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Rainer Mausfeld; Modes of appearance revisited: the non-unitary of colour codes. Journal of Vision 2004;4(11):28. doi: 10.1167/4.11.28.
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The concept of ‘modes of appearances’ has an odd status in colour science. As a purely descriptive concept, which has emerged from attempts to classify well-established phenomenological observations of different ‘types’ of colour appearance, it is itself in need of an explanation in terms of some abstract principles of the internal coding of colour. Still, colour science has, by and large, downplayed the theoretical importance of corresponding observations by considering them as extraneous to colour proper and ascribing them to the effects of ‘viewing conditions’ or ‘context’: Different ‘modes of appearance’ are thus not regarded as different types of colours but simply as modifications of the same colour — namely the colour directly tied to the receptor excitations elicited by the local incoming light stimulus (as produced by the ‘aperture mode’) and transformed and modified in subsequent stages of processing. Such an approach rests on the assumption that ‘colour’ constitutes a homogeneous and unitary domain with respect to the ‘data format’ or set of representational primitives in which ‘colour’ figures, and that, furthermore, issues of processing can be investigated independently of the structure of representational primitives. However, this assumption, apart from being ill-motivated from a functionalist point of view, conflicts with well-established core observations: These range from ‘modes of appearances’, and phenomena, where two different colour appearances can be simultaneously present at the same ‘location’ as distinctive aspects of the percept (such that changes in one of these aspects cannot be compensated by changes with respect to the other), problems encountered with asymmetric colour matches, to appearances of ‘material colours’ (which colour science has notorious difficulty to deal with in a theoretically satisfactory way). In contrast to this assumption, various lines of converging experimental evidence suggest that the internal processing of colour is based on (at least) two different types of data structures or representational primitives, which give rise to two proprietary types of colour codes, pertaining coarsely to the ‘colour of an object’ and the ‘colour of the ambient illumination’, respectively. Accordingly, the different ‘modes of appearance’ mirror internal colour processes of an essentially different nature (including mechanisms for dealing with vagueness, ambiguity, and continuous transitions in relevant input characteristics), and, in line with various types of observations and experimental findings, indicate that ‘colour’ exhibits different coding properties with respect to different types of representational primitives. In particular, experimental evidence suggests that the ‘colour’ parameters of the representational primitives involved are, in characteristic ways, intrinsically interwoven with other parameters of these primitives, such as ‘texture’, ‘depth’, ‘motion’ etc. Because of this, it is highly unlikely that an assignment of values to the respective ‘colour’ parameters can be made on the basis of relations on or transformations of retinal colour codes alone (as computational schemes solely based on colour codes presume). After a brief discussion of the above-mentioned issues, I will report experimental results on the segregation of the retinal colour code into a dual colour code and on colour-related input properties (e.g. scene statistics) that modulate such a segregation.
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