{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,3,10]],"date-time":"2025-03-10T09:40:18Z","timestamp":1741599618370,"version":"3.38.0"},"reference-count":56,"publisher":"PeerJ","license":[{"start":{"date-parts":[[2025,3,10]],"date-time":"2025-03-10T00:00:00Z","timestamp":1741564800000},"content-version":"unspecified","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"The Austrian Science Fund (FWF) through an ESPRIT grant","award":["10.55776\/ESP433"],"award-info":[{"award-number":["10.55776\/ESP433"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"abstract":"<jats:p>Understanding cognitive and neural mechanisms underlying quantity processing is crucial for unraveling human cognition. The existence of a single magnitude system, encompassing non-symbolic number estimation alongside other magnitudes like time and space, is still highly debated since clear evidence is limited. Recent research examined whether spatial biases also influence numerosity judgments, using visual illusions like the Delboeuf illusion. While findings support a generalized magnitude system, direct comparisons of spatial and numerical Delboeuf illusions are missing. This study explored whether perceptual biases similarly affect different magnitude processing and whether transcranial alternating current stimulation (tACS) modulates these processes. Participants underwent three tACS conditions (seven Hz, 18 Hz, placebo) while performing tasks involving the classic and numerical Delboeuf illusions. We hypothesized that theta-frequency tACS (seven Hz) would enhance visual integration and illusion strength, while beta tACS (18 Hz) would reduce it by promoting visual segregation. Results indicated higher discrimination accuracy in area-based tasks than numerical judgments. Nonetheless, a significant correlation between performances in spatial and numerical illusions supported the existence of a shared mechanism for magnitude processing. Contrary to expectations, seven Hz tACS reduced the perceptual illusion\u2019s strength. No significant interaction emerged between tACS frequency and discrimination abilities. These findings deepen our understanding of the cognitive processes involved in magnitude perception, potentially supporting the hypothesis of a generalized magnitude system. They also highlight the potential and limitations of non-invasive brain stimulation techniques, such as tACS, in modulating perceptual processes, offering insights into the neural underpinnings of quantity perception.<\/jats:p>","DOI":"10.7717\/peerj.19064","type":"journal-article","created":{"date-parts":[[2025,3,10]],"date-time":"2025-03-10T08:34:52Z","timestamp":1741595692000},"page":"e19064","source":"Crossref","is-referenced-by-count":0,"title":["Exploring the classical and numerical Delboeuf illusion: the impact of transcranial alternating current stimulation on magnitude processing"],"prefix":"10.7717","volume":"13","author":[{"given":"Maria","family":"Santac\u00e0","sequence":"first","affiliation":[{"name":"Department of Behavioural and Cognitive Biology, University of Vienna, Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Francesco","family":"Carabba","sequence":"additional","affiliation":[{"name":"Department of General Psychology, University of Padua, Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Achini Mihindukulasooriya","family":"Fernando","sequence":"additional","affiliation":[{"name":"Department of General Psychology, University of Padua, Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Enrico","family":"Pitocco","sequence":"additional","affiliation":[{"name":"Department of General Psychology, University of Padua, Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Luca","family":"Battaglini","sequence":"additional","affiliation":[{"name":"Department of General Psychology, University of Padua, Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Umberto","family":"Granziol","sequence":"additional","affiliation":[{"name":"Department of General Psychology, University of Padua, Padua, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"4443","published-online":{"date-parts":[[2025,3,10]]},"reference":[{"issue":"1","key":"10.7717\/peerj.19064\/ref-1","doi-asserted-by":"publisher","first-page":"123","DOI":"10.3758\/s13423-021-01979-w","article-title":"Number is not just an illusion: discrete numerosity is encoded independently from perceived size","volume":"29","author":"Adriano","year":"2022","journal-title":"Psychonomic Bulletin & Review"},{"issue":"1","key":"10.7717\/peerj.19064\/ref-2","doi-asserted-by":"publisher","first-page":"13571","DOI":"10.1038\/s41598-018-31893-6","article-title":"Independent adaptation mechanisms for numerosity and size perception provide evidence against a common sense of magnitude","volume":"8","author":"Anobile","year":"2018","journal-title":"Scientific Reports"},{"issue":"9","key":"10.7717\/peerj.19064\/ref-3","doi-asserted-by":"publisher","first-page":"1774","DOI":"10.1016\/j.clinph.2017.06.001","article-title":"Low intensity transcranial electric stimulation: safety, ethical, legal regulatory and application guidelines","volume":"128","author":"Antal","year":"2017","journal-title":"Clinical Neurophysiology"},{"key":"10.7717\/peerj.19064\/ref-4","article-title":"Fitting linear mixed-effects models using the lme4 package in R","author":"Bates","year":"2008"},{"key":"10.7717\/peerj.19064\/ref-5","doi-asserted-by":"publisher","first-page":"116451","DOI":"10.1016\/j.neuroimage.2019.116451","article-title":"Parietal tACS at beta frequency improves vision in a crowding regime","volume":"208","author":"Battaglini","year":"2020","journal-title":"NeuroImage"},{"issue":"1","key":"10.7717\/peerj.19064\/ref-6","doi-asserted-by":"publisher","first-page":"289","DOI":"10.1111\/j.2517-6161.1995.tb02031.x","article-title":"Controlling the false discovery rate: a practical and powerful approach to multiple testing","volume":"57","author":"Benjamini","year":"1995","journal-title":"Journal of the Royal Statistical Society Series B: Statistical Methodology"},{"issue":"7247","key":"10.7717\/peerj.19064\/ref-7","doi-asserted-by":"publisher","first-page":"1468","DOI":"10.1136\/bmj.320.7247.1468","article-title":"Statistics Notes: the odds ratio","volume":"320","author":"Bland","year":"2000","journal-title":"BMJ"},{"issue":"6","key":"10.7717\/peerj.19064\/ref-8","doi-asserted-by":"publisher","first-page":"425","DOI":"10.1016\/j.cub.2008.02.052","article-title":"A visual sense of number","volume":"18","author":"Burr","year":"2008","journal-title":"Current Biology"},{"issue":"5","key":"10.7717\/peerj.19064\/ref-9","doi-asserted-by":"publisher","first-page":"986","DOI":"10.1162\/jocn_a_00546","article-title":"Commonalities for numerical and continuous quantity skills at temporo-parietal junction","volume":"26","author":"Cappelletti","year":"2014","journal-title":"Journal of Cognitive Neuroscience"},{"issue":"4","key":"10.7717\/peerj.19064\/ref-10","doi-asserted-by":"publisher","first-page":"860","DOI":"10.1080\/03610911003650383","article-title":"How big is a big odds ratio? 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