SNARC-like compatibility effects for physical and phenomenal magnitudes: a study on visual illusions

  • Valter PrpicEmail author
  • Alessandro Soranzo
  • Ilaria Santoro
  • Carlo Fantoni
  • Alessandra Galmonte
  • Tiziano Agostini
  • Mauro Murgia
Original Article


Both numerical and non-numerical magnitudes elicit similar Spatial-Numerical Association of Response Codes (SNARC) effects, with small magnitudes associated with left hand responses and large magnitudes associated with right hand responses (Dehaene et al., J Exp Psychol Gen 122(3), 371, 1993). In the present study, we investigated whether the phenomenal size of visual illusions elicits the same SNARC-like effect revealed for the physical size of pictorial surfaces. Four experiments were conducted by using the Delboeuf illusion (Experiment 1) and the Kanizsa triangle illusion (Experiments 2, 3 and 4). Experiment 1 suggests the presence of a SNARC-like compatibility effect for the physical size of the inducers, while this effect was not revealed for the phenomenal size of the induced elements, possibly masked by a stronger effect of the inducers. A SNARC-like effect for the phenomenal size of the Kanizsa triangle was revealed when participants directly compared the size of the triangles (Experiment 4). Conversely, when participants performed an indirect task (orientation judgment), the SNARC-like effect was present neither for the illusory nor for the physical displays (Experiments 2 and 3). The effect revealed for the size of illusory triangles was comparable to that of real triangles with physical contours, suggesting that both phenomenal and physical magnitudes similarly elicit SNARC-like effects.



A special thanks goes to Mattia Sarcetta, Katie Elliot, Stefania Caporal and Fulvio Bullo for recruiting participants for this study. We also thank Michele Stefanuto and Francesco Sinicco for their help on stimuli creation, and Courtney Goodridge for the English proofreading. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Compliance with ethical standards

Conflict of interest

The authors declare no conflict of interest.

Ethical standards

The present study was approved by the Research Ethics Committee of the University of Trieste in compliance with national legislation, the Ethical Code of the Italian Association of Psychology, and the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Institue for Psychological Science, Faculty of Health and Life SciencesDe Montfort UniversityLeicesterUK
  2. 2.Department of Psychology, Sociology and PoliticsSheffield Hallam UniversitySheffieldUK
  3. 3.Department of Life SciencesUniversity of TriesteTriesteItaly
  4. 4.Department of Medical, Surgical and Health SciencesUniversity of TriesteTriesteItaly

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