# Individual Differences in Signal Perception for Takeover Request in Autonomous Driving
## 2 Related Works
### Takeover Request and Modality  
In the context of manual driving, warning signals indicate the likelihood of a collision with another object, taking lateral and longitudinal coordinates into account. The specifics of the signals can substantially affect the reaction time of the driver. In a study conducted by [PERSON] et al., the researchers manipulated factors such as signal loudness for auditory signals, signal amplitude for tactile signals, and signal size and luminance for visual signals in order to determine their effect on participants' reaction times [20]. The study found a correlation between the frequency of tactile signals and the pitch of auditory signals and quicker reaction times [20]. Using this line of inquiry as a basis, [PERSON] et al. implemented a driving scenario involving participants and manipulated the warning signal characteristics to observe their responses [21]. Their findings have been extensively cited as a standard in subsequent research. Consequently, the majority of research on signaling for takeover requests in the context of partially autonomous driving has focused on comparing various modalities using predefined stimuli or investigating the effects of multimodality. Research on the modality of the takeover request (TOR) can be broadly divided into three categories. First, research has investigated the effect of distinct modalities on human perception in TOR situations [25]. For example, professional drivers have shown that a combination of forward collision and lane change warnings is appropriate for commercial motor vehicles. However, they exhibited typically negative responses to the use of haptic presentation modalities for warnings [26]. The second area of study investigates individual differences in objective or subjective responses to TOR signaling. This can be accomplished via surveys and experiments. Younger adults responded to auditory and tactile stimuli in TOR situations faster than older adults, according to one study [27]. In some instances, however, older drivers demonstrated response times comparable to those of younger drivers [28]. In addition, research indicates that older drivers tend to focus more on the road and less on secondary tasks [29]. The third area of study focuses on cross-modality comparisons. Similar to the cross-modality comparisons conducted in manual driving [7; 30], a number of studies [5; 14; 31; 32] have investigated which modality is more effective at triggering driver responses during control transitions in partial autonomy. However, these studies occasionally produce contradictory results. Depending on variables such as secondary tasks or timing, some studies have found that tactile cues are more effective than auditory cues [31; 32], while others have found the opposite [5; 14]. Each study's stimuli were generated by manipulating a number of variables, including pitch and loudness for auditory stimuli, amplitude and cycle for tactile stimuli, and luminance and size for visual stimuli. Such data are summarized in Table 1. An important question arises: Are differences in driver responses to stimuli across different modalities primarily influenced by the cognitive characteristics of individuals or by differences in stimulus characteristics? In the investigations of [PERSON] et al. and [PERSON] et al., tactile cues were more effective than auditory cues [7; 31]. However, according to studies of [PERSON] et al. and [PERSON] et al., auditory cues are superior to tactile cues [5; 14]. Is this difference owing to the experiment's context or purpose? Or, is it possible to achieve various outcomes by altering the stimuli within the same context? It is possible that a small modification, such as increasing the auditory stimulus loudness by 10 dB, could eliminate the observed difference. Therefore, it is essential to precisely define the detailed characteristics of the stimuli used in the experiment and compare the effectiveness of each modality.