Abstract
The filled-unfilled space illusion was investigated as a possible explanation for the asymmetry (difference in strength) between tails-out and tails-in versions of the Müller -Lyer illusion. Previous work has shown that removal of the horizontal shaft makes both configurations look shorter, but affects them unequally and only partially reduces the asymmetry. In two experiments, illusion strength was varied by use of either different tail lengths or single- vs. double-ended figures. Subjects used method of adjustment with stimuli presented by computer. When the Müller -Lyer was sufficiently weak, shaft removal had equal effects on both tails-in and tails-out configurations, but less effect on plain lines. This produced a reversal of the usual asymmetry, that is, tails-in was stronger than tails-out. It is concluded that the asymmetry is caused by the filled-unfilled illusion. This may require reassessment of the view that the two Müller -Lyer versions are different illusions.
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Beagley, W.K. Interaction space of Müller-Lyer with filled-unfilled illusion: An explanation of Müller-Lyer asymmetry. Perception & Psychophysics 37, 45–49 (1985). https://doi.org/10.3758/BF03207137
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DOI: https://doi.org/10.3758/BF03207137