{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,1]],"date-time":"2026-05-01T12:47:04Z","timestamp":1777639624805,"version":"3.51.4"},"reference-count":67,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2022,4,4]],"date-time":"2022-04-04T00:00:00Z","timestamp":1649030400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Teaching is an activity that requires understanding the class\u2019s reaction to evaluate the teaching methodology effectiveness. This operation can be easy to achieve in small classrooms, while it may be challenging to do in classes of 50 or more students. This paper proposes a novel Internet of Things (IoT) system to aid teachers in their work based on the redundant use of non-invasive techniques such as facial expression recognition and physiological data analysis. Facial expression recognition is performed using a Convolutional Neural Network (CNN), while physiological data are obtained via Photoplethysmography (PPG). By recurring to Russel\u2019s model, we grouped the most important Ekman\u2019s facial expressions recognized by CNN into active and passive. Then, operations such as thresholding and windowing were performed to make it possible to compare and analyze the results from both sources. Using a window size of 100 samples, both sources have detected a level of attention of about 55.5% for the in-presence lectures tests. By comparing results coming from in-presence and pre-recorded remote lectures, it is possible to note that, thanks to validation with physiological data, facial expressions alone seem useful in determining students\u2019 level of attention for in-presence lectures.<\/jats:p>","DOI":"10.3390\/s22072773","type":"journal-article","created":{"date-parts":[[2022,4,4]],"date-time":"2022-04-04T09:49:41Z","timestamp":1649065781000},"page":"2773","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["A Novel Redundant Validation IoT System for Affective Learning Based on Facial Expressions and Biological Signals"],"prefix":"10.3390","volume":"22","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-4843-1267","authenticated-orcid":false,"given":"Antonio Costantino","family":"Marceddu","sequence":"first","affiliation":[{"name":"Department of Control and Computer Engineering, Politecnico di Torino, 10129 Turin, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1247-4230","authenticated-orcid":false,"given":"Luigi","family":"Pugliese","sequence":"additional","affiliation":[{"name":"Department of Control and Computer Engineering, Politecnico di Torino, 10129 Turin, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2163-9925","authenticated-orcid":false,"given":"Jacopo","family":"Sini","sequence":"additional","affiliation":[{"name":"Department of Control and Computer Engineering, Politecnico di Torino, 10129 Turin, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8607-593X","authenticated-orcid":false,"given":"Gustavo Ramirez","family":"Espinosa","sequence":"additional","affiliation":[{"name":"Department of Control and Computer Engineering, Politecnico di Torino, 10129 Turin, Italy"},{"name":"Electronics Department, Engineering School, Pontificia Universidad Javeriana, Bogota 1301, Colombia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3430-9706","authenticated-orcid":false,"given":"Mohammadreza","family":"Amel Solouki","sequence":"additional","affiliation":[{"name":"Department of Control and Computer Engineering, Politecnico di Torino, 10129 Turin, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3907-5934","authenticated-orcid":false,"given":"Pietro","family":"Chiavassa","sequence":"additional","affiliation":[{"name":"Department of Control and Computer Engineering, Politecnico di Torino, 10129 Turin, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8371-6685","authenticated-orcid":false,"given":"Edoardo","family":"Giusto","sequence":"additional","affiliation":[{"name":"Department of Control and Computer Engineering, Politecnico di Torino, 10129 Turin, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0065-8614","authenticated-orcid":false,"given":"Bartolomeo","family":"Montrucchio","sequence":"additional","affiliation":[{"name":"Department of Control and Computer Engineering, Politecnico di Torino, 10129 Turin, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5821-3418","authenticated-orcid":false,"given":"Massimo","family":"Violante","sequence":"additional","affiliation":[{"name":"Department of Control and Computer Engineering, Politecnico di Torino, 10129 Turin, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8772-4105","authenticated-orcid":false,"given":"Francesco","family":"De Pace","sequence":"additional","affiliation":[{"name":"Institute of Visual Computing and Human-Centered Technology, Vienna University of Technology (TU Wien), 1040 Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,4,4]]},"reference":[{"key":"ref_1","unstructured":"Caine, R.N., and Caine, G. 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