S. Nishida and M. Shinya (1998) found that observers have only a limited ability to recover surface-reflectance properties under changes in surface shape. Our aim in the present study was to investigate how the degree of surface-reflectance constancy depends on the availability of information that may help to infer the reflectance and shape properties of surfaces. To this end, we manipulated the availability of (i) motion-induced information (static vs. dynamic presentation), (ii) disparity information (with the levels "monocular," "surface disparity," and "surface + highlight disparity"), and (iii) color information (grayscale stimuli vs. hue differences between diffuse and specular reflections). The task of the subjects was to match the perceived lightness and glossiness between two surfaces with different spatial frequency and amplitude by manipulating the diffuse component and the exponent of the Phong lighting model in one of the surfaces. Our results indicate that all three types of information improve the constancy of glossiness matches--both in isolation and in combination. The lightness matching data only revealed an influence of motion and color information. Our results indicate, somewhat counterintuitively, that motion information has a detrimental effect on lightness constancy.

The disparity of highlights on specular reflecting surfaces usually differs from the disparity of the surface points. A. Kirschmann (1895) proposed that this fact may be used as a binocular cue for gloss perception. This was confirmed by A. Blake and H. Bülthoff (1990) who found that subjects judged the glossiness of convex ellipsoidal surfaces as most realistic if the disparity of the highlights was close to the physical correct one. Extending on this finding, we investigate more closely whether the effect of highlight disparity depends on the sharpness of the highlight and the relative amount of diffuse and specular reflection. We measured the effect of highlight disparity on both perceived strength and perceived authenticity of gloss. We used complex, three-dimensional curved surfaces that were stereoscopically presented on a CRT. The reflection characteristics were varied using the Phong lighting model. Highlights were presented either with or without highlight disparity. In a rating experiment, subjects were asked to judge the strength and the authenticity of the perceived surface glossiness. The presence of highlight disparity lead to an enhancement of both the authenticity and the strength of perceived glossiness. The latter finding was confirmed in an additional matching experiment.

Centre-surround stimuli evoke colour appearances (resembling surface colours) which cannot be produced by a single homogeneous spot of light alone (eg brown or grey). Although this seems of great impact to a general theory of colour (including 'colour constancy'), the psychophysics of these 'minimal relational stimuli' is still less well understood than often assumed. On the basis of empirical as well as theoretical observations concerning centre-surround-type stimuli we introduce a relational model of colour coding. At the core of this model is the concept of a three-dimensional linear incremental colour code which behaves differently for increments and decrements. This model takes into account results on 'discounting the background' mechanisms and it is closely related to ratio-based relational concepts and to certain opponent-colour theories. In addition, it provides an analogue to the classical distinction between light and object colours, and covers colour appearances related to object colours as well. Within the conceptual framework offered, problems of complex colour perception (eg 'colour constancy') and judgmental modes are discussed. Conclusions regarding general limitations of three-dimensional modelling in colour perception are derived and corresponding refinements of the relational perspective are briefly outlined.

The field of colour perception has often been praised in recent years as a paradigm of cognitive science. While this certainly has some validity, it contrasts with the fact that the field makes very little contact with the sort of inquiries into mental representations to be found elsewhere in cognitive science (understood as naturalistic inquiries of the mind/brain). I find this quite puzzling, because in the earlier literature of the field it was clearly recognised-for instance by Bühler, Gelb, Kardos, Koffka-that ʹcolourʹ could be understood only as part of the general problem of perceptual representations. Their insights could not, of course, take advantage of the theoretical language provided by what has been called the cognitive revolution. For that reason, and also because they were overshadowed by the success of more technical fields, they fell almost entirely into oblivion. The technical fields, successful with respect to their own specific goals, were colorimetry, neurophysiological investigations into peripheral colour coding, and more recently, functionalist-computational approaches that emphasise certain pre-given performance criteria.. The success of these fields has not been hampered by the fact that they share certain common-sense conceptions of colour, particularly the idea that colour is an autonomous attribute that can be studied almost in isolation from other perceptual attributes. Because such common-sense conceptions of colour appear to be, by and large, innocuous to advances in these fields, no need has arisen so far to relinquish them. However, precisely because of the successes of these fields inquiries into colour perception, understood as the endeavour to develop explanatory frameworks for the role of ʹcolourʹ within our perceptual and cognitive architecture, have suffered a less fortunate fate. The conceptual vocabulary which inquiries into colour perception 1 borrowed from fields, such as neurophysiology, that pursue different explanatory purposes has remained alien to its intrinsic structure and has veiled its core problems. My interest in colour perception (which, a long time ago, was incited by Russellʹs Problems of Philosophy) has been motivated by the question of how we can, within naturalistic inquiry, describe the conceptual structure with which our perceptual system is biologically endowed. Such questions have long been pursued in ethology and have yielded intriguing results. The theoretical picture that is emerging has gained further support from other fields of inquiry, ranging from phenomenological observations to studies with newborns. Though our understanding of the principles of perception is still quite thin, it is, I believe, to a large extent the result of ethological inquiries that unifying principles seem to appear at the horizon. In the chapter I tentatively explore a line of thinking, inspired by ethology, that tries to break away from common-sense conceptions of colour that in the context of scientific inquiry appear unmotivated. I argue that ʹcolourʹ is not a hom...

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