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Marianne Maertens, Felix A. Wichmann; On the relationship between luminanc increment thresholds and apparent brightness. Journal of Vision 2010;10(7):424. doi: 10.1167/10.7.424.
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It has long been known that the just noticeable difference (JND) between two stimulus intensities increases proportional to the background intensity - Weber's law. It is less clear, however, whether the JND is a function of the physical or apparent stimulus intensity. In many situations, especially in the laboratory using simple stimuli such as uniform patches or sinusoidal gratings, physical and perceived intensity coincide. Reports that tried to disentangle the two factors yielded inconsistent results (e.g. Heinemann, 1961 Journal of Experimental Psychology 61 389-399; Cornsweet and Teller, 1965 Journal of the Optical Society of America 55(10) 1303-1308; Henning, Millar and Hill, 2000 Journal of the Optical Society of America 17(7) 1147-1159; Hillis and Brainard, 2007 Current Biology 17 1714-1719). A necessary condition for estimating the potential effect of appearance on JNDs is to quantify the difference between physical and apparent intensity in units of physical intensity, because only that will allow to predict the expected JNDs. In the present experiments we utilized a version of the Craik-O'Brien-Cornsweet stimulus (Purves, Shimpi and Lotto, 1999 Journal of Neuroscience 19 8542-8551) to study the relationship between JNDs and apparent brightness. We quantitatively assessed apparent brightness using a paired comparison procedure related to maximum-likelihood difference scaling (Maloney and Yang, 2003 Journal of Vision 3(8) 573-585), in which observers compared the perceptual difference between two pairs of surface intensities. Using the exact same stimulus arrangement, that is, two pairs of surfaces, we asked observers to detect a luminance increment in a standard spatial 4-alternative forced-choice (4-AFC) task.
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