Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The title and objectives stated in the abstract of the paper correspond to its content.

The work contains an introduction which is actually a current stage of research in the analyzed field.

The objectives proposed by the authors have been covered, the paper is adequately structured.

The research methodology presented by the authors reveals a knowledge of the researched field.

The results obtained from the statistical analysis using the SPSS software are good.

Some questions for the authors:

-          Related to the 2 scenes - other participants were also taken into account (vehicles, cyclists, pedestrians, road infrastructure - lane width, weather conditions). All these parameters influence the analysis of the human factor.

-          There is no table with the results of the 31 participants.

-          Who are F3, F4, P3, P4 and O2 from table 1

-          The title of a table is passed above it and not below it

-          What are the results of experiment 46, as specified in line 308 (...as shown in experiment No. 46)?

-          Not all bibliographic references are included in the text (from 38 – 58)

The conclusions drawn are general ones. I suggest the objective presentation of the conclusions. For example: double depth HUD which is the percentage of mental load reduction.

Author Response

Thank you very much for taking the time to review this manuscript.

Comments 1:

Related to the 2 scenes - other participants were also taken into account (vehicles, cyclists, pedestrians, road infrastructure - lane width, weather conditions). All these parameters influence the analysis of the human factor.

Response 1:

Many thanks for the comment. In order to reduce additional experimental factors and increase the reliability of experimental results, the experimental scenes are the same, setting as a monotonous straight single-lane road with a length of 200km and a width of 3.72m. There is a streetlight on the left and a speed limit sign of 100km/h on the right.

Comments 2:

There is no table with the results of the 31 participants.

Response 2:

Thank you for your reminder. The data for all tables are the averaged results from the 31 participants.

Comments 3:

Who are F3, F4, P3, P4 and O2 from table 1

Response 3:

Thank you for your reminder. We have supplemented the description of the positions of F3, F4, P3, P4, and O2 in lines 204-211.
In Table 1, F3, F4, P3, P4, and O2 refer to different EEG electrode positions:

F3: Left frontal lobe

F4: Right frontal lobe

P3: Left parietal lobe

P4: Right parietal lobe

O2: Right occipital lobe

Comments 4:

The title of a table is passed above it and not below it

Response 4:

Thank you for your comment. All table titles have been corrected for their positions.

Comments 5:

What are the results of experiment 46, as specified in line 308 (...as shown in experiment No. 46)?

Response 5:

Thank you for your reminder. The paragraph does not refer to Experiment No. 46 but indicates that at 46 minutes into the experiment, single-depth HUD shows higher visual fatigue during this period. The manuscript content has been revised.

Comments 6:

Not all bibliographic references are included in the text (from 38 – 58)

Response 6:

Thank you for your reminder. We have updated and organized the references in the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors The topic addressed in the article is topical. The structure of the article is correct. However, I would ask the authors to answer the following questions.   What was the criterion for the selection of study participants?   Were differences observed in the results obtained for men and women? If so, which ones?   What was the driving experience of the test persons (how many years had they held a driving licence)?   Were there professional drivers among the test persons or not?   Was the effect of weather conditions, time of year and time of day on the test results investigated? If so, what?   What does it mean that the persons met the minimum vision requirements?

Author Response

The topic addressed in the article is topical. The structure of the article is correct. However, I would ask the authors to answer the following questions. 

Response :

Thank you very much for taking the time to review this manuscript.

Many thanks for the comment. We will address the questions you have raised below.

Comments 1:

What was the criterion for the selection of study participants?

Response 1:

Those who hold a driver's license from the Republic of China and have at least one year of road driving experience meet the vision standards of the Republic of China for obtaining a driver's license. Those with short-sightedness must wear glasses or contact lenses for correction. The basic requirement is that the limbs must be able to drive normally and be between 20 and 60 years old. 

Comments 2:

Were differences observed in the results obtained for men and women? If so, which ones?

Response 2:

There are no differences between men and women.

Comments 3:

What was the driving experience of the test persons (how many years had they held a driving license)?

Response 3:

 Table: basic driving information

	N	Min	Max	Average
Age	31	20.0	56.0	27.0
Years Had Driving License	31	1.0	36.0	5.9

Comments 4:

Were there professional drivers among the test persons or not?

Response 4:

There are no professional drivers in this experiment.

Comments 5:

Was the effect of weather conditions, time of year and time of day on the test results investigated? If so, what?

Response 5:

In order to reduce additional experimental factors and increase the reliability of experimental results, the experimental scenes are the same, setting as a monotonous straight single-lane road with a length of 200km and a width of 3.72m. There is a streetlight on the left and a speed limit sign of 100km/h on the right.

Comments 6:

What does it mean that the persons met the minimum vision requirements?

Response 6:

The experiment excluded color blindness and those with nearsightedness who meet the minimum vision standard for obtaining a driver's license without correction.

Reviewer 3 Report

Comments and Suggestions for Authors

1. The article raises an interesting point about the impact of single-depth and dual-depth HUD vehicle windscreen displays on driver fatigue, the way content and information are absorbed, and distraction from the road. The topic is very interesting and timely. Many vehicles have such displays, and the overall aim is to reduce the distraction of the driver's eyes from the road by observing displays that are in line with the eyes watching the road.

   The authors have conducted a very extensive literature review (58 items), presenting the work, research, and functionality of HUD displays. The citations are logical and relevant to the content described. The research problem defined was to compare the usability of a display with a single display depth of 2.5 m and a dual display depth of 2.5 m and 6 m. The evaluation criteria were the degree of fatigue of the test subjects and the analysis of post-test survey questionnaires. The authors developed an interesting research procedure and implemented it correctly.

   A study group (31 people) was selected and subjected to verification (visual aptitude, absence of defects). The simulator test was developed based on the data of a real vehicle, and two test scenarios were created: urban driving and a long road stretch. Scenarios of the environment and driving physics were developed. The manner in which the thesis test was performed was correct, taking into account the adaptation process to the simulation conditions. It should be noted that the test method was approved by the relevant authorities.

   Eye blink frequency was assessed as an indication of the degree of fatigue, brainwave activity as the effort and workload required to perform observational activities, and the Questionnaire Test as part of the assessment of the degree of fatigue and frustration with visual work. Specialized hardware and software (Microsoft HoloLens2, BIOPAC MP150 System, NASA-TLX) were used. To evaluate the collected data, statistical methods were chosen to establish normal distributions, based on which the measurement results will be related to reference data. A number of interesting relationships were identified in the study. The results were subjected to a critical appraisal, and further work was identified, which the authors believe should be carried out to increase the reliability of the assessment in a wider range of real-world cases.

   In general, it was pointed out that, in most cases, a double-depth display tires the driver less and absorbs their attention better, and the test questionnaires confirmed this relationship. At the same time, it was indicated that when the observation time is prolonged, the observation of the double-depth display can be more tiring (brainwave levels, blink frequency). This phenomenon was explained by the way in which information is displayed using a laser diode that causes speckling and worsens vision. The optimum amount of information displayed and where it should be located (speed, 2.5 m speed limit, 6 m navigation, eye adapted to full visual acuity) was also indicated. The results of the study are summarized in tables and graphs that are easy to read. Comments were made, and causation was determined.

   Overall, the whole research process was conducted fairly and in a multifaceted manner. The results are interesting and form the basis for further work and, consequently, for the development of the indicated solutions for motorization.

    

   Critical comments:

   1. Error: In Table 2, Blink Count Time Change Statistics table - in two columns, "single-depth" should be in one dual-depth (HUD display type).
   2. In Figure 10, NASA-TLX Working Load Comparison Chart - units are missing on the x-axis.
   3. To make the test in the simulator comparable, room darkening was introduced, causing the HUD display not to be subjected to external lighting. For the adopted test methodology, this is a valid assumption. However, under real-world conditions, the driver is subjected to numerous glares, and the effect of this light on the displayed information could be considered in future studies

Author Response

Comments 1:

Error: In Table 2, Blink Count Time Change Statistics table - in two columns, "single-depth" should be in one dual-depth (HUD display type).

Response 1:

Thank you for your reminder. The errors have been corrected in the manuscript.

Comments 2:

In Figure 10, NASA-TLX Working Load Comparison Chart - units are missing on the x-axis.

Response 2:

Thank you for your reminder. The x-axis is “Deep of Projection”.

Comments 3:

To make the test in the simulator comparable, room darkening was introduced, causing the HUD display not to be subjected to external lighting. For the adopted test methodology, this is a valid assumption. However, under real-world conditions, the driver is subjected to numerous glares, and the effect of this light on the displayed information could be considered in future studies.

Response 3:

Many thanks for the comment. In future research, the impact of light on displayed information will be evaluated to achieve better results.