An open-source closed-loop Virtual Reality system to investigate social interactions and collective behavior in fish

Stéphane Sanchez; Ramón Escobedo; Renaud Bastien; Boris Lenseigne; Audrey Denis; Mathieu Moreau; Maud Combe; Andrew D. Straw; Clément Sire; Guy Theraulaz

doi:10.1371/journal.pone.0339909

Peer Review History

Original SubmissionJuly 4, 2025
4 Jul 2025 Author Response Transfer Alert This paper was transferred from another journal. As a result, its full editorial history (including decision letters, peer reviews and author responses) may not be present. https://doi.org/10.1371/journal.pone.0339909.r001
10 Sep 2025 Decision Letter - Shicheng Li, Editor PONE-D-25-36359A low-cost closed-loop Virtual Reality system to investigate social interactions and collective behavior in fishPLOS ONE Dear Dr. Theraulaz, 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. Please submit your revised manuscript by Oct 25 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. 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If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise. [Note: HTML markup is below. Please do not edit.] 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: Yes Reviewer #2: Yes ******** 2. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes Reviewer #2: Yes ****** 3. 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Reviewer #2: This paper presents a major methodological contribution by developing a low-cost, open-source, closed-loop virtual reality system that allows the study of social interactions in fish with unprecedented control. The results convincingly demonstrate that real fish perceive and follow virtual fish as credible conspecifics, adjusting their speed, depth, and relative position in a flexible and robust manner. The strength of the study lies in its experimental rigor, the quality of the quantitative data, and the full transparency of the shared codes and data. However, the statistical analysis would benefit from including inferential tests to formally support comparisons between conditions. Furthermore, while the system allows for visual closed-loop, the behavior of the virtual fish remains pre-programmed in an open loop in this study, thus limiting the exploration of more complex bidirectional interactions. Finally, although the method is powerful for deciphering individual rules, it does not yet address group dynamics involving multiple real individuals. To significantly strengthen the statistical robustness of the evaluation, several additional analyses are possible. The use of non-parametric Kruskal-Wallis tests, followed by Dunn post-hoc tests, would allow for a formal comparison of the distributions of speed, distance, and depth between the different experimental conditions. In addition, calculating cross-correlations between the speeds and directions of the real and virtual fish would objectively quantify their degree of synchronization and response times. Finally, the addition of a control condition with a non-social stimulus would ensure that the observed behaviors are indeed specific social responses and not simple reactions to a movement. ****** 6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). 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Revision 1
10 Oct 2025 Author Response Responses to Reviewers Reviewers have raised a total of 6 points that we reproduce here in black italicized text. Our answers are given in blue. Response to the comments of Referee 1 This article sounds very interesting and impressive. Written in good English language. #1.1: However, the only flaw that requires major revision and amendment is the related works regarding this study. A: We appreciate the Reviewer’s positive assessment and constructive requests. In the revised version of our paper, we have incorporated additional references (19 to 25) to create a comprehensive and thematically organized Related Work section that more clearly positions our contribution within the existing literature. #1.2: The Result subheading shown the analysis of the experiment followed by discussion. The methodology section needs to be reorganized prior the result and analysis section. A: We have reordered the Methods section before the Results section thus following the PloS One template. #1.3: Conclusion section is not found. Is it replaced with discussion? A: We added a concise conclusion. We hope these revisions make the manuscript clearer, better contextualized, and easier to navigate. Response to the comments of Referee 2 This paper presents a major methodological contribution by developing a low-cost, open-source, closed-loop virtual reality system that allows the study of social interactions in fish with unprecedented control. The results convincingly demonstrate that real fish perceive and follow virtual fish as credible conspecifics, adjusting their speed, depth, and relative position in a flexible and robust manner. The strength of the study lies in its experimental rigor, the quality of the quantitative data, and the full transparency of the shared codes and data. However, the statistical analysis would benefit from including inferential tests to formally support comparisons between conditions. Furthermore, while the system allows for visual closed-loop, the behavior of the virtual fish remains pre-programmed in an open loop in this study, thus limiting the exploration of more complex bidirectional interactions. Finally, although the method is powerful for deciphering individual rules, it does not yet address group dynamics involving multiple real individuals. A: We sincerely thank Reviewer 2 for his/her positive and encouraging assessment of our work. We are pleased that the manuscript was recognized as presenting a major methodological contribution, with rigorous experiments, transparent data sharing, and convincing demonstrations of the ability of real fish to treat virtual fish as credible conspecifics. In the revised manuscript, we have also added a specific measure of the dissimilarity between the PDFs to formally compare behavioral responses across conditions, and the corresponding results are now reported in the Results section. Below we address the two other constructive points raised, and explain how we have revised the manuscript accordingly. Open-loop behavior of the virtual fish. We agree that in the initial submission the virtual fish followed pre-programmed trajectories. Our revised manuscript clarifies that this study aimed to validate the platform in open-loop conditions, while emphasizing that the system is designed for full closed-loop experiments. We now highlight ongoing work in which the trajectory of the virtual fish is controlled in real time by three-dimensional interaction models derived from the computational analysis of real fish pairs. These future experiments will allow bidirectional interactions and causal tests of social rules, which we will report in a separate article. Extension to group dynamics. We acknowledge that the present study also focused on interactions between one real and one virtual fish. The revised version now explicitly outlines how the system will be scaled to project multiple virtual conspecifics that respond dynamically to each other and to the real fish. This will allow tests of how individuals combine information from multiple neighbors and how local rules scale to group-level coordination, directly connecting to predictions from recent modeling work (Lei et al., 2020; Wang et al., 2022; Xue et al., 2023}. #2.1: To significantly strengthen the statistical robustness of the evaluation, several additional analyses are possible. The use of non-parametric Kruskal-Wallis tests, followed by Dunn post-hoc tests, would allow for a formal comparison of the distributions of speed, distance, and depth between the different experimental conditions. A: To address this point, we have now incorporated an additional subsection entitled “Statistical Metric for Probability Distribution Comparison” in the Data Analyses section. In this new analysis, we quantify differences between behavioral distributions observed under distinct experimental conditions using the Hellinger distance, a widely used and robust statistical metric for comparing probability distribution functions. Specifically, given two normalized distributions, the Hellinger distance provides a bounded measure of similarity ranging from 0 (identical distributions) to 1 (non-overlapping distributions). Small values indicate strong similarity, whereas values greater than 0.2 reveal marked differences. This approach allows us to rigorously assess whether variations in fish responses across experimental manipulations (e.g., changes in speed, depth, or distance to the wall of the virtual fish) correspond to statistically meaningful shifts in the underlying behavioral distributions. We also clarify in the revised manuscript how these analyses complement the descriptive statistics already presented, thereby reinforcing the robustness of our findings. By adding this inferential framework, we ensure that our conclusions are not only visually convincing but also formally supported by statistical tests. #2.2: In addition, calculating cross-correlations between the speeds and directions of the real and virtual fish would objectively quantify their degree of synchronization and response times. A: As suggested, we have calculated the cross-temporal correlations between the velocities of the real and virtual objects (a fish or a black sphere) to provide an additional quantification of synchronization and response times. The results fully confirm our previous conclusions. They can be found, together with the figures, in the following parts of the text: - In Sec. 3.8.2, we use the formula (11) to calculate the cross-correlation, where the real fish is taken as the reference of C(\tau). - In Sec. 4.1 and Fig. 6C, showing that the correlation with a virtual conspecific is almost three times larger than with a virtual sphere, showing a clear preference for the social stimulus. - In Sec. 4.2.1 and S2 Fig., we show that in the three cases with different speeds, the values of the correlation remain high, with the real fish anticipating the virtual one at low speed, behaving closely at intermediate values of the speed, and following the virtual fish with a short delay at high speed. - In Sec. 4.3 and S3 Fig., for the case of the two rhodonea, correlations are again high. The real fish follows the virtual one more consistently in Rose 1 than along Rose 2, as the correlation is higher and the delay longer and negative in Rose 1, where the correlation is higher and the delay longer (about 0.23 s, negative), whereas in Rose 2 the delay is almost zero but the correlation is weaker. #2.3: Finally, the addition of a control condition with a non-social stimulus would ensure that the observed behaviors are indeed specific social responses and not simple reactions to a movement. A: We thank the Reviewer for her/his suggestion. We have now included a non-social control stimulus consisting of a black sphere of comparable size to the tested fish. The new results show that fish did not follow or adjust their trajectories relative to the sphere, in sharp contrast to their robust following of virtual conspecifics. This confirms that the observed behaviors are indeed specific to social stimuli and not mere responses to moving objects. The revised manuscript includes these data in the Results section 4.1 (Control condition with a non-social stimulus) and discusses their implications in confirming the social specificity of the responses to 3D avatars. Cited References : Xue, T., Li, X., Lin, G., Escobedo, R., Han, Z., Chen, X., Sire, C. & Theraulaz, G. 2023. Tuning social interactions' strength drives collective response to light intensity in schooling fish. Plos Computational Biology, 19(11):e1011636. Wang, W, Escobedo, R., Sanchez, S., Sire, C., Han, Z. & Theraulaz, G. 2022. The impact of individual perceptual and cognitive factors on collective states in a data-driven fish school model. Plos Computational Biology, 18: e1009437. Lei, L., Escobedo, R., Sire, C., Theraulaz, G. 2020. Computational and robotic modeling reveal parsimonious combinations of interactions between individuals in schooling fish. Plos Computational Biology, 16: e1007194. Attachments Attachment Submitted filename: Rebuttal Letter Sanchez_et_al_R1.pdf https://doi.org/10.1371/journal.pone.0339909.r003
14 Dec 2025 Decision Letter - Shicheng Li, Editor An open-source closed-loop Virtual Reality system to investigate social interactions and collective behavior in fish PONE-D-25-36359R1 Dear Dr. Theraulaz, 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. For questions related to billing, please contact billing support. 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, Shicheng Li Academic Editor PLOS One Additional Editor Comments (optional): Reviewers' comments: https://doi.org/10.1371/journal.pone.0339909.r004
Formally Accepted
Acceptance Letter - Shicheng Li, Editor PONE-D-25-36359R1 PLOS One Dear Dr. Theraulaz, I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS One. Congratulations! Your manuscript is now being handed over to our production team. At this stage, our production department will prepare your paper for publication. This includes ensuring the following: * All references, tables, and figures are properly cited * All relevant supporting information is included in the manuscript submission, * There are no issues that prevent the paper from being properly typeset You will receive further instructions from the production team, including instructions on how to review your proof when it is ready. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few days to review your paper and let you know the next and final steps. Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. 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. You will receive an invoice from PLOS for your publication fee after your manuscript has reached the completed accept phase. If you receive an email requesting payment before acceptance or for any other service, this may be a phishing scheme. Learn how to identify phishing emails and protect your accounts at https://explore.plos.org/phishing. If we can help with anything else, please email us at customercare@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. Shicheng Li Academic Editor PLOS One https://doi.org/10.1371/journal.pone.0339909.r005

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