Extending the watercolour illusion: differential effects of real colours versus afterimage colours S Hazenberg, R van Lier |
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Donders Institute, Radboud University Nijmegen, Netherlands
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| We investigated filling-in of coloured afterimages [Van Lier et al., 2009, Current Biology 19(8), R323–R324 ] and compared them with filling-in of real colours in the watercolour illusion [Pinna et al., 2001, Vision Research 41, 2669–2676]. We used shapes comprising two thin adjacent undulating outlines of which the inner or the outer outline was chromatic, while the other was achromatic. The outlines could be presented simultaneously, inducing the watercolour effect, or in an alternating fashion, inducing coloured afterimages of the chromatic outlines. In Experiment 1, using only alternating outlines, these afterimages triggered filling-in, revealing an ‘afterimage watercolour’ effect. Depending on whether the inner or the outer outline was chromatic, filling-in of a negative or a positive afterimage colour was perceived. In Experiment 2, simultaneous and alternating presentations were compared. During simultaneous presentation, filling-in induced by the inner chromatic outline was strongest. In contrast, during alternating presentation, the strength of filling-in induced by the outer chromatic contour appeared to be strongest. Comparisons with Experiment 1 showed that, while afterimage filling-in induced by the inner contour depended on the luminance contrast between the interior of the shape and that outline, afterimage filling-in induced by the outer contour appeared more robust. |
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