{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T18:24:15Z","timestamp":1787077455555,"version":"build-2736575974"},"reference-count":30,"publisher":"Public Library of Science (PLoS)","issue":"8","license":[{"start":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T00:00:00Z","timestamp":1787011200000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100017090","name":"Sony","doi-asserted-by":"publisher","id":[{"id":"10.13039\/100017090","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS One"],"abstract":"<jats:p>Robots designed for therapy and social interaction are often intended to evoke a sense of \u201canimacy\u201d in humans. While many robots have been developed to imitate life-like appearance and joint movements, relatively little attention has been given to the effect of whole-body expansion and contraction\u2014volume-changing movements commonly observed in living organisms\u2014on perceived animacy. In this study, we developed MOFU (MOrphing Fluffy Unit), a mobile robot capable of whole-body expansion and contraction using a single motor enclosed within a fluffy exterior. MOFU employs a \u201cJitterbug\u201d structure, a geometric transformation mechanism that enables smooth volume changes using a single actuator, with the robot height varying from approximately 210 mm to 280 mm. Additionally, it is equipped with a differential two-wheel drive mechanism for locomotion. We conducted an online survey using videos of MOFU\u2019s behavior to evaluate the effect of expansion\u2013contraction movements on animacy perception. Participants rated their impressions using the Godspeed Questionnaire Series. First, we compared participants\u2019 ratings across videos of MOFU in stationary states, with and without expansion\u2013contraction, and separately, with and without rotational motion. Both the expansion\u2013contraction and rotational movements independently increased perceived animacy. Second, we hypothesized that presenting two MOFUs simultaneously would enhance perceived animacy further; however, this prediction was not supported, as no significant difference was observed. Exploratory analyses were also performed across the four dual-robot motion conditions. Third, when rotational and expansion\u2013contraction motions were combined with locomotion, animacy ratings were higher than for locomotion alone. These results suggest that volume-changing movements, such as expansion and contraction, enhance the perception of animacy in robots. Consequently, incorporating physical volume change may be an important design element in the development of future robots aimed at shaping human impressions.<\/jats:p>","DOI":"10.1371\/journal.pone.0354179","type":"journal-article","created":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T17:24:30Z","timestamp":1787073870000},"page":"e0354179","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":0,"title":["MOFU: Development of a MOrphing Fluffy Unit with expansion and contraction capabilities and evaluation of the animacy of its movements"],"prefix":"10.1371","volume":"21","author":[{"given":"Taisei","family":"Mogi","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mari","family":"Saito","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2102-9358","authenticated-orcid":true,"given":"Yoshihiro","family":"Nakata","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"340","published-online":{"date-parts":[[2026,8,18]]},"reference":[{"issue":"8","key":"pone.0354179.ref001","doi-asserted-by":"crossref","first-page":"2527","DOI":"10.1109\/JPROC.2012.2200559","article-title":"Therapeutic Seal Robot as Biofeedback Medical Device: Qualitative and Quantitative Evaluations of Robot Therapy in Dementia Care","volume":"100","author":"T Shibata","year":"2012","journal-title":"Proc IEEE"},{"key":"pone.0354179.ref002","doi-asserted-by":"crossref","unstructured":"Jeong S, Breazeal C, Logan D, Weinstock P. 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Face on a globe: A spherical robot that appears lifelike through smooth deformations and autonomous movement. In: 2022 17th ACM\/IEEE International Conference on Human-Robot Interaction (HRI). IEEE; 2022. p. 502\u201310.","DOI":"10.1109\/HRI53351.2022.9889453"},{"key":"pone.0354179.ref010","doi-asserted-by":"crossref","unstructured":"Fujita H, Komatsu T, Fraune MR, Tsui KM. Touch from Robots Loses to Chatting via Text: A Comparative Study of Sympathy Demonstrated Using Text, Robot Arm, and Qoobo. In: Companion of the 2024 ACM\/IEEE International Conference on Human-Robot Interaction. HRI \u201924. New York (NY): Association for Computing Machinery; 2024. p. 473\u20137.","DOI":"10.1145\/3610978.3640730"},{"key":"pone.0354179.ref011","doi-asserted-by":"crossref","unstructured":"Fernaeus Y, H\u00e5kansson M, Jacobsson M, Ljungblad S. How do you play with a robotic toy animal?: a long-term study of Pleo. In: Proceedings of the 9th International Conference on Interaction Design and Children. IDC \u201910. New York (NY): Association for Computing Machinery; 2010. p. 39\u201348.","DOI":"10.1145\/1810543.1810549"},{"key":"pone.0354179.ref012","unstructured":"Tombot, Inc. Robotic Emotional Support Animals; n.d. Available from: https:\/\/tombot.com"},{"key":"pone.0354179.ref013","unstructured":"Takeda Y, Miyake T, Uto H, Yoshiike Y, De Silva RR, Okada M. COLUMN: A Novel Architecture for Transformable Artifact. In: Proceedings of VRIC 2010. Laval, France. 2010. p. 271\u20137. Available from: https:\/\/cir.nii.ac.jp\/crid\/1574231874030670592"},{"key":"pone.0354179.ref014","doi-asserted-by":"crossref","unstructured":"Hedayati H, Suzuki R, Leithinger D, Szafir D. PufferBot: Actuated Expandable Structures for Aerial Robots. In: 2020 IEEE\/RSJ International Conference on Intelligent Robots and Systems (IROS). 2020. p. 1338\u20131343.","DOI":"10.1109\/IROS45743.2020.9341088"},{"key":"pone.0354179.ref015","doi-asserted-by":"crossref","unstructured":"Matheus K, Vazquez M, Scassellati B. A social robot for anxiety reduction via deep breathing. In: 2022 31st IEEE International Conference on Robot and Human Interactive Communication (RO-MAN). IEEE; 2022. p. 89\u201394.","DOI":"10.1109\/RO-MAN53752.2022.9900638"},{"issue":"2","key":"pone.0354179.ref016","doi-asserted-by":"crossref","first-page":"553","DOI":"10.3758\/s13414-017-1439-x","article-title":"Different contexts change the impression of animacy","volume":"80","author":"G Parovel","year":"2018","journal-title":"Atten Percept Psychophys"},{"issue":"11","key":"pone.0354179.ref017","doi-asserted-by":"crossref","DOI":"10.1371\/journal.pone.0240622","article-title":"Two is better than one: Social rewards from two agents enhance offline improvements in motor skills more than single agent","volume":"15","author":"M Shiomi","year":"2020","journal-title":"PLoS One"},{"issue":"2","key":"pone.0354179.ref018","doi-asserted-by":"crossref","DOI":"10.1371\/journal.pone.0281604","article-title":"Two is better than one: Apologies from two robots are preferred","volume":"18","author":"Y Okada","year":"2023","journal-title":"PLoS One"},{"issue":"1","key":"pone.0354179.ref019","doi-asserted-by":"crossref","first-page":"23","DOI":"10.5057\/jjske.TJSKE-D-18-00037","article-title":"Importance of Soft Tactility on Robot-Assisted Therapy","volume":"18","author":"R Hayashi","year":"2019","journal-title":"Trans Jpn Soc Kansei Eng"},{"issue":"11","key":"pone.0354179.ref020","doi-asserted-by":"crossref","first-page":"1829","DOI":"10.1007\/s12369-023-00975-5","article-title":"(Hu)man-Like Robots: The Impact of Anthropomorphism and Language on Perceived Robot Gender","volume":"15","author":"E Roesler","year":"2023","journal-title":"Int J Soc Robot"},{"issue":"2","key":"pone.0354179.ref021","doi-asserted-by":"crossref","first-page":"528","DOI":"10.1109\/LRA.2022.3227872","article-title":"Flipper-Style Locomotion Through Strong Expanding Modular Robots","volume":"8","author":"L Chin","year":"2023","journal-title":"IEEE Robot Autom Lett"},{"key":"pone.0354179.ref022","doi-asserted-by":"crossref","unstructured":"Lipton J, Chin L, Miske J, Rus D. Modular Volumetric Actuators Using Motorized Auxetics. In: 2019 IEEE\/RSJ International Conference on Intelligent Robots and Systems (IROS). IEEE; 2019. p. 7460\u20137466.","DOI":"10.1109\/IROS40897.2019.8968187"},{"key":"pone.0354179.ref023","doi-asserted-by":"crossref","first-page":"203","DOI":"10.1016\/0898-1221(89)90160-0","article-title":"The complete set of Jitterbug transformers and the analysis of their motion","volume":"17","author":"HF Verheyen","year":"1989","journal-title":"Comput Math Appl"},{"issue":"6","key":"pone.0354179.ref024","doi-asserted-by":"crossref","first-page":"2280","DOI":"10.1016\/j.patcog.2014.01.005","article-title":"Automatic generation and detection of highly reliable fiducial markers under occlusion","volume":"47","author":"S Garrido-Jurado","year":"2014","journal-title":"Pattern Recognit"},{"issue":"2","key":"pone.0354179.ref025","doi-asserted-by":"crossref","first-page":"175","DOI":"10.3758\/BF03193146","article-title":"G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences","volume":"39","author":"F Faul","year":"2007","journal-title":"Behav Res Methods"},{"issue":"1","key":"pone.0354179.ref026","doi-asserted-by":"crossref","first-page":"71","DOI":"10.1007\/s12369-008-0001-3","article-title":"Measurement instruments for the anthropomorphism, animacy, likeability, perceived intelligence, and perceived safety of robots","volume":"1","author":"C Bartneck","year":"2009","journal-title":"Int J Soc Robot"},{"key":"pone.0354179.ref027","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1007\/978-3-030-89738-3_24-1","article-title":"Godspeed Questionnaire Series: Translations and Usage.","volume-title":"International Handbook of Behavioral Health Assessment","author":"C. Bartneck","year":"2023"},{"issue":"2","key":"pone.0354179.ref028","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1145\/3772066","article-title":"Choosing the \u201cPerfect\u201d Scale: A Primer to Evaluate Existing Scales in HRI","volume":"15","author":"L Saad","year":"2026","journal-title":"J Hum-Robot Interact"},{"issue":"6","key":"pone.0354179.ref029","doi-asserted-by":"crossref","first-page":"1508","DOI":"10.1016\/j.chb.2010.05.015","article-title":"Revisiting the uncanny valley theory: Developing and validating an alternative to the Godspeed indices","volume":"26","author":"CC Ho","year":"2010","journal-title":"Comput Hum Behav"},{"key":"pone.0354179.ref030","doi-asserted-by":"crossref","unstructured":"Carpinella CM, Wyman AB, Perez MA, Stroessner SJ. The Robotic Social Attributes Scale (RoSAS): Development and Validation. In: Proceedings of the 2017 ACM\/IEEE International Conference on Human-Robot Interaction. HRI \u201917. 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