Colour, psychophysics, and the scientific vs. manifest image of reality

Recently on TheEGG, I’ve been writing a lot about the differences between effective (or phenomenological) and reductive theories. Usually, I’ve confined this writing to evolutionary biology; especially the tension between effective and reductive theories in the biology of microscopic systems. For why this matters to evolutionary game theory, see Kaznatcheev (2017, 2018).

But I don’t think that microscopic systems are the funnest place to see this interplay. The funnest place to see this is in psychology.

In the context of psychology, you can add an extra philosophical twist. Instead of differentiating between reductive and effective theories; a more drastic difference can be drawn between the scientific and manifest image of reality.

In this post, I want to briefly talk about how our modern theories of colour vision developed. This is a nice example of good effective theory leading before any reductive basis. And with that background in mind, I want to ask the question: are colours real? Maybe this will let me connect to some of my old work on interface theories of perception (see Kaznatcheev, Montrey, and Shultz, 2014).

From psychophysics to the cellular basis of colour vision

As somebody with some physics background, when I think of the founding of modern psychology, I usually don’t think of Sigmund Freud, but Hermann von Helmholtz instead. To a modern reader, physics, physiology, and psychology might seem like distant fields, but in Helmholtz time these fields were just starting to disassociate themselves and many critical questions of natural philosophy lay at their intersection.

Toward the end of the 1800s, the development and refined understanding of Maxwell’s electromagnetism was taking the scientific image of light and vision further and further from the common sense manifest image of colour and perception. The natural philosophers of the day (the more accurate epithet, given that the title of ‘scientist’ was still struggling for acceptance at the time) could calculate more and more exciting physical properties of light, but could say very little about our subjective experience of light. Helmholtz wanted to reconcile these views by focusing on the physiology and psychology of vision.

In 1850, building on the ideas of Thomas Young, Helmholtz developed the phenomonological trichromatic theory of colour perception. We still use this theory today, although — after Svaetichin’s (1956) work with fish and Dartnall et al.’s (1983) work with humans — we can now rely not just on self-reported perceptions but also know the cellular basis for the photosensitivity: our rods and cones. It is our three types of cones that are responsible for implementing the three dimensions of our colour vision that Helmoltz identified. So, in some sense, Svaetichin (1956) and Dartall et al. (1983) provide the details of the transformation that maps the reductive world of wavelengths to the effective world of colour.

The knowledge of rods and the three types of cone cells is definitely important, but in many ways this physical basis is less important than the psychophysical tradition that Helmholtz (along with Weber, Fechner, and others) established. They build an objective science on the foundation of subjective experience, and they were able to predict the basic structure of the relevant physical basis, without having the ability to study it explicitly. In the context of biology, this is kind of how Schrodinger described many of the properties that DNA would need to have, over a decade before the structure of DNA was uncovered.

It is also important to realize that our increases in understanding of the biological basis of basic processes does not reduce the need for phenomenological approaches that take self reporting as serious evidence. It just moves the approach to more interesting questions, where knowing the basic building blocks is not enough given our lack of knowledge about structure and information processing. My favourite example of this is the interaction of language and colour perception.

Colors and the tension between the scientific and manifest image

So given that we’ve found the transformation that maps our effective theory (psychophysics) onto our reductive theory (physics) does that mean that we can confidently and affirmatively answer the question: Are colours real? Or Nemu Rozario’s more precise statement on the CogSci StackExchange: is there any experiment which can tell us the color we see is the only and real color which is reflected by the object?

The below considerations are based on my old 2013 answer to the question: are colours real?

Usually, for something to be ‘real’, we want it in some reasonable manner to be objective or (because that is extremely vague) at least very consistent across subjective observers. Unfortunately, colour does not satisfy this.

Let’s go through the levels of description:

  1. Physical basis. Physics does not have colour, it just has a continuous spectrum of wavelengths. Even when you look at the sensitivity of the 3 types of cones in the retina it is not discrete, but continuous. The categories of colours (i.e. “that’s red”, “that’s blue”) are produced by perception and these discrete-ish categories form the basis of colour qualia. Scientists can study these categories by asking participants if various stimuli feel like the same colour. The qualia of colour are not the same kind of thing as wavelengths of light. Instead, our colour qualia are an interface through which we interact with the physical world (Hoffman, 1998; 2009).
  2. Biological variation. As I mentioned above, most people have 3 types of cones, and a typical colour-matching experiment in the style of Helmholtz need 3 dials to tune a colour to be indistinguishable (by them) from one they see presented to them. However, there are colourblind individuals where 1 (or more) of the cone types are not expressed; such individuals only need two knobs to match a presented colour, and thus they will identify certain colours as the same though most people would experience them as different colours. Finally, there is the rare condition of tetrochromacy (much more common among women than men) where an individual has 4 different types of cone cells. For most of these individuals, this does not result in being able to reliably distinguish colours that trichromats perceive as the same, and they are called non-functional tetrochromats. However, there have been reported cases of functional tetrochromats; such individuals are able to reliably distinguish colours that would be identical to trichromats.
  3. Cross-cultural variation. Regier & Kay (2009; see also references within) discuss how these arbitrary boundaries between colours are language-dependent. Thus, the nuances of colour do not meet the psychological definition of a human universal even within people with the same biology. This is especially interesting to me, if we want to potentially use colour perception as an example of a social interface (Kaznatcheev, Montrey & Shultz, 2014).
  4. Intra-personal variation. The buck doesn’t stop there. Gilbert et al. (2006) showed that the language dependence is supported in the right visual field (across from the ‘language center’ of the brain) but not the left. In other words, when I present colours in one part of your visual field, you experience them one way, and when I present them to the other, you then experience them in a fundamentally different way. This isn’t an artifact of some physical property of your eyes, but of how your brain perceives colours (i.e. feedback from higher-order parts of the brain).

All of these considerations can be especially useful when thinking about the classic inverted-spectrum problem. It is most popularly stated as: What if someone perceives a color as ‘red’ when it is actually ‘green’?

So what does this mean for the reality of colour? On the one hand, we can clearly say that colours aren’t real. But on the other hand, this feels clearly absurd. Like we missed the point of the question. This is the tension between the scientific and manifest image of reality. In the scientific image of reality, colours are not real. In the manifest image, they are. And contrary to their names, we see from Helmholtz that we can do science at either level.

But the mapping between these images in extremely complicated and variable. A grander version of the complicated mappings between the reductive and effective theories that I usually study.


Dartnall, H. J. A., Bowmaker, J. K., & Mollon, J. D. (1983). Human visual pigments: microspectrophotometric results from the eyes of seven persons. Proceedings of the Royal Society B, 220(1218): 115-130.

Gilbert, A. L., Regier, T., Kay, P., & Ivry, R. B. (2006). Whorf hypothesis is supported in the right visual field but not the left. Proceedings of the National Academy of Sciences of the United States of America, 103:(2), 489–494.

Hoffman, D.D. (1998). Visual intelligence: How we create what we see. W.W. Norton, New York.

Hoffman, D.D. (2009). The interface theory of perception. In: Dickinson, S., Tarr, M., Leonardis, A., & Schiele, B. (Eds.), Object categorization: Computer and human vision perspectives. Cambridge University Press, Cambridge.

Kaznatcheev, A. (2017). Two conceptions of evolutionary games: reductive vs effective. bioRxiv: 231993.

Kaznatcheev, A. (2018). Effective games and the confusion over spatial structure. Proceedings of the National Academy of Sciences: 115(8): E1709.

Kaznatcheev, A., Montrey, M., & Shultz, T.R. (2014). Evolving useful delusions: Subjectively rational selfishness leads to objectively irrational cooperation. Proceedings of the 36th Annual Conference of the Cognitive Science Society. arXiv: 1405.0041v1.

Regier, T., & Kay, P. (2009). Language, thought, and color: Whorf was half right. Trends in Cognitive Sciences, 13L(10), 439–446.

Svaetichin, G. (1956). Spectral response curves from single cones, Actaphysiol. Scand. 39, Suppl. 134, 17-46.

About Artem Kaznatcheev
From the Department of Computer Science at Oxford University and Department of Translational Hematology & Oncology Research at Cleveland Clinic, I marvel at the world through algorithmic lenses. My mind is drawn to evolutionary dynamics, theoretical computer science, mathematical oncology, computational learning theory, and philosophy of science. Previously I was at the Department of Integrated Mathematical Oncology at Moffitt Cancer Center, and the School of Computer Science and Department of Psychology at McGill University. In a past life, I worried about quantum queries at the Institute for Quantum Computing and Department of Combinatorics & Optimization at University of Waterloo and as a visitor to the Centre for Quantum Technologies at National University of Singapore. Meander with me on Google+ and Twitter.

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