title: Perceptual similarity and the neural correlates of geometrical illusions in human brain structure.
abstract: Geometrical visual illusions are an intriguing phenomenon, in which subjective perception consistently misjudges the objective, physical properties of the visual stimulus. Prominent theoretical proposals have been advanced attempting to find common mechanisms across illusions. But empirically testing the similarity between illusions has been notoriously difficult because illusions have very different visual appearances. Here we overcome this difficulty by capitalizing on the variability of the illusory magnitude across participants. Fifty-nine healthy volunteers participated in the study that included measurement of individual illusion magnitude and structural MRI scanning. We tested the Muller-Lyer, Ebbinghaus, Ponzo, and vertical-horizontal geometrical illusions as well as a non-geometrical, contrast illusion. We found some degree of similarity in behavioral judgments of all tested geometrical illusions, but not between geometrical illusions and non-geometrical, contrast illusion. The highest similarity was found between Ebbinghaus and Muller-Lyer geometrical illusions. Furthermore, the magnitude of all geometrical illusions, and particularly the Ebbinghaus and Muller-Lyer illusions, correlated with local gray matter density in the parahippocampal cortex, but not in other brain areas. Our findings suggest that visuospatial integration and scene construction processes might partly mediate individual differences in geometric illusory perception. Overall, these findings contribute to a better understanding of the mechanisms behind geometrical illusions.
authors.affiliation: Inserm U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, F-75013, Paris, France.|Institute of Cognitive Neuroscience, University College London, London, UK.
authors.forename: Vadim
authors.initials: V
authors.lastname: Axelrod
authors.affiliation: Institute of Cognitive Neuroscience, University College London, London, UK.|Experimental Psychology, University College London, London, UK.
authors.forename: D Samuel
authors.initials: DS
authors.lastname: Schwarzkopf
authors.affiliation: Institute of Cognitive Neuroscience, University College London, London, UK.|Visual Science and Optometry, Bar Ilan University, Ramat Gan, Israel.
authors.forename: Sharon
authors.initials: S
authors.lastname: Gilaie-Dotan
authors.affiliation: Institute of Cognitive Neuroscience, University College London, London, UK.|Wellcome Trust Centre for Neuroimaging, University College London, London, UK.
authors.forename: Geraint
authors.initials: G
authors.lastname: Rees
mesh_terms: D000328:Adult; D001921:Brain / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007600:Judgment; D008279:Magnetic Resonance Imaging; D008297:Male; D010364:Pattern Recognition, Visual; D010775:Photic Stimulation; D025341:Principal Component Analysis; D012858:Size Perception