# Individual Differences in Signal Perception for Takeover Request in Autonomous Driving
## 5 Discussion
In Research Question 3, the objective was to explore the relationship between participants' behavioral responses and their subjective evaluations of signals. Participants were asked to rate which signals they found more noticeable, comfortable, and appropriate to use. The results indicated that the ratings were influenced by the intensity levels of the signal's sub-attributes. The lower the intensity of a signal's sub-attributes, the more negative people rated it. However, for the pitch and loudness of auditory signals and the brightness of visual signals, people preferred the signal with the next-lowest intensity to the highest intensity. If the TOR situation is urgent and life-threatening, the stimulus that will elicit the fastest response should be used, regardless of how people evaluate it [1]. However, in a TOR situation, what is important is not only to alert people but also to achieve accurate situation awareness [40], so a stimulus that is more interactive than one that may cause irritation or narrowing of attention may be appropriate. Subjective ratings also show that older adults are less comfortable with lower pitch stimuli and more comfortable with higher pitch stimuli than other age groups. This is likely related to the cognitive decline that occurs with increasing age [22; 38]. However, older people had similar reaction times to visual signals in this experiment. Although the visual field narrows with age [37], the reaction time to signals is most effective with visual signals in this study. This may be because the design of the study did not allow for other secondary tasks or environmental factors that could have influenced the participants. However, the faster reaction times for visual stimuli compared to other auditory and tactile stimuli suggest that the effectiveness of visual stimuli should be considered when selecting TOR stimuli for older adults. The implication of this study is that the three types of modalities used for TOR were investigated by manipulating the detailed sub-attributes in greater depth. The results of this study, which examined how reaction time changes as the detailed attributes change and whether there is an interaction between the changes in detailed attributes and individual background, can be used as a reference for future TOR signals and are expected to serve as a bridge to further research on individual differences. Despite the valuable insights gained from this study, there are several limitations: Firstly, this study employed arbitrary categories for signal sub-attributes instead of examining them on a continuum. This limited analysis to verifying precise trends in participants' reaction times as the intensity of a specific signal's sub-attributes. Future research could overcome this limitation by implementing a method that allows for a more elaborated exploration of reaction times across a continuum of signal levels. Secondly, the study's examination of personal backgrounds was limited in scope. The duration of the driving simulator experiment and signal evaluation made it hard to add a wider range of driving-related personal backgrounds. Future research should consider incorporating additional personal background variables, such as trust in technology and risk-taking propensity. Additionally, obtaining data on participants' driving behavior directly through the driving simulator could provide further insights into how personal backgrounds relate to driving performance and TOR responses. It is important for future studies to address these limitations to gain a more comprehensive understanding of the relationship between signal, individual differences, and TOR responses in partially autonomous driving situations. By incorporating a continuum of signal levels and considering a broader range of personal backgrounds, researchers can further enhance the validity and applicability of their findings. The findings of the study have direct relevance to the design and implementation of takeover request (TOR) signals in autonomous vehicles.