Traditionally, the Chevreul illusion has been explained in terms of lateral inhibition, which means that brighter areas projected to the retina inhibit the sensitivity of neighbouring retinal areas. The physical luminance cross-section of the midline of the staircase is displayed in the bottom part of the figure. The side of each step adjoining a brighter step seems darker than its other side. The steps adjacent to each other are physically homogeneous however, they seem inhomogeneous (crimped). This does not alter the authors' adherence to all the PLoS ONE policies on sharing data and materials, as detailed online in the guide for authors.įigure 1. There are no patents, products in development or marketed products to declare. through the directorship and 50% ownership of János Geier. through the directorship and 50% ownership of János Geier, who designed the experiments, contributed to the analysis and wrote the paper.Ĭompeting interests: This study was funded by Stereo Vision Ltd. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.įunding: This study was funded by Stereo Vision Ltd. Received: ApAccepted: SeptemPublished: October 13, 2011Ĭopyright: © 2011 Geier, Hudák. PLoS ONE 6(10):Įditor: Steven Barnes, Dalhousie University, Canada We suggest that long range interactions between boundary edges and areas enclosed by them, such that diffusion-based models describe, provide a much more plausible account for these brightness phenomena, and local models are insufficient.Ĭitation: Geier J, Hudák M (2011) Changing the Chevreul Illusion by a Background Luminance Ramp: Lateral Inhibition Fails at Its Traditional Stronghold - A Psychophysical Refutation. Area ratios seem insignificant the role of boundary edges seems crucial. Since all conditions of the lateral inhibition account were untouched within the staircase, lateral inhibition fails to model these perceptual changes. The result is that though the inner ramp is rather narrow (mean = 0.51 deg, SD = 0.48 deg, N = 23), it still dominates perception.
To see whether the change of the entire background area or that of the staircase boundary edges were more important, we placed another ramp around the staircase, whose direction was opposite to that of the original, larger ramp. When the background of the staircase was uniform, 14 saw the illusion, and 9 saw no illusion. In our psychophysical experiments, all 23 observers reported a strong illusion, when the direction of the ramp was identical to that of the staircase, and all reported homogeneous steps (no illusion) when its direction was the opposite.
For this aim, we placed the Chevreul staircase in a luminance ramp background, which noticeably changed the illusion. Here we prove that lateral inhibition is insufficient to explain the Chevreul illusion. One of the last strongholds of lateral inhibition is the Chevreul illusion, which is often illustrated even in current textbooks. Lateral inhibition has been considered the foundation-stone of early vision for a century, upon which several computational models of brightness perception are built. It is generally explained by lateral inhibition, according to which brighter areas projected to the retina inhibit the sensitivity of neighbouring retinal areas. The Chevreul illusion is a well-known 19 th century brightness illusion, comprising adjacent homogeneous grey bands of different luminance, which are perceived as inhomogeneous.