PONE-D-24-19578CNN-LSTM based Emotion Recognition using Chebyshev Moment and K-fold Validation with Multi-Library SVMPLOS ONE

Dear Dr. Mahendran,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

ACADEMIC EDITOR: Thank you for submitting your manuscript to PLOSE ONE. We have received feedback from reviewers on your paper. While the reviewers acknowledge the potential of your work, they have raised several concerns that need to be addressed. In light of these comments, we invite you to submit a revised version of your manuscript that addresses the reviewers' concerns for further consideration. Please include a detailed response to each point raised by the reviewers, and clearly indicate the changes made in the manuscript.

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We look forward to receiving your revised manuscript.

Kind regards,

Qionghao Huang

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The study proposes a hybrid CNN-LSTM model using RESNET152 CNN and Multi-Library SVM for facial emotion recognition. The model incorporates Chebyshev moments for feature extraction and K-fold validation for performance evaluation. The approach aims to improve accuracy, recall, and precision compared to existing methods. Some issues need to be addressed in the following:

- Research Motivation: The motivation behind the study is not clearly articulated. The paper should explicitly state the research gap that the proposed method aims to address. It is recommended that the authors clearly and concisely present this aspect.

- Recent Works: In the related work section, it would be beneficial to include some recent related works such as ‘Face2nodes: learning facial expression representations with relation-aware dynamic graph convolution networks, INS, 2023’, ‘FER-CHC: Facial expression recognition with cross-hierarchy contrast, ASOC, 2023’, ‘Emotion recognition from large-scale video clips with cross-attention and hybrid feature weighting neural networks, ERPH, 2023’, and ‘Facial expression recognition with grid-wise attention and visual transformer, INS,2021’. This will provide readers with a more current understanding of the field.

- Choice of Network Modules: Most current models use Vision Transformers (ViT) as the backbone for visual tasks. The authors should explain why they chose CNN or LSTM for designing the network. What are the advantages of these network modules compared to the existing mainstream modules? It is suggested that the authors supplement this part with relevant explanations.

- Chebyshev Moments: The motivation for introducing Chebyshev Moments is unclear. Are there better alternatives in the same category? Additionally, the experimental section does not provide a good comparison with similar methods. It is recommended to justify this part.

- Datasets and Generalization: In the experimental section, it is suggested to include more common datasets to demonstrate the generalization of the proposed method on different models. Additionally, compare the proposed model with the latest models to highlight its advancements.

- Ablation Studies: It is recommended to conduct comprehensive ablation studies to show the impact of different modules on the model’s performance. Additionally, perform parameter sensitivity analysis to demonstrate the effect of different parameters on the model’s performance.

- Image Quality: The quality of the images in the paper is relatively low. It is suggested to optimize them, preferably using vector graphics.

Reviewer #2: 1- Author has mistakenly written vgg9 in the graph and tables instead vgg19. Kindly correct it.

2-Could you elaborate on the specific criteria used for the manual filtering of the FER2013 dataset? How were factors such as contrast, brightness, and image angle quantitatively assessed during this process?

3-Why did you choose the Gaussian Filter and Chebyshev Moment for feature extraction? How do they compare to other commonly used feature extraction methods in the context of facial expression recognition?

4-In your training methodology, you combined CNN, LSTM, and ResNet152. Could you provide more insights into how these architectures complement each other in this specific application? What advantages does the combined model offer compared to using CNN or ResNet152 alone?

5-What is the advantage of using a Multi-library SVM classifier as the final classification step? How does it perform compared to traditional SVM or other classification methods like softmax?

6-Why did you manually select and filter the dataset? On what specific criteria were the images discarded, and what were the reasons for eliminating certain images?

7-Please improve the quality and symmetry of figures no 9, 12, 13, and 14.

8- The purpose of your paper is not clearly stated in the abstract. Please revise the abstract to indicate that the paper focuses on analyzing the driver's facial expressions to determine their mood or emotional state while driving. This will help readers quickly understand the core objective of your study and its relevance to driver behavior monitoring and safety.

9- What is the connection between facial expressions and the driver's sleepiness? Are closed eyes considered part of facial expressions in your analysis, or are they treated separately? How do you address the relationship between facial expressions and drowsiness in your study?

10- Many references in the paper are outdated. Please update the references to include more recent sources, preferably from 2020 to 2024, to ensure the research is aligned with the latest developments in the field

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Reviewer #1: No

Reviewer #2: No

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PONE-D-24-19578R1CNN-LSTM based Emotion Recognition using Chebyshev Moment and K-fold Validation with Multi-Library SVMPLOS ONE

Dear Dr. Mahendran,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

ACADEMIC EDITOR: Thank you for submitting your manuscript to PLOS ONE. We have received feedback from reviewers on your paper. The reviewers acknowledge the improvements made in your work and appreciate the potential it holds. However, they have identified a few areas that require further refinement. In light of these comments, we invite you to submit a revised version of your manuscript that addresses the reviewers' concerns for further consideration. Please include a detailed response to each point raised by the reviewers, and clearly indicate the changes made in the manuscript.

==============================

Please submit your revised manuscript by Feb 28 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

• A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Qionghao Huang

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #3: (No Response)

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: (No Response)

Reviewer #3: (No Response)

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: (No Response)

Reviewer #3: (No Response)

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: (No Response)

Reviewer #3: (No Response)

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: (No Response)

Reviewer #3: (No Response)

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The author's response has addressed my concerns on this paper, and I recommend an acceptance of this paper.

Reviewer #3: 1. The Introduction contains excessive content focused on automotive driving.

2. Line 39 and 70 lack proper punctuation at the end.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #3: No

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[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

CNN-LSTM based Emotion Recognition using Chebyshev Moment and K-fold Validation with Multi-Library SVM

PONE-D-24-19578R2

Dear Dr. Mahendran,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. If you have any questions relating to publication charges, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Alessandro Bruno, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Dear Authors,

You've worked out all the residual minor issues that were raised in the previous peer-review step.

Your paper is now ready for acceptance.

Kind regards,

A.B.

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #3: (No Response)

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: (No Response)

Reviewer #3: (No Response)

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: (No Response)

Reviewer #3: (No Response)

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: (No Response)

Reviewer #3: (No Response)

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: (No Response)

Reviewer #3: (No Response)

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The author's response has addressed my concerns on this paper, and I recommend an acceptance of this paper.

Reviewer #3: (No Response)

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #3: No

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