# Individual Differences in Signal Perception for Takeover Request in Autonomous Driving
## 4 Results
### Interaction Effects between Individual Background and Modalities  
To examine the interaction of personal background and modality, a RM ANOVA was conducted for modality and each signal's sub-attributes. The overall mean reaction time per modality was calculated initially, disregarding the sub-attribute of each modality, in order to obtain the mean reaction time for visual, auditory, and tactile cues. Next, the interaction between each individual background and the three modalities on reaction time was analyzed. Age was recoded into three categories: 20-30 s, 40-50 s, and over 60. The interaction between each individual background and the three modalities with respect to reaction times was also examined. The interaction between age and modality was significant, \(F(4,192)=8.82,p<0.001,\eta_{p}{}^{2}=0.16\), with little difference between ages for visual stimuli but significant increases in reaction time with age for auditory and tactile stimuli (Figure 3a). All other interactions effects between individual background and modality were not significant. Next, the interaction effects between the level of each modality sub-attribute and personal background were analyzed. Similar to previous analysis, significant interactions were observed between age and amplitude for tactile cues, \(F(6,282)=4.94\), \(p<0.001\), \(\eta_{p}{}^{2}=0.10\); loudness for auditory cues, \(F(6,282)=10.70\), \(p<0.001\), \(\eta_{p}{}^{2}=0.19\); and pitch for auditory cues, \(F(6,282)=4.63\), \(p<0.001\), \(\eta_{p}{}^{2}=0.09\). Specifically, the age differences were most prominent at the lowest levels of tactile amplitude and auditory loudness and pitch (Figure 3b-d). There were no differences based on other individual backgrounds. To investigate how participants' reaction times changed as the strength of each signal's sub-attributes varied, main effects of sub-attributes were analyzed. These analyses aimed to identify any trend lines or patterns in participants' reaction times corresponding to changes  
Figure 3: Interaction effect of the experiment: (**a**) interaction effect between age and modality; (**b**) interaction effect between auditory loudness and age; (**c**) interaction effect between auditory pitch and age; (**d**) interaction effect between tactile amplitude and age. in the strength of the sub-attributes within each signal. For all sub-attributes, the main effect of sub-attributes level was significant at the 0.05 level of significance. To determine whether this main effect was due to the lowest level of each stimulus sub-attribute, the lowest level was excluded, and a RM ANOVA was conducted on the remaining three levels and found that there was still a significant difference at the 0.05 level of significance. The result indicated that TOR reaction time decreased as each modality's sub-attribute level increased (e.g., tactile amplitude increased, auditory pitch increased, visual size increased; Figure 4a-c). To further examine the main effects identified in this study, post hoc tests using the Bonferroni method ware conducted. These tests enabled pairwise comparisons between different levels of the signal sub-attributes within each main effect, providing insights into specific differences in participants' reaction times. The post hoc tests using the Bonferroni method revealed significant differences between all conditions (lowest to highest intensity) for both frequency in tactile signals and loudness in auditory signals. These differences were significant at the 0.001 level of significance. This indicates that participants' reaction times showed continuous changes as the signal became louder or the vibration frequency increased. There was no significant difference in the amplitude of the tactile signal between 8 v and 12 v or pitch of the auditory signal between 1000 Hz and 2000 Hz. For visual signals, no significant differences were observed except for the comparison between the lowest intensity and other levels.