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Suncica Zdravkovic; The influence of object identity on lightness constancy. Journal of Vision 2008;8(6):566. doi: 10.1167/8.6.566.
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© ARVO (1962-2015); The Authors (2016-present)
Lightness constancy refers to the visual system's ability to detect the same grey shade regardless of current light intensity. A typical paradigm involves the comparison of two objects of the same shade placed under different illumination levels. Some failure in constancy is usually observed. In an attempt to stress object identity, we have recently developed a novel paradigm in which a lightness match is taken in one illumination and then the target is relocated to another illumination for the second match. Even here, there is still failure in constancy. In a previous study (Zdravkovic, 2006), one grey shade was used for the first match and a different grey shade was used for the second match; observers were essentially tricked into thinking that only a single object was presented. The second match varied as a function of the shade of the first target. That is, observers misperceived the second shade, making a match in the direction of the first shade. Rather than simply demonstrating constancy failure, these results illustrated how the strength of constancy could be measured. Using the same paradigm, two new studies were designed to investigate the relevance of context on the strength of constancy: illumination in the first experiment and background in the second. These two manipulations were expected to produce opposite results. Reduction of the illumination difference between the two target levels should increase constancy, while a decrease in background articulation should decrease constancy. In the first experiment the illumination difference was reduced (from 1:13 in our original experiments to 1:2.) and there was no failure in constancy. In the second experiment articulation of the background was reduced. In all previous experiments the back wall was covered with different grey shades, here it was plain black. As expected, there was significant failure in constancy.
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