Modulating Factors of Car Sickness and its Impact on Cognitive and Driving Performance in the Context of Automated Driving

One major benefit of higher levels of automation in cars is the ability to use the regained travel time for other activities, such as working or watching films. However, visual distraction from the driving scene and loss of control over the vehicle can lead to car sickness in susceptible individuals. This not only decreases comfort, but is also likely to negatively affect performance. The latter would not only be undesirable for productivity in non-driving related tasks (NDRTs), but could also impair the ability to safely take vehicle control back and drive manually, which is more critical. This thesis adopts a holistic approach to the issue of car sickness in the context of automated driving (AD), investigating factors preceding and modulating its occurrence, as well as its impact on driving-related cognitive performance and actual takeover and driving performance. To estimate the proportion of people who will be affected by car sickness in AD, Article 1 investigated the current prevalence of car sickness among passengers using an online survey with a large European sample (N = 3.999). Around 30% of participants indicated that they had already experienced car sickness as an adult. The study further addressed the research question of modulating factors of car sickness. It revealed that personal factors (age, gender and driving experience), factors related to living circumstances (e.g., country of residence, how often one is a passenger) and situational factors (the driving situation, seating position, NDRT type) have a significant impact on the occurrence of car sickness. Article 2 further investigated the impact of NDRTs as a modulating factor, paying special attention to the role of the type of visual input. In an open-road study, 20 participants experienced three different NDRTs as front passengers, each with a different visual input: a visual static task (visual n-back), a visual dynamic task (maze game), and an auditory task (auditory n-back), which involved looking down but did not provide additional visual input. The tasks significantly differed in terms of the level of car sickness, with the visual dynamic task leading to the most severe sickness and the auditory task leading to the least. Article 3 addressed the research question regarding the effect of car sickness on cognitive performance relevant to driving. Participants had to perform four different tasks each measuring a specific requirement before (without car sickness) and after the ride (with car sickness). Car sickness did not have an adverse effect on visual performance in visual search tasks. However, reaction times in a simple reaction task increased and hand-eye coordination decreased significantly with increasing car sickness, and there was a tendency for visuo-spatial ability (mental rotation task) to decrease. As these results implied a potential decrease in driving performance, Article 4 followed. The aim of Article 4 was to assess the effect of car sickness on objective takeover and driving performance, and on the subjective experience of it. In a test-track study involving a Wizard-of-Oz vehicle, 33 participants experienced four takeover requests and four subsequent driving tasks (target and emergency braking, slalom with and without speed instruction) both with and without the experience of car sickness. There were no significant differences in objective performance measures for either task. However, participants reported that car sickness significantly decreased their subjective fitness to drive, made driving more demanding and impaired their driving performance. In conclusion, given the anticipated rise in NDRTs during AD, car sickness is expected to be more prevalent among users of automated driving than among conventional car passengers now (30%). However, taking the results of Article 1 into account, this will still not affect the majority of users. Nevertheless, as demonstrated, the occurrence depends heavily on situational factors, making it impossible to provide an exact number. NDRTs proved to play a crucial role in the development of symptoms of car sickness, while visual input that requires constant eye movement appears to be especially provocative. In terms of performance, cognitive impairments due to car sickness were not reflected in impaired driving performance. However, car sickness consistently resulted in a subjective feeling of impairment and exhaustion. Over longer periods of driving, this could lead to fatigue and possibly decreased performance. Based on these results, one could conclude that, objectively, car sickness is not a critical driver state, but, subjectively, it is. This highlights the necessity of including programmes that not only apply countermeasures during automation, but also support a carsick driver during take-over and subsequent manual driving, to avoid rapid exhaustion while driving. Future studies should also investigate more realistic driving scenarios and driving over longer periods to support these findings and assumptions.