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Zahide Pamir, Huseyin Boyacı; Context-dependent Brightness Affects Perceived Contrast at Threshold and Suprathreshold Levels. Journal of Vision 2016;16(12):821. doi: 10.1167/16.12.821.
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© ARVO (1962-2015); The Authors (2016-present)
Contrast is an important feature for performance on many visual tasks such as object identification, speed or motion detection (Kilpeläinen, Nurminen, & Donner, 2011). Perceived contrast of a grating depends on the luminance of its background. On the other hand, context often causes a large difference between luminance and its perceptual counterpart, brightness (e.g. simultaneous brightness contrast). Thus, characterizing different effects of luminance- and context-dependent brightness on contrast is critical. In this study we investigate how context-dependent brightness affects contrast judgements using a variant of Adelson's checkerboard illusion stimulus (Adelson, 1995). Two series of behavioral experiments were conducted. In the first series, we measured the perceived contrast of gratings using several different implementations of a method of adjustment paradigm. Participants reported the contrast of rectified gratings with incremental and decremental suprathreshold contrasts superimposed on equiluminant target regions, for various levels of frequency, background luminance and brightness, and photometric contrast. Results show that gratings superimposed on equiluminant but perceptually brighter target regions were perceived to have higher contrast than those superimposed on perceptually darker target regions (N=6). However, this pattern was only valid for incremental contrast, not for decremental contrast. In the second series of experiments, we measured the contrast detection thresholds using a 2-IFC procedure. We found that detection threshold is lower for the gratings superimposed on equiluminant but perceptually brighter target regions (N=6). Our results show that context-dependent brightness of the target region, not only its luminance, influences the perceived contrast of gratings both at threshold and suprathreshold levels. These findings unveil the significant effect of context-dependent brightness on contrast perception, thereby provide evidence that contrast perception does not depend only on the photometric quantities of the image formed on the retina, and that context-dependent factors also play a role.
Meeting abstract presented at VSS 2016
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