Abstract
Synaesthetes persistently perceive certain stimuli as systematically accompanied by illusory colours, even though they know those colours to be illusory. This appears to contrast with cases where a subject’s colour vision adapts to systematic distortions caused by wearing coloured goggles. Given that each case involves longstanding systematic distortion of colour perception that the subjects recognize as such, how can a theory of colour perception explain the fact that perceptual adaptation occurs in one case but not the other? I argue that these cases and the relationship between them can be made sense of in light of an existing view of colour perception. Understanding colours as ways in which objects and surfaces modify light, perceived through grasping patterns and variations in colour appearances, provides a framework from which the cases and their apparent disanalogy can be predicted and explained. This theory’s ability to accommodate these cases constitutes further empirical evidence in its favour.
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Notes
Part of my aim in this paper is to argue for a particular way of understanding synaesthetic colour experience in general. Given this variety in forms of such experience, one might wonder whether a general account is possible. However, as we will see, I attempt to account for synaesthetic experience in terms of general considerations concerning the relationship between apparent and objective properties in colour perception. This account could, as far as I can see, be applied equally to any of the forms of synaesthetic experience listed above. For simplicity’s sake, however, my examples shall concern synaesthetic experiences roughly as of colours overlaid upon graphemes. ‘Roughly’ since, as as I will argue, the way synaesthetic colours figure in experience prevents them from having objective spatial purport. This eventual consequence of my account might be used to explain how and why some synaesthetes experience their photisms as non-localised. Thanks to an anonymous referee for prompting clarification here.
Synaesthetes also exhibit priming and interference effects on perceptual tasks that support the hypothesis that they genuinely experience the illusory colours. There is also evidence that synaesthetic colours can contribute to pop-out effects that aid visual search. See Edquist et al. (2006) for a useful review.
Bompas and O’Regan (2006) note that there has been some difficulty in replicating Kohler’s results. However, the main study they cite in support of this claim (McCollough 1965—the other study cited is an unpublished Master’s thesis) confirms that the colour sensations caused by distorting goggles subjectively fade away over time, questioning only Kohler’s claim that new dependencies of colour perception on eye-movement occur as after-effects of adaptation. Bompas and O’Regan (ibid.) succeeded in inducing such dependencies via a short period of conditioning without goggles. The fact that the distortions caused by the goggles adapt away over time is the most important aspect of Kohler’s results for the case I make in this paper, and seems well established. In what follows I’ll be taking the results that Kohler reports at face value.
It’s not quite right to label the colour appearances that characterise each case ‘illusory’. Subjects wearing Kohler’s goggles really are looking through tinted lenses, and seeing the world in just the way they should in light of this fact. A consequence of the position for which I’ll argue in this paper (particularly in Sect. 3) is that synaesthetic sensations are not strictly ‘illusory’ in that they are not experiences that purport to be of how things are actually coloured, and so don’t make a claim about colour properties that can be assessed as true or false. Both sorts of appearances are, however, ‘illusory’ in being unreliable guides to the way external things are really coloured. With these caveats in mind, I’ll continue to describe the relevant colour appearances as illusory in what follows.
One disanalogy between the two cases is that the causes of perceptual distortion are constantly present for the wearer of the goggles, but only present in certain contexts for the synaesthete. It might be thought that such a difference in reliable presence of perceptual distortion and its causes can explain the fact that adaptation occurs in the former case but not the latter. However, as we shall see in Sect. 4, there are nuances in Kohler’s data on perceptual adaptation which this hypothesis can’t account for. Thanks to Conor McHugh for prompting clarification on this point.
See Churchland (2005) for a fuller account of these colours and how they can be produced, complete with colour plates that let interested readers experience the relevant afterimages for themselves.
For an instance of the first view, see Block (2007). For an instance of the second, see Schellenberg (2008). For what it’s worth, my own sympathies lie with a view according to which apparent and objective properties must be defined interdependently—objective colour properties must be specified in terms of the patterns of appearances which make them up, whilst appearances must be specified in terms of the objective properties which they can help to disclose. See McDowell (2004) for a view with this structure. Noë (2008) is also suggestive of such a view. Unfortunately, spelling out and defending this view is beyond the scope of my task here. As just noted, the account of colour experience developed here is intended as compatible with each of these various possibilities.
Clearly there is much more of interest to be said about the sort of understanding to which I appeal here—in particular about its relation to more advanced, conceptual forms of understanding. However, this brief characterization suffices for our purposes here: making the view under consideration tolerably clear, and setting the stage for the account of synaesthesia and perceptual adaptation which follows.
In the majority of situations—as noted above (n.1) synaesthetic colours can be made to help or hinder certain perception and classification tasks via stroop or priming effects in carefully controlled lab conditions. See Gray (2003) for a description of the Alien Colour Effect, where the colour-naming abilities of coloured-hearing synaesthetes are marginally slowed by incongruity between the colour to be named and the colour of the photism induced by real or imagined perception of the first phoneme in the colour’s name. The presence of these small functional differences between the colour naming and classification behaviours of synaesthetes and non-synaesthetes is compatible with the point I am making here—that synaesthetes perceive objective colour properties sufficiently well that their lack of adaptation only looks puzzling when compared to Kohler’s cases.
Of course, there are important differences between the two sorts of case. For example, as an anonymous referee notes, Kohler’s subjects are in the throes of coping with a new perceptual distortion, whereas adult synaesthetes have a lifetime of experience of their synaesthetic sensations. Perhaps, then, synaesthetic colours are experienced as distortive in infancy, or would be so experienced if suddenly induced in a mature perceiver. The account to be developed below is compatible with these possiblities—it aims to explain how synaesthetic colour appearances figure in the experience of mature perceivers in a way that does not compete with their perception of objective colour. In developing this view, we will achieve a clearer picture of the two cases and their relationship. The juxtaposition of the two cases here serves only to set the stage for an account which adequately explains them both.
Noë (2004, 2008) also uses this example to shed light on the relationship between apparent and objective properties in perception, and the role played for the perceiver by sensorimotor understanding. As noted above, I offer the account of colour experience developed here as an elaboration of his enactive view. Note that the above does not imply that letters or apparent colours cannot be direct objects of experience. If you like, it’s possible (though, I think, surprisingly difficult) to focus only upon the letters on this page, bracketing their significance as constituents of words. But this is certainly not how we usually look at things. Similarly, it’s possible (though difficult) to focus on the ways in which the lit and shaded portions of my wall appear different, bracketing the fact that they are both aspects of the wall’s one true colour. Again, it seems clear that this is not the way apparent colours usually figure in our experience.
Such a perceiver would, of course, be the opposite of a colour-grapheme synaesthete. To my knowledge, no cases of this kind exist.
Little rather than none since, as noted above, synaesthetic colours can cause small impairments in colour naming and categorisation in certain circumstances. Once we see that synaesthetic colour experience can happily coexist with veridical perception of objective colours in the way outlined above there is little temptation to suppose (or so it seems to me) that such small impairments could constitute a sufficient pressure toward adaptation. Non-synaesthetes can be made to exhibit analogous impairments in naming and categorisation as a result of stroop effects (as when identifying the colour of the word ‘green’ typed in red ink), but since semantic and chromatic properties usually coexist happily in perception we need not assume that such cases constitute a pressure toward either semantic or chromatic perception adapting away.
My thanks to an anonymous referee for prompting both these clarifications.
“A blue of one half its initial intensity on the colour wheel was sufficient to compensate for the yellow of the spectacles, and the blue of the spectacles was judged to be completely equal to gray—in other words, the subject no longer perceived it as colour.” (Ibid. p. 114) This fact is also neglected in existing philosophical discussions of Kohler’s results.
Recall the observation from Broackes (1992) about colour-blind perceivers, mentioned in Sect. 2, above. Their colour discrimination is markedly better in free vision than in constrained laboratory settings, suggesting that the impairment in their ability to perceive objective colours is less severe than the impairment in their ability to perceive apparent colours.
Kohler (Ibid., p. 45) explicitly notes the discrepancy between subjects’ reports of adaptation and their abilities in the discrimination task, but offers no explanation of it. A consequence of our view here is that we should expect tests of adaptation to differ in their results according to the extent to which they hold the parameters that fix appearance properties constant, and that the measures suggesting greatest adaptation will be those most closely approximating free vision.
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Acknowledgements
My thanks to Andy Clark, Conor McHugh, Mohan Matthen, Pepa Toribio and an anonymous referee for helpful comments on earlier versions of this paper.
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Ward, D. Why don’t synaesthetic colours adapt away?. Philos Stud 159, 123–138 (2012). https://doi.org/10.1007/s11098-010-9693-y
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DOI: https://doi.org/10.1007/s11098-010-9693-y
Keywords
- Colour perception
- Enactivism
- Perceptual adaptation
- Synaesthesia