Modulation of In-Vehicle Display Parameters to Reduce Motion Sickness^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper is a study that proposes and identifies a method for mitigating motion sickness for in-vehicle media viewing by dynamically adjusting the FOV on the in-vehicle display based on vehicle movement.

Dear authors, I believe that in this article there are some arguments regarding the treated subject. Research, studies and experimental results are valuable, but the definition and description need to be improved. I think that your article will be interesting to the readers of Electronics journal and useful to some of them.

Regarding the content of the article I have the following remarks/questions:

Please explain from the beginning what is the connection with article 24, why is not cited that paper?!

In my opinion, a description of the sections is recommended in the Introduction chapter to have a better understanding of the presentation.

I think that all the mathematical relations (equations) should be checked again to have a guarantee of their correctness. Please explain equation 3!! Equations that come from bibliographic sources must have a reference (must be cited)!!

For a better understanding of the presentation, a list of acronyms must be inserted.

The article does not follow the provided template:

In order to have a better understanding of this work the figures must be placed in the main text near to the first time they are cited and, very important, figure should be placed in the text after it was first quoted (cited). For example: figures 1, 2, 8, 9 has no citation.

The space between paragraphs should be set according to the template. Please correct for all (for example lines 34, 41 and so on....)

The format of References paragraph is correctly defined? If not please correct. All references must be cited in the text and must be numbered in order of appearance (including citations in tables and legends).

 

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Comments 1: Please explain from the beginning what is the connection with article 24, why is not cited that paper?!  
In my opinion, a description of the sections is recommended in the Introduction chapter to have a better understanding of the presentation.

Response 1: Agree. We have included a citation to the conference paper [24] in the Introduction to clarify its relationship with the present journal version. We have also revised the final paragraph of the Introduction to describe the structure of the paper, specifying the contents of each section for improved clarity.

Comments 2: I think that all the mathematical relations (equations) should be checked again to have a guarantee of their correctness. Please explain equation 3!! Equations that come from bibliographic sources must have a reference (must be cited)!!

Response 2: Agree. We have carefully rechecked all mathematical equations (Equations 1 to 3) to ensure their correctness.

We have added a clarification near Equation (3) to explain that it is a custom normalization method used to compare the participant’s motion sickness score in each condition relative to their own average and maximum values. This method was selected to enable consistent intra-participant comparisons in the context of only three available conditions.

Equations (1) and (2) were defined as part of the experimental logic in this study. Regarding Equation (3), although its structure is similar to standard normalization forms found in the literature, it was independently constructed for this experiment and is not directly derived from a bibliographic source. Therefore, no citation is required.

Comments 3: For a better understanding of the presentation, a list of acronyms must be inserted.

Response 3: Agree. A list of all abbreviations used in the manuscript has been inserted. This list includes terms such as VR, FOV, and SSQ, which appear throughout the paper.

Comments 4: In order to have a better understanding of this work the figures must be placed in the main text near to the first time they are cited and, very important, figure should be placed in the text after it was first quoted (cited). For example: figures 1, 2, 8, 9 has no citation.

The space between paragraphs should be set according to the template. Please correct for all (for example lines 34, 41 and so on....)

The format of References paragraph is correctly defined? If not please correct. All references must be cited in the text and must be numbered in order of appearance (including citations in tables and legends).

Response 4: All figures and tables are now cited in the main text near their first appearance, and the paragraph spacing has been adjusted to follow the journal’s formatting guidelines. The reference format has also been reviewed and aligned with the required style.

Reviewer 2 Report

Comments and Suggestions for Authors

Review of “A Study on the Motion Sickness Reduction Technology in Vehicle Media Environment”

 

The authors aimed to assess the effects of brightness and field of view (FOV) on motion sickness (MS) in passengers who sit in the rear of an autonomous vehicle. To do so, they have created a nice virtual environment of a passenger car interior. Seemingly attached to the head rest of the front passenger seat, a tablet-sized display was mounted, which could display some unspecified video content. The video could be occluded in the periphery of the display (small FOV), and it could be reduced in brightness. On each of three separate days, the authors tested 36 subjects in all three monitor conditions (not sure why they call it cases). Condition 1 was the standard monitor, Condition 2 the adjusted brightness, and Condition 3 the FOV-adjustment. In conditions 2 and 3, the respective monitor adjustments were performed as a function of the car’s linear and angular accelerations. Whenever such occurred, the FOV was reduced or the brightness was dimmed. The results are interpreted to show a reduction in MS Conditions 2 and 3.

 

This is a nice study, however, we cannot recommend that it be published in its current form. There are three areas where major improvements are required.

 

1. Theoretical background: It is well known that the amount of optical flow in a fixed-base simulator is correlated positively with MS.  This work should be considered. For instance, Nooij at al. investigated the role of angular optical flow and the associated feeling of vection, which can modulated MS (see Nooij, S. A. E., Pretto, P., Oberfeld, D., Hecht, H., & Bülthoff, H. H. (2017). Vection is the main contributor to motion sickness induced by visual yaw rotation: Implications for conflict and eye movement theories.  PLoS ONE, 12(4), e0175305. doi.org/10.1037/xhp000047310.1371/journal.pone.0175305).

Likewise, there is work showing that MS was not affected by display parameters such as brightness or contrast (see Shahal, A., Hemmerich, W., & Hecht, H. (2016). Brightness and contrast do not affect visually induced motion sickness in a passively-flown fixed-base flight simulator. Displays, 44, 5 – 14. doi.org/10.1016/j.displa.2016.05.007).

 

The reader deserves a discussion of these prior findings and a good explanation why the authors use the stimuli that they do.

 

2. The methods are described very poorly in many places, to the extent that it becomes impossible to figure out what exactly the stimulus was. Here is our reconstruction: The eye-point corresponded to that of a passenger in the rear seat. Thus, the only visual information revealing the motion and accelerations of the car were the parts of the outside world that became visible, and were occluded intermittently based on the subjects’ head movements, they could see next to seats and dash when looking outside. What were the instructions where to look? Obviously, when there is a video playing on the tablet screen, observers will look at it. Was care taken that they fixated the tablet at all times? If so, very little peripheral visual information of the outside world was available. This would explain the relatively low levels of MS even in the standard monitor condition.

 

2. 1 What was the vestibular stimulus? You state that you “employ a motion simulator to simulate real vehicle vibrations”, but nowhere can information be found that specifies the simulator. Was it a motion platform? How did it move? How did it vibrate? Was the subject physically accelerated or was the stimulus mainly visual. This is of critical importance to know.

 

2.2 The SSQ is problematic in many respects and it is not interval scaled. Strictly speaking, it provides only categorical information and does not differentiate very well. Having said this, it has proven to be astonishingly robust. Its main problem is that scores that barely exceed 30 or 40 indicate more or less very slight and almost negligeable symptoms. The SSQ score is produced by answers ranging from none, slight, moderate, to severe. Per subscale, four “slight” responses produce a score between 30 and 45.  The values reported by the authors range between 24 and 52 on Day2 and Day3. Thus, MS was at best slight on half of the symptoms and none on the other half. The SSQ scores are thus highly problematic when MS is slight. The SSQ is an extremely skewed scale ranging from 0 to about 250. Some items enter into the sum score several times. For future studies, we encourage the use of a continuous rating scale that has clear anchors on both ends and that can be treated as an interval scale. (see e. g. Keshavarz, B., Hecht, H. (2011). Validating an efficient method to quantify motion sickness. Human Factors, 53(4), 415 – 426. doi.org/10.1177/0018720811403736.)

 

3. Data analysis: Data from Day 1 were thrown out. Why on earth? We want to know these values per day. The least you should do, is plot the data from all days and all conditions. It looks to us that on Day 2 and 3 there basically was none or only very slight MS in all conditions. This is hardly any MS to worry about. Presumably, on Day 1 subjects did experience more MS. This would be interesting, also with regard to quick adaptation effects.

 

3.2 Data normalization: This should only be done when desperate, and then only in addition to the non-normalized data. One should have significance tests on the non-normalized data. And yes, MS-data are always rather noisy because of large individual differences. The normalized Anova produced suspiciously large F-values. The reader need to be provided with the full set of Anova parameters, when these are reported, including degrees of freedom and effect size parameters.

 

3.3 The second experiment with only 5 subjects should not be statistically analyzed. There are no meaningful tests for such a small sample.

 

Minor points:

There is also an incorrect statement in lines 148ff: The vestibular system only transduces acceleration, be they linear or angular. In both cases does it fail to detect constant motion.

 

Figure 2 should make it more obvious that there were 3 sessions per day, and that they were repeated on 3 different days.

 

Lines 247ff How were there MS levels among experimenters? Did the experimenters get sick while observing the subjects?

 

In sum, the reader does not know what exactly the stimulus looked like and is in no position to evaluate under what conditions a restriction of FOV and a reduction of brightness might be useful. Also, it would be important to know if subjects did notice the visual monitor manipulations and whether they would put up with them when watching a movie or when reading a story on the tablet. As is, the manuscript is not sufficiently informative and should not be published.

 

Author Response

Comments 1: Theoretical background: It is well known that the amount of optical flow in a fixed-base simulator is correlated positively with MS. This work should be considered. For instance, Nooij at al. investigated the role of angular optical flow and the associated feeling of vection, which can modulated MS (see Nooij, S. A. E., Pretto, P., Oberfeld, D., Hecht, H., & Bülthoff, H. H. (2017). Vection is the main contributor to motion sickness induced by visual yaw rotation: Implications for conflict and eye movement theories. PLoS ONE, 12(4), e0175305. doi.org/10.1037/xhp000047310.1371/journal.pone.0175305).

Likewise, there is work showing that MS was not affected by display parameters such as brightness or contrast (see Shahal, A., Hemmerich, W., & Hecht, H. (2016). Brightness and contrast do not affect visually induced motion sickness in a passively-flown fixed-base flight simulator. Displays, 44, 5 – 14. doi.org/10.1016/j.displa.2016.05.007).

The reader deserves a discussion of these prior findings and a good explanation why the authors use the stimuli that they do.

Response 1: Agree. We have revised the Introduction (and Related Research) to include findings from Nooij et al. (2017) and Shahal et al. (2016). While prior studies reported that static brightness or contrast levels had little effect on motion sickness, our study investigates whether dynamically adjusting brightness and FOV in real-time, synchronized with vehicle motion, could lead to different outcomes. This dynamic approach contrasts with the static conditions in earlier fixed-base simulator studies and serves as a key rationale for our experimental design. [page number 2, 1. Introduction, and line 39~44] "Previous studies have shown that motion sickness (MS) in visual environments is closely related to optical flow, particularly in fixed-base simulators. For instance, Nooij et al.[14] found that vection induced by angular optical flow is a primary contributor to MS, supporting theories of sensory conflict and eye movement. Conversely, Shahal et al.[15] reported that visual display parameters such as brightness and contrast did not significantly affect MS in a passively flown simulator."

Comment 2: The methods are described very poorly in many places, to the extent that it becomes impossible to figure out what exactly the stimulus was. Here is our reconstruction: The eye-point corresponded to that of a passenger in the rear seat. Thus, the only visual information revealing the motion and accelerations of the car were the parts of the outside world that became visible, and were occluded intermittently based on the subjects’ head movements, they could see next to seats and dash when looking outside. What were the instructions where to look? Obviously, when there is a video playing on the tablet screen, observers will look at it. Was care taken that they fixated the tablet at all times? If so, very little peripheral visual information of the outside world was available. This would explain the relatively low levels of MS even in the standard monitor condition.

Response 2: We have revised the Experimental Design section to provide a clearer explanation of the visual stimulus and participant instructions. Participants were seated in a fixed position corresponding to the rear seat of a vehicle and were instructed to maintain visual fixation on the in-vehicle display throughout each trial. The vehicle interior and exterior environments were implemented using Unreal Engine. During the experiment, participants were exposed not only to the screen content but also to peripheral visual input of the virtual environment through areas such as the front interior space and the right-side rear window. These elements allowed participants to perceive partial motion in their peripheral vision. [page number 5, 3. Experimental Methods, and line 155~158] "Within this environment, similar to real-world contexts, changes in the external surroundings, user motion, and display dynamics interact in complex ways (Figure~\ref{fig-movement}). To build such a simulation, we modeled not only the vehicle’s exterior and interior but also the media environment. " [page number 5, 3. Experimental Methods, and line 171~178] "In the virtual environment, participants were seated in a fixed position corresponding to the rear seat of a vehicle and were instructed to maintain visual fixation on the in-vehicle display throughout each trial(Figure 3). The virtual vehicle interior and exterior environments were implemented using Unreal Engine 4.27. Although participants primarily focused on the display content, peripheral motion of the virtual environment could be perceived through the front-facing windshield and the right-side window. This setup allowed participants to receive partial peripheral visual motion cues during the task. "

Comment 2.1: What was the vestibular stimulus? You state that you “employ a motion simulator to simulate real vehicle vibrations”, but nowhere can information be found that specifies the simulator. Was it a motion platform? How did it move? How did it vibrate? Was the subject physically accelerated or was the stimulus mainly visual. This is of critical importance to know.

Response 2.1: We have added detailed information about the motion platform used. A three-degrees-of-freedom (3-DOF) motion simulator was employed, capable of reproducing roll, pitch, and heave movements. The platform delivered synchronized physical feedback—such as tilting and vibration—alongside the visual effects that dynamically responded to virtual vehicle motion. These details are now described in the Experimental Setup section. [page number 4, 3. Experimental Methods, and line 140~154] "In our study, we constructed a VR environment that closely mimics real driving conditions. In addition, motion stimuli were designed to be synchronized with virtual vehicle movement in order to emulate vestibular stimulation. Figure1 illustrates the basic operation of the motion simulator used for synchronization, which operates along three axes: roll, pitch, and heave. To simulate the vestibular stimulation experienced in real vehicles, the motion simulator was configured to respond only to changes in acceleration. By comparing the current and previous acceleration values, the system determines whether the vehicle is moving at a constant speed—indicated when the two values are equal. In actual driving scenarios, passengers feel a momentary shift in body posture when movement begins or when speed changes occur. As the vehicle continues to move at a constant velocity, the body gradually returns to a neutral position from its initial tilted state. Similarly, the motion simulator replicates this response by tilting according to the direction and intensity of the vehicle's acceleration at the onset of motion. As the motion continues and the difference between the current and previous acceleration diminishes, the simulator gradually returns from its tilted position to the neutral posture."

Comment 2.2: The SSQ is problematic in many respects and it is not interval scaled. Strictly speaking, it provides only categorical information and does not differentiate very well. Having said this, it has proven to be astonishingly robust. Its main problem is that scores that barely exceed 30 or 40 indicate more or less very slight and almost negligeable symptoms. The SSQ score is produced by answers ranging from none, slight, moderate, to severe. Per subscale, four “slight” responses produce a score between 30 and 45.  The values reported by the authors range between 24 and 52 on Day2 and Day3. Thus, MS was at best slight on half of the symptoms and none on the other half. The SSQ scores are thus highly problematic when MS is slight. The SSQ is an extremely skewed scale ranging from 0 to about 250. Some items enter into the sum score several times. For future studies, we encourage the use of a continuous rating scale that has clear anchors on both ends and that can be treated as an interval scale. (see e. g. Keshavarz, B., Hecht, H. (2011). Validating an efficient method to quantify motion sickness. Human Factors, 53(4), 415 – 426. doi.org/10.1177/0018720811403736.)

Response 2.2: We acknowledge the limitations of the SSQ, including its non-interval scaling and tendency to yield elevated scores even for slight symptoms. Nonetheless, the SSQ remains one of the most widely used and validated instruments for assessing motion sickness, particularly in VR and simulator-based studies.

In our study, although a VR environment was used, it was designed to replicate a relatively static scenario where participants remained fixed in the rear seat of a vehicle. Unlike dynamic VR gaming environments that often induce stronger symptoms, our controlled setup naturally led to lower SSQ score distributions. Given the SSQ’s broad scoring range that accommodates both mild and severe symptoms, the relatively low scores observed in our study are consistent with the static and visually constrained conditions employed. This context should be taken into account when interpreting the results.

Furthermore, we recognize that the SSQ relies on self-reported responses, which are subject to individual variation in perception and reporting. To mitigate this issue and account for differences in individual response tendencies, we conducted ANOVA analysis based on normalized scores (Equation 3), allowing for comparisons that consider within-subject variability.

We agree that future studies would benefit from incorporating continuous or self-anchored rating scales as suggested (e.g., Keshavarz & Hecht, 2011), especially when measuring low-intensity symptoms in controlled settings. [page number 13, 5.2.1. Motion Sickness Analysis (SSQ Results), and line 320~321] "This normalization approach allows for individual response tendencies to be accounted for, enabling fair comparisons across participants."

Comment 3: Data analysis: Data from Day 1 were thrown out. Why on earth? We want to know these values per day. The least you should do, is plot the data from all days and all conditions. It looks to us that on Day 2 and 3 there basically was none or only very slight MS in all conditions. This is hardly any MS to worry about. Presumably, on Day 1 subjects did experience more MS. This would be interesting, also with regard to quick adaptation effects.

Response 3: We excluded Day 1 data from the ANOVA analysis due to strong adaptation effects and increased variability observed during initial exposure. Motion sickness scores were generally higher on Day 1, but became more stable on Days 2 and 3, indicating that participants quickly adapted to the experimental environment. Including Day 1 would have introduced time-dependent variability that could confound the evaluation of display condition effects, which was the primary objective of this study. Although raw SSQ data from all three days are presented in the figures for transparency, Day 1 was excluded from statistical analysis.

To clarify this point, we have added a description in the manuscript and included figures showing the distribution of SSQ scores across all three experimental days, as well as the combined scores from Days 2 and 3 used in the main analysis. [page number 12, 5.2.1. Motion Sickness Analysis (SSQ Results), and line 307~311] "Participants showed relatively higher motion sickness scores on Day 1, but their responses stabilized on Days 2 and 3, indicating a possible adaptation effect[25]. To minimize the impact of such time-dependent variability and ensure clearer condition-based comparisons, the analysis was focused on data from the latter two days(Figure 12)."

Comment 3.2: Data normalization: This should only be done when desperate, and then only in addition to the non-normalized data. One should have significance tests on the non-normalized data. And yes, MS-data are always rather noisy because of large individual differences. The normalized Anova produced suspiciously large F-values. The reader need to be provided with the full set of Anova parameters, when these are reported, including degrees of freedom and effect size parameters.

Response 3.2: We understand the reviewer’s concern regarding the use of normalized data and the potentially large F-values. In our study, normalization was applied to address substantial individual differences in motion sickness scores, which can obscure condition-specific effects in group-level analysis. This approach aimed to reduce inter-subject variability and allowed within-subject comparisons to be made more interpretable, which was especially important given the limited number of test conditions per participant.

While raw score-based analysis was not included in the manuscript, we explored various forms of the data internally, including unnormalized versions, and found similar trends.

We corrected some typographical errors in the ANOVA summary table, and for transparency, we have included the original analysis output (based on Day 2 and Day 3, excluding four participants) in Appendix A, which contains SS, df, MS, and full F-value computation details. [page number 17, Appendix A, and line 448]

Comment 3.3: The second experiment with only 5 subjects should not be statistically analyzed. There are no meaningful tests for such a small sample.

Response 3.3: We acknowledge the reviewer’s concern regarding the limited sample size in the second experiment (n = 5). The objective of this second experiment was exploratory, aiming to observe general trends in motion sickness under modified display and motion conditions.
We clarified in the manuscript that statistical interpretation was limited due to the small sample size, and the analysis focused on identifying observable trends rather than drawing inferential conclusions. [page number 14, 5.3. Secondary Experiment Results, and line 356~358] "Although statistical testing was limited due to the small sample size (n = 5), SSQ score patterns were reviewed across the three days to observe consistent trends in motion sickness under modified display conditions."

Comment 4: There is also an incorrect statement in lines 148ff: The vestibular system only transduces acceleration, be they linear or angular. In both cases does it fail to detect constant motion.

Response 4: We acknowledge that the original sentence did not sufficiently convey the vestibular system’s functional mechanism. The sentence has been revised to more accurately reflect the vestibular system’s physiological behavior. In the revised version, we clarified that the vestibular system responds only to acceleration—both linear and angular—and not to constant motion. [page number 7, 4. Algorithms, and line 227~229] "Regarding angular motion, the primary trigger is the initial change in angular velocity (i.e., angular acceleration), as the vestibular system responds only to acceleration, and sustained angular velocity becomes perceptually negligible over time. "

Comment 5: Figure 2 should make it more obvious that there were 3 sessions per day, and that they were repeated on 3 different days.

Response 5: We acknowledge the need for greater clarity in Figure 2. The updated figure now includes clearer labels and structure to indicate that each participant completed three sessions per day across three consecutive days. [page number 7, 3.2. Experimental Procedure, and line 202]

Comment 6: Lines 247ff How were there MS levels among experimenters? Did the experimenters get sick while observing the subjects?

Response  6: Thank you for pointing this out. The original phrasing was misleading. The term "experimenters" was mistakenly used where "participants" was intended. We have revised the sentence in the manuscript to clarify that the normalization was applied due to large individual differences in participants’ motion sickness responses, not due to effects on the experimenters. [page number 12~13, 5.2.1. Motion Sickness Analysis (SSQ Results), and line 312~314] "Additionally, due to large individual differences in participants’ motion sickness responses, normalization was applied to the means of Day 2 and Day 3 data."

Comment 7: Also, it would be important to know if subjects did notice the visual monitor manipulations and whether they would put up with them when watching a movie or when reading a story on the tablet. 

Response 7: We note that the manuscript already addresses this concern; participant interviews indicated that most subjects were unaware of the visual manipulations, suggesting a positive reception and potential acceptability of the applied effects. [page number 15, 5.4. Implications of Immersion and Visual Adjustments, and line 385~386] "Interviews with participants further confirmed that they were largely unaware of the visual effects, indicating a positive outcome."

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is well-structured, clearly describing objectives, methodology, and results. Visual aids like figures and tables effectively support the experimental data, but some sections, particularly the algorithm flowcharts, could benefit from more detailed explanations for improved clarity.

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The experiments are scientifically robust, employing standardized questionnaires (e.g., MSSQ, SSQ, and PQ) and rigorous statistical analyses to validate the findings. However, the sample size for the secondary experiment (n=5) is relatively small, limiting the generalizability of those specific results.

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The comprehensive references cover seminal and recent works on motion sickness, VR environments, and in-vehicle media. However, a few citations, such as those dated before 2010, might benefit from replacing or supplementing newer studies to reflect current advancements.

Author Response

Comment 1: The manuscript is well-structured, clearly describing objectives, methodology, and results. Visual aids like figures and tables effectively support the experimental data, but some sections, particularly the algorithm flowcharts, could benefit from more detailed explanations for improved clarity.

Response 1: Thank you for the suggestion. To improve clarity, we have expanded the accompanying descriptions for Figures 6 and 8 in the manuscript. These additions aim to help readers more easily understand the structure and logic of the flowcharts. [page number 8, 4. Algorithms, and line 235~238] "Figure 6 depicts the overarching algorithm where these adjustments are implemented, summarizing the conditional logic used to trigger brightness and FOV changes based on angular and linear motion." [page number 9, 4.2. Application of Effects and Algorithm Flowcharts, and line 271~278] "Figures 8 and 9 present the flowcharts of the algorithms used in the pilot, main, and secondary experiments. 
In Figure8, the pilot and main experiments utilize only angular velocity to dynamically adjust brightness and FOV according to changes in the vehicle’s angular velocity. 
Angular velocity is calculated every 0.3 seconds for an angle, 'd_i' using a vector variable that dynamically changes in response to the vehicle’s direction. Changes in angular velocity are measured at regular intervals during this process. The figure outlines the repeated angle tracking, dot product computation, and threshold comparisons used to determine visual adjustments. "

Comment 2: The experiments are scientifically robust, employing standardized questionnaires (e.g., MSSQ, SSQ, and PQ) and rigorous statistical analyses to validate the findings. However, the sample size for the secondary experiment (n=5) is relatively small, limiting the generalizability of those specific results.

Response 2: We agree with the reviewer’s observation regarding the limited sample size in the secondary experiment (n=5). This experiment was exploratory in nature and intended to observe general trends rather than produce statistically generalizable findings. We also clarified in the manuscript that no formal inferential analysis was conducted, and interpretation was limited accordingly. [page number 14, 5.3. Secondary Experiment Results, and line 356~358] "Although statistical testing was limited due to the small sample size (n = 5), SSQ score patterns were reviewed across the three days to observe consistent trends in motion sickness under modified display conditions."

Comment 3: The comprehensive references cover seminal and recent works on motion sickness, VR environments, and in-vehicle media. However, a few citations, such as those dated before 2010, might benefit from replacing or supplementing newer studies to reflect current advancements.

Response 3: Thank you for the helpful suggestion. During the revision, we reviewed the reference list and supplemented it with several recent works to reflect current advancements in motion sickness and VR research. Where appropriate, older sources were retained if they were foundational or still widely cited.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors, I believe that in this article there are significant arguments regarding the treated subject. Research, studies and experimental results are valuable, correctly defined and presented. I think that your article will be interesting to the readers of Electronics and useful to some of them.

Author Response

Reviewer Comment: Dear authors, I believe that in this article there are significant arguments regarding the treated subject. Research, studies and experimental results are valuable, correctly defined and presented. I think that your article will be interesting to the readers of Electronics and useful to some of them.

Response: We sincerely thank the reviewer for the positive feedback and thoughtful evaluation.

Reviewer 2 Report

Comments and Suggestions for Authors

Review of revised manuscript “Modulation of in-Vehicle display parameters to reduce motion sickness”

 

The authors have responded well to most of our concerns and have produced an extensive revision. The manuscript now reads better, and missing information has been provided. However, there remain one important issue and a good number of smaller points that require further improvement:

 

Main issue:

We do not appreciate the answer to our comment 3. To reiterate: Data analysis: Data from Day 1 were thrown out. Why on earth? We want to know these values per day. The least you should do, is plot the data from all days and all conditions. It looks to us that on Day 2 and 3 there basically was none or only very slight MS in all conditions. This is hardly any MS to worry about. Presumably, on Day 1 subjects did experience more MS. This would be interesting, also with regard to quick adaptation effects.

 

The reader has a right to learn about the unstandardized SSQ-values for alle three days and all three conditions. Please provide them, for example in a table with SSQ values and their standard deviations.

 

Smaller points:

 

1. 17-31  one of the two paragraphs would be enough as an introduction to the topic.
2. 70-75  could be left out, the structure of a scientific paper should be clear anyway.

L 17-75 Overall, the introduction still seems a bit unstructured. The two relevant papers mentioned are now included, but it remains difficult to follow at times, because the content of the study is repeatedly interspersed.

 

The introduction could be tightened up by first offering a clear, concise introduction to the topic of motion sickness (MS) and explaining the core problem it represents in various contexts (travel, tourism, emerging VR applications, etc.). Following this, a focused summary of what has been done to address MS should be provided, including a brief review of existing studies on visual perception techniques and mitigation strategies. Finally, the introduction should then transition directly into describing what was done in the current study, highlighting the unique research question or innovative approach without reintroducing the general challenges of MS multiple times.

 

Clear hypotheses should be formulated at the end of the introduction. Strangely, they are mentioned too late in the Experimental Methods section (3.) at  l. 163-167

 

1. 117-131  it has been said several times in the introduction that media use leads to MS, no need to reiterate here
2. 133-158 -> This section describes the experimental setting well, presenting the use of a VR system in combination with a motion simulator to imitate real driving conditions. It would be helpful to explain more clearly which previous studies or empirical findings are relied upon when claiming that this setting adequately reflects the real-world experiences of the subjects. Specifically, it remains unclear to what extent the use of VR and 3DoF motion simulators (in the form of a seat) – despite the carefully designed stimuli (synchronized acceleration and tilt changes) – actually replicates the dynamic and complex driving environment realistically.

 

The 3DOF-seat is now better described. However, the reader should be able to replicated the experiment. Please provide degrees of chair tilt and acceleration.

 

1. 170-171  in the two consecutive sentences, it is said both times that the passenger was in the rear seat, omit one mention
2. 182 and the following: please always refer to the experimental conditions as such, calling it method is confusing.

 

Important: A section title with viewing environment would be helpful.  Could Fig. 4 be replaced with one showing the actual stimulus? It seems that all three conditions were displayed inside an HMD, correct? If so, what did the FOV-adjustment look like? Please illustrate the three conditions similar to Fig. 7.

 

 

1. 202 (figure 5)  The graphic is still hard to understand. Was the 10-minute block then carried out three times with two 15-minute breaks in between?
2. 313-318  It is described that the normalization is based on the mean values of the Day 2 and Day 3 data, but the calculation with A is done as an average over three test conditions; It is unclear whether all three measurement times are included in A and d or only those relevant for the analysis (Day 2 and Day 3). Please clarify whether and how the first measurement time point is included in the calculation, especially since it is excluded later. This clarification is important to avoid possible confusion when interpreting the standardized values.

 

Author Response

Comments 1: We do not appreciate the answer to our comment 3. To reiterate: Data analysis: Data from Day 1 were thrown out. Why on earth? We want to know these values per day. The least you should do, is plot the data from all days and all conditions. It looks to us that on Day 2 and 3 there basically was none or only very slight MS in all conditions. This is hardly any MS to worry about. Presumably, on Day 1 subjects did experience more MS. This would be interesting, also with regard to quick adaptation effects.
The reader has a right to learn about the unstandardized SSQ-values for alle three days and all three conditions. Please provide them, for example in a table with SSQ values and their standard deviations.
Response 1: We thank the reviewer for reiterating the importance of presenting the full dataset. As previously suggested, we have already incorporated the raw (unstandardized) Day 1 SSQ data into the manuscript. Specifically, Figure 12 now illustrates the SSQ results across all three experimental days and conditions. This addition was made in direct response to the earlier round of comments and was intended to ensure transparency regarding the observed adaptation effects. [page number 12, 5.2.1. Motion Sickness Analysis (SSQ Results), and line 297~298, Figure 12]

Comments 2: 17-31  one of the two paragraphs would be enough as an introduction to the topic.
70-75  could be left out, the structure of a scientific paper should be clear anyway.
L 17-75 Overall, the introduction still seems a bit unstructured. The two relevant papers mentioned are now included, but it remains difficult to follow at times, because the content of the study is repeatedly interspersed.
The introduction could be tightened up by first offering a clear, concise introduction to the topic of motion sickness (MS) and explaining the core problem it represents in various contexts (travel, tourism, emerging VR applications, etc.). Following this, a focused summary of what has been done to address MS should be provided, including a brief review of existing studies on visual perception techniques and mitigation strategies. Finally, the introduction should then transition directly into describing what was done in the current study, highlighting the unique research question or innovative approach without reintroducing the general challenges of MS multiple times.
Response 2: We appreciate the reviewer’s suggestions regarding the organization of the introduction. As our study addresses motion sickness mitigation through visual adjustments within a motion simulator environment, we structured the introduction to follow a progression from general visual perception techniques for motion sickness reduction, to hybrid environments using fixed-base simulators, and finally to FOV adjustment techniques, which in our study were limited to the display rather than the entire field of view. While this approach may have led to slight thematic overlap, we considered these elements necessary to provide the full context for our experimental approach. In response to the reviewer’s feedback, we have revised the introduction to improve clarity by removing the redundant structural explanation and consolidating several sections to reduce repetition. [page number 1~2, 1. Introduction, and line 17~70]

Comments 3: Clear hypotheses should be formulated at the end of the introduction. Strangely, they are mentioned too late in the Experimental Methods section (3.) at  l. 163-167
Response 3: As the hypotheses were already clearly stated at the end of the Introduction, as recommended, we have kept them in place and removed the redundant mention from Section 3 (Experimental Methods) to improve clarity and avoid repetition.

Comments 4: 117-131  it has been said several times in the introduction that media use leads to MS, no need to reiterate here
Response 4: The redundant content regarding media-induced motion sickness has been removed from this section to avoid repetition.

Comments 5: 133-18 -> This section describes the experimental setting well, presenting the use of a VR system in combination with a motion simulator to imitate real driving conditions. It would be helpful to explain more clearly which previous studies or empirical findings are relied upon when claiming that this setting adequately reflects the real-world experiences of the subjects. Specifically, it remains unclear to what extent the use of VR and 3DoF motion simulators (in the form of a seat) – despite the carefully designed stimuli (synchronized acceleration and tilt changes) – actually replicates the dynamic and complex driving environment realistically.
The 3DOF-seat is now better described. However, the reader should be able to replicated the experiment. Please provide degrees of chair tilt and acceleration.
Response 5: We thank the reviewer for the suggestion. To address this, we have added a sentence in the manuscript clarifying that the motion output was generated using the internal dynamics engine of the motion simulator, based on a maximum tilt configuration of ±10 degrees. [page number 5, 3. Experimental Methods, and line 160~162]

Comments 6: 170-171  in the two consecutive sentences, it is said both times that the passenger was in the rear seat, omit one mention
Response 6: Thank you for pointing this out. We have removed the redundant sentence to eliminate repetition. [page number 5, 3. Experimental Methods, and line 155~159]

Comments 7: Please always refer to the experimental conditions as such, calling it method is confusing.
Response 7: Thank you for the suggestion. To reduce confusion, we have standardized the terminology by consistently using the word “condition” throughout the manuscript. [page number 5~6, 3.1. Experimental Case, and line 167~179]

Comments 8: Important: A section title with viewing environment would be helpful.  Could Fig. 4 be replaced with one showing the actual stimulus? It seems that all three conditions were displayed inside an HMD, correct? If so, what did the FOV-adjustment look like? Please illustrate the three conditions similar to Fig. 7.
Response 8: Thank you for the suggestion. We have updated Figure 4 to include illustrations that show how the visual effects appear when applied, in order to better represent the stimulus conditions. [page number 6, 3.1. Experimental Case, and line 178~179, Figure 4]

Comments 9: 202 (figure 5)  The graphic is still hard to understand. Was the 10-minute block then carried out three times with two 15-minute breaks in between?
Response 9: Thank you for the comment. Yes, each participant completed three 10-minute sessions per day, each followed by a 15-minute break and questionnaires, over the course of three days. To improve clarity, we have revised the description in Figure 5 to more clearly reflect this structure. [page number 7, 3.2. Experimental Procedure, and line 189~190, Figure 5]

Comments 10: 313-318  It is described that the normalization is based on the mean values of the Day 2 and Day 3 data, but the calculation with A is done as an average over three test conditions; It is unclear whether all three measurement times are included in A and d or only those relevant for the analysis (Day 2 and Day 3). Please clarify whether and how the first measurement time point is included in the calculation, especially since it is excluded later. This clarification is important to avoid possible confusion when interpreting the standardized values.
Response 10: Thank you for pointing this out. We understand the confusion and would like to clarify that the normalization was conducted using only the data from Day 2 and Day 3. In this context, the term “three conditions” refers to the three experimental conditions—standard monitor, brightness adjustment, and FOV adjustment—not to the three experimental days. Each participant’s score was normalized based on their responses across these three conditions during Day 2 and Day 3 only. [page number 12~13, 5.2.1. Motion Sickness Analysis (SSQ Results), and line 299~306]

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

The alterations to the manuscript have improved it sufficiently. We have no further suggestions.

Typos:

Line 26: remove hyphen in "in-duced"

Line 168: space missing before "(Figure 4)

 

Line 385: capitalize "We developed ..."

Author Response

Comments: The alterations to the manuscript have improved it sufficiently. We have no further suggestions.
Typos:
Line 26: remove hyphen in "in-duced"
Line 168: space missing before "(Figure 4)
Line 385: capitalize "We developed ..."
Response: We sincerely thank the reviewer for the thoughtful and detailed feedback throughout the review process. We have corrected all the noted typographical issues, including the removal of the hyphen in “in-duced,” the insertion of the missing space before “(Figure 4),” and the capitalization of “We developed” in line 385. We deeply appreciate your careful attention to the clarity and quality of the manuscript. 

Author Response File: Author Response.pdf