The natural center of chromaticity space is not always achromatic: A new look at color induction

Abstract

Although current theories of color vision differ in many respects, they all assume the existence of a uniquely defined neutral point in chromaticity space. It generally is assumed that this point satisfies several criteria simultaneously. One of these criteria is that it is perceived as achromatic. A further criterion shared by most theories is the structural assumption that lines in chromaticity space of constant hue converge on the neutral point. The basic assumption that these two criteria coincide is clearly true for isolated spots of light presented in darkness, and it usually is taken for granted that this coincidence generalizes to more complex visual stimuli. Here, we show that this is not the case. Our experiments with infields in chromatic surrounds revealed that the point in chromaticity space that appears gray is clearly different from the point on which lines of constant hue converge. A plausible interpretation of this apparently paradoxical finding in terms of color scission is proposed.

New Laws of Simultaneous Contrast?

“…The first one is necessary because targets embedded in uniform surrounds have been noted to assume a dual colour impression reminiscent of perceptual transparency (Metelli, 1970), particularly when the contrast between target and surround is low Masin & Idone, 1981;Brown & MacLeod, 1997;Mausfeld, 1998;Ekroll et al, 2002Ekroll et al, , 2004. According to our experience, the target is then perceived as consisting of two layers, whereby one layer is perceived as coextensive with the target region and the other as extending across both the target and the surround.…”

“…As can be seen, the loci of constant hue converge on the chromaticity of the surround. Thus, the direction hypothesis and the size hypothesis can account for the 'convergence paradox' observed by Ekroll et al (2002). The loci of constant hue are slightly curved, but if they are approximated by straight lines (dashed lines in the middle panels) the rotations of hue angles observed by Hansen et al (2007) are evident.…”

“…The direction hypothesis and the constant size hypothesis (or the inverse size hypothesis) can also account for some further challenging and ill-understood findings, namely the 'convergence paradox' reported in Ekroll et al (2002) and the rotation of constant hue lines observed by Hansen et al (2007). Simultaneous contrast is often measured using achromatic settings (Helson & Michels, 1948;Werner & Walraven, 1982).…”

“…Simultaneous contrast is often measured using achromatic settings (Helson & Michels, 1948;Werner & Walraven, 1982). In Ekroll et al (2002), though, we used alternative, indirect methods which -resting on standard assumptions about the topology of the space of perceived colour -should also be suitable for determining the location of the achromatic point. One of these methods was to determine the point at which lines of constant hues converge, which should be the achromatic point.…”

“…Our arguments in favour of these claims are based on many seemingly disparate and unrelated lines of evidence and recent developments in our understanding of simultaneous colour contrast (Brown & MacLeod, 1997;Gordon & Shapley, 2006;Hansen, Walter, & Gegenfurtner, 2007;Ekroll, Faul, Niederée, & Richter, 2002;Ekroll, Faul, & Niederée, 2004;Ekroll & Faul, 2009;Ekroll, Faul, & Wendt, 2011;Faul, Ekroll, & Wendt, 2008). The main point we wish to make is that many different and seemingly unrelated empirical findings which have accumulated over the years and all appear surprising and challenging from the the traditional point of view can be reinterpreted as converging evidence for the simple principles laid out in the above hypotheses.…”