# Impact of Dual-Depth Head-Up Displays on Vehicle Driver Performance
## 2 Materials and Methods
### Apparatus  
**Microsoft HoloLens2:**  
In this study, Microsoft HoloLens2 (Microsoft, Redmond, WA, USA) headset augmented reality glasses were used as a display tool for head-up displays with the following specifications: resolution: 2k 3:2 light engines, holographic density: > 2.5 k radiants (light points per radian), the maximum brightness of 500-600 nit, FOV 43\({}^{\circ}\)\(\times\) 29\({}^{\circ}\) (diagonal 52\({}^{\circ}\)), and IR camera that can track the position of human eyes to display images.  
**EEG:**  
In this study, the BIOPAC MP150 System (Biopac, Goleta, CA, USA) and EEG100C signal amplifier (Biopac) were used to record the EEG of the subjects during the whole driving process. The EEG electrode positions of the 10-20 system were adopted, and the measuring electrode points were F3, F4, P3, P4, O1, and O2. The brainwave energy of each electrode was calculated to evaluate the change in brainwave energy of the subjects at different periods.  
**EOG:**  
In this study, BIOPAC MP150 System combined with the EOG100C signal amplifier was used to record the electro-ophthalmogram of subjects driving throughout the whole process and calculate the change in blink frequency of subjects (times/min). According to [PERSON] et al., when people are visually fatigued, blink frequency will increase significantly [27]. Therefore, this study evaluated the changes in visual fatigue of subjects at different periods by measuring blink rate.  
**NASA-TLX:**  
[PERSON] and [PERSON] et al. proposed a set of questionnaires for multi-dimensional workload assessment in 1988 [28]. NASA-TLX workload questionnaire defined six dimensions, including mental load, physiological load, time load, performance, effort level, and frustration level. In this study, the NASA-TLX questionnaire was used for subjective assessment of driving workload. The questionnaire was filled out after the experiment, and the score of the questionnaire was used as the basis of workload. The higher the score,  
Figure 1: Single Depth.  
Figure 2: Dual Depth.  
the higher the subjective feeling of workload; the lower the score, the lower the subjective feeling of workload.  
**Experimental environment (experimental space and driving simulator):**  
To ensure the consistency of the viewing quality of the subjects, the test site was set in a dark room that was not interfered with by external light; there were no other noisy sounds around, and the indoor temperature was controlled at 24 \(\pm\) 1 \({}^{\circ}\)C. To increase the sense of driving reality, the body size of the BMW 728 was used as the specification of the driving simulator, as shown in Figure 3. The projection screen is projected 2.5 m in front of the seat, the width of the projection screen is 2.6 m, the width of the vehicle is 1.8 m, and the height of the seat is 0.6 m from the ground, as shown in Figure 4.  
We used Unity 2020.3.25f1 and the plugins Fantastic City, EasyRoads3D Pro v3 for scene construction, and NWH Vehicle Physics 2 for vehicle physics engine as the simulated driving environment in this article. In this paper, two scenes were constructed, namely, an urban scene (Figure 5) and a straight monotonous road (Figure 6). The urban scene included buildings, traffic signals, trees, etc., and we drove about 10 min to reach the data recording starting point according to navigation instructions and speed limits. The urban scene was not included in the data analysis for familiarizing participants with the operation of equipment.  
Figure 4: Driving simulator specifications.  
Figure 5: Experimental scenes (urban).  
Figure 3: Real car specifications.