The inverted spectrum thought experiment posits that you (the subject) wake up one morning to find that your colour spectrum (or some part of it anyway) has inverted. This experiment has important implications for the idea of "qualia". While we may not have a way to manipulate qualia directly, this experiment still seems like it would be valuable to conduct. In Daniel Dennett's version of the experiment - "alternative neurosurgery" - he points out that you wouldn't know if your optic nerve was messed with, or your memories, and I would extend this to any apparatus that inverts spectrum at any point along the sensory pathway.

I imagine that the technology to develop goggles (similar to the prism glasses, colour filters, distortion lenses, etc, used in perceptual adaptation experiments) that invert colour is available. However, I have not seen any reference to such an experiment being conducted. Has it? And if not, why not? Are there practical limitations?

It seems to me that the construct of qualia hinges on there being some property of experience that is independent of behaviour/function/physical state, and the subjective experience of colour is often touted as a perfect example of this, via the inverted spectrum experiment. So then the practicality of this experiment - whether or not an inversion of some kind is possible without a functional impact - is crucial. If the experiment cannot be conducted because no inversion exists that can be done without functional impact, then it would constitute a severe blow to qualia as independent of function, and conversely, if it can be done, and the effect shown to be independent of behaviour, then it would surely be a problem for functionalism... So why not try it?


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I don't think inverted prism goggles would be a satisfactory way to empirically test the thought experiment. A key axiom of the argument is that there are no physical changes to our brains or bodies; only the qualia have changed. In a goggles design, there would be a clear physical locus of the change (and we might reasonably call this part of your body for the duration of the experiment), so the shift in qualia would have a clear physical basis.

  • $\begingroup$ Can this be changed to a comment instead of an answer? The question is more about the practicality of conducting the experiment than about its philosophical value. There is already a ton of literature arguing about the value of the experiment, its implications, and which elements of it are important vs which ones aren't. For example, Daniel Dennett's modified version clearly permits physical changes. $\endgroup$
    – Arnon Weinberg
    Jun 25, 2015 at 18:52
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    $\begingroup$ I can delete it, or perhaps revise it, but I think that the broader point is still valid: the practicality of doing the experiment is tied up in whether or not the experiment has philosophical value. Are there philosophers who would accept the evidence that this experiment could produce as being useful? $\endgroup$
    – Josh
    Jun 25, 2015 at 19:24
  • $\begingroup$ Yes, for sure, apart from Daniel Dennett, there is Ned Block who actually uses inverted spectrum lenses in his Inverted Earth variation. I agree that the practicality of the experiment is restricted by its philosophical value - that is the point of the question: if there really is no way to conduct the experiment, then it poses a severe challenge to qualia. But that's different from saying that it is practical to do but there is no point in doing it because it doesn't meet the criteria of some variations of the experiment. $\endgroup$
    – Arnon Weinberg
    Jun 25, 2015 at 19:39
  • $\begingroup$ "A key axiom of the argument is that there are no physical changes" And here is the problem. We don't know if perception can become different without physical changes. Not for a physicalist for sure. $\endgroup$
    – rus9384
    Sep 23, 2018 at 1:26

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