Why some size illusions affect grip aperture

Jeroen B.J. Smeets*, Erik Kleijn, Marlijn van der Meijden, Eli Brenner

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


There is extensive literature debating whether perceived size is used to guide grasping. A possible reason for not using judged size is that using judged positions might lead to more precise movements. As this argument does not hold for small objects and all studies showing an effect of the Ebbinghaus illusion on grasping used small objects, we hypothesized that size information is used for small objects but not for large ones. Using a modified diagonal illusion, we obtained an effect of about 10% on perceptual judgements, without an effect on grasping, irrespective of object size. We therefore reject our precision hypothesis. We discuss the results in the framework of grasping as moving digits to positions on an object. We conclude that the reported disagreement on the effect of illusions is because the Ebbinghaus illusion not only affects size, but—unlike most size illusions—also affects perceived positions.

Original languageEnglish
Pages (from-to)969-979
Number of pages11
JournalExperimental Brain Research
Issue number4
Early online date17 Mar 2020
Publication statusPublished - Apr 2020


  • Grasping
  • Inconsistency
  • Prehension
  • Visual illusion
  • Weber’s law


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