Hostname: page-component-7c8c6479df-nwzlb Total loading time: 0 Render date: 2024-03-28T11:01:55.138Z Has data issue: false hasContentIssue false

Do opponent process theories help physicalism about color?

Published online by Cambridge University Press:  01 December 2003

Justin Broackes*
Affiliation:
Department of Philosophy, Brown University, Providence, RI02912

Abstract:

Byrne & Hilbert (B&H) give some excellent replies to the objections to realism about color. However, the particular form of realism they propose, based on opponent processing, prompts several challenges. Why characterize a color by its tendency to produce an intermediate brain signal, rather than in terms of the final effect – either a perception or a neural substrate for it? At the level of the retina, and even of the cortex, there are processes that partly parallel the structure of color experience; but the correspondence is not exact. Must we assume that there is any place in the brain where an exact structural correspondence is found? At the level of psychophysical functioning, there is indeed opponency; but it is not clear that this gives us the kind of type-reduction that B&H want.

Type
Continuing Commentary
Copyright
Copyright © Cambridge University Press 2004

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Notes

Commentary on Alex Byrne & David R. Hilbert (2003). Color realism and color science. BBS 26(1):3–21.

1. One could raise further questions about the psychophysical opponent theory. It is all too easy to suppose that it provides ready measures, for example, for the degree of reddishness or greenishness. But is the amount of red light needed to cancel the greenness of a stimulus really an accurate measure of its degree of greenness? There may also be a disparity between the results of cancellation and direct matching methods (see, e.g., Ingling et al. 1978; Wyszecki & Styles 1982, pp. 652–54). Further, a quick look at the Hurvich and Jameson color response functions tells us that the non-unique spectral stimuli often have higher values on those functions than the unique stimuli do. A yellowish green of 525 nm would count as “greener” than a unique green of 498 nm – because, indeed, it needs more red to desaturate it and cancel any apparent greenness. We might well decide to adopt amount of red for cancellation as our criterion in the future for degree of greenness; but then it would be unclear that we were talking of the same old property as when we judged degree of greenness by our ordinary standards. Of course, there is no requirement for opponent process theorists to identify degree of redness, and so on, with values of these particular functions. But B&H are indeed attracted by a fairly direct identification, linking R (for reddishness) with the value of the (LM) function, for example (sect. 3.2.3).

2. Hurvich and Jameson define chromatic response functions for the CIE 1931 standard observer as 1.0x(λ)-1.0y(l) and 0.4y(l)-0.4z(l). Re-expressing these functions in terms of the König cone response fundamentals (here called L, M, and S), we get the functions I specify here. (These are my own calculations from the standard definitions of the König fundamentals in Wyszecki & Styles 1982, pp. 604–608; see also pp. 457–58, 643–44.) Of course, the CIE data have their own problems, and the König fundamentals inherit them; using newer and better cone fundamentals, we could calculate corresponding hue cancellation functions; they would be equally unlikely to give the output of particular brain processes.

3. As evidence of B&H's drive to find a parallelism, one might cite their rejection of the CIE system, because CIE coordinates “do not capture perceived similarity relations” (target article, sect. 3.1.1). I would submit, however, that to suppose we will find a couple of parameters of brain representations in, say, V4, that capture perceived similarity relations better than the CIE coordinates do, is quite unnecessary. There are indeed divergences between the CIE spaces and perceptual color space; but we should not expect a simple relation between brain representation and perceptual color space either.

PDF 142.5 KB