of the sympathetic branch of the autonomic nervous system. Common indices of the psychophysiological stress include measures of skin conductance via eccrine gland activation (Storm et al., 2002) and muscle tension from the trapezius muscles (Lundberg et al., 1994). These methods have been shown to be non-invasive and reliable measures of psychological and physical stress. Purpose and Hypotheses The goal of the current study is to explore whether using a simulated autonomous vehicle could bring about a significant physiological stress response. In addition, the study also explores whether vehicle behavior influences automation trust and user stress. 1) The researchers hypothesize that users will show an increased physiological stress response when the vehicle is in a self-driving mode than when the user is in control. 2) The researchers also hypothesize that users will demonstrate a larger physiological stress response when the vehicle behaves in a way that is perceived at distrustful. METHOD Participants Twenty-eight healthy young adults (22 females, 19.43±1.23 years) participated in a series of driving tasks during a single testing session. Participants were screened for normal driving behavior using the Driving Habits Questionnaire (Owsley, Stalvey, Wells, & Sloane, 1999). Participants reported driving an average of 4±2.5 times per week and all considered themselves average to good drivers. This study was approved by the institutional review board and all participants provided consent prior to participation.
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Materials and Tasks Physiological indices of stress were measured continuously using a ProComp Infiniti multichannel data logger (Thought Technology; Montréal, Canada). Measures included phalangeal skin conductance (SC), and trapezius muscle tension measured through surface electromyography (EMG). Driving and simulated autonomous driving were performed in a high fidelity driving simulator (DriveSafety Inc.; Murray, UT). The simulator used a fully functioning vehicle cab on a pitch and longitudinal mobile base with and a 300◦ projection environment. Two different tracks were used during the study. Track one was a highway road with a 55mph speed limit, no traffic, and two gradual turns. Track one was used to allow participants to feel comfortable with the simulator and was also used during the manual driving task. Track two was also a highway road with a 55mph speed limit, but with light traffic and one blind turn. Track two was used during the two autonomous vehicle scenarios. In one scenario of the autonomous vehicle, the vehicle was programed to obey all the rules of the road (Safe), while in the other scenario, the vehicle was programed to speed and drift within its lane (Risky). The order of the two autonomous simulations were randomized. Following each use of the driving simulator, participants completed a Simulator Sickness Questionnaire to control for feelings of illness (Kennedy, Lane, Berbaum, & Lilienthal, 1993). Participants who reported feelings of simulator sickness were immediately excused from the study. Following each use of an autonomous vehicle scenario, participants completed the 12-item Automation Trust Survey (Jian, Bisantz, & Drury, 2000). Values for this scale range from 1 (do not trust at all) to 5 (extremely trustworthy). Procedure Participants arrived at the lab and completed a short general information and demographics questionnaire, followed by the Driving Habits Questionnaire. Next, participants had the physiological sensors attached, and sat quietly in the driver’s seat of the simulator for five minutes to record a physiolog-
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ical resting baseline. After the resting baseline, participants drove Track one for ten minutes, the last five minutes of which were recorded as the manual driving task/driving baseline. After driving themselves, participants were put into one of the two simulated autonomous scenarios (Safe or Risky). After the first scenario, the participants completed the Automation Trust Survey then started the second scenario. The participants then completed a second Automation Trust Survey for that scenario and the session was concluded. RESULTS The results of a paired samples t-test showed that, based on the Automation Trust Survey, participants trusted the autonomous vehicle less while it demonstrated risky behavior (1.94±0.85) compared to safe behavior (3.63±0.58), t(28)=10.49, p.05); however, participants showed significantly higher skin conductance while being driven in the safe driving autonomous mode (4.21±3.47) than when users drove themselves (3.51±2.90), t(27)=3.85, p=0.001, d=1.48. Additionally, participants showed significantly higher skin conductance when being driven in the risky autonomous driving scenario (4.53±3.53) than in the safe autonomous driving scenario (4.21±3.47), t(27)=4.38, p
