In addition, the finding of Economou et al. (
2007) that lightness matches were identical for equiluminant incremental target patches placed on variable surrounds is itself controversial. Economou et al. (
2007) cite eight studies that, in their view, also failed to find differential simultaneous brightness/lightness contrast effects for incremental targets (Agostini & Bruno,
1996; Arend & Spehar,
1993b; Diamond,
1953; Gilchrist,
1988; Heinemann,
1955; Jacobsen & Gilchrist,
1988; Kozaki,
1963,
1965). However, a careful examination of these studies reveals that this conclusion may not be justified. For example, in Heinemann's experiment (
1955, Figure 3;
1972, Figure 2), a matching patch (which he called a comparison patch) on a dark surround was adjusted to match a target patch (which he called a test patch) as a function of target (test) patch inducing surround. Within the range where the target (test) patches were increments relative to their inducing surrounds, Heinemann found, at first, a slight but consistent increase in the brightness of the target (test) patches, followed by a depression in target (test) patch brightness that became precipitous as the luminance of the target (test) patch approached that of the inducing surround. It seems inaccurate, therefore, to cite Heinemann's work as evidence for no effect of inducing surround on the brightness of target (test) patches that are increments. Arend and Spehar (
1993b) also found a differential effect of surround luminance on matching (test) patch brightness/lightness judgments for target (standard) patch increments. Interestingly, they found that the magnitude of this differential effect depended on the particular stimulus conditions in the far surround of the stimulus (see their Figures 3 and 8). The effect was quite small and, in agreement with Economou et al. (
2007), appeared absent for one of the three subjects for matching (test) patch increments on variable surrounds placed on Mondrian backgrounds of fixed luminance. The effect, however, was very apparent for uniform outer backgrounds that were the same luminance (i.e., that co-varied with) the inner surround. Note that the brightness and lightness matching criteria in this study produced equivalent results under both of these surround conditions. The study of Kozaki (
1963) also showed that the inducing surround exerts an effect on the brightness of target (test) patches that are increments. Equal reflectance test patches decreased in brightness/lightness with increasing inducing surround reflectance. Diamond (
1953), in agreement with Economou et al. (
2007), reports little effect. However, it is possible that a small effect could easily have been missed in the study of Diamond (
1953) since the inducing and target (test) patches were adjacent squares, a stimulus configuration that produces much weaker induction than when the inducing field completely surrounds the target (test) patch (Heinemann,
1972). In addition, two older demonstrations (Cornsweet,
1970, p. 279; Shapley,
1986) as well as two recent studies specifically designed to test the hypothesis that surround luminance has no differential effect on incremental target patch brightness/lightness (Bressan & Actis-Grosso,
2001; Rudd & Zemach,
2005) clearly show an effect of background luminance on the brightness of test patch increments and contradict the results of Economou et al. (
2007). Bressan and Actis-Grosso (
2001) demonstrated that while a differential simultaneous lightness contrast effect is observed for incremental target patches, and thus does not support the predictions of the anchoring model (Gilchrist,
2006; Gilchrist et al.,
1999), the strength of the effect depends critically on both the surround and target patch luminances. For example, they found that the inducing effect of surround luminance, i.e., the magnitude of perceptual darkening of the target patch as a function of increasing surround luminance, increased with target patch luminance, but that the effect was not significant until target patch luminance exceeded 29.75 cd/m
2. Bressan and Actis-Grosso (
2001) ascribed what they thought were failures of previous studies or conditions (Arend & Spehar,
1993b; Gilchrist,
1988; Heinemann,
1955) to demonstrate a differential lightness contrast effect for incremental target patches on variable surrounds, to surround and/or target patch luminances that were not optimal for producing the effect. According to this explanation, the target patches used in the study of Economou et al. (
2007) should have been of sufficient luminance (34.26 cd/m
2) to elicit only a small effect. Interestingly, however, Rudd and Zemach (
2005) used very low luminance targets (tests) and surrounds (e.g., the incremental test patches never exceeded 3.16 cd/m
2) but found nonetheless that luminance matches to incremental target (test) patches were influenced by the luminance of their surrounds and, like Bressan and Actis-Grosso (
2001), concluded that their results contradicted predictions of the anchoring model (Gilchrist et al.,
1999). Rudd and Zemach (
2005) discussed the possibility that one reason their results differed from previous studies was the limited number of matching steps available with the 16-step Munsell matching scales used in several of the previous studies (Agostini & Bruno,
1996; Gilchrist,
1988; Jacobsen & Gilchrist,
1988). The coarseness of the matching scales could easily mask the differences observed in studies employing finer scale luminance matching (Arend & Spehar,
1993b; Bressan & Actis-Grosso,
2001; Heinemann,
1955; Rudd & Zemach,
2005). This explanation for the failure to detect an effect of background luminance on the brightness/lightness of incremental target (test) patches could also apply to the study of Economou et al. (
2007). The controversy associated with this topic made it of interest to reexamine staircase simultaneous brightness/lightness contrast stimuli for both target patch increments and decrements and to compare these data with the predictions of the ODOG (Blakeslee & McCourt,
1999,
2001,
2004) and anchoring models (Gilchrist,
2006; Gilchrist et al.,
1999).