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Qualia are phenomenological (the subjective experience of the physical activity of the brain). But how does phenomenology feed back into the activity of the brain? That is, how can the physical brain detect that qualia are occurring inside of it and be able to report on it?

To clear up confusion:

  1. Suppose that all things are physical and all behaviors can be explained physically through neurons.

  2. Suppose that qualia exist and are phenomenological.

The question is, how do physical neurons "know" about qualia. This is similar to a mind-affecting-brain question, but subtly different:

  1. There is no assumption about a "mind" existing

  2. The causal relationship between qualia and physical brain is restricted to the physical brain's detection of qualia.

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    $\begingroup$ This question also builds in the assumption that qualia are non-physical. Most cognitive scientists think that qualia are physical phenomena, just ones that we don't understand the mechanistic basis of yet. $\endgroup$ – Josh de Leeuw Jun 7 '15 at 18:10
  • $\begingroup$ I agree that everything can be explained physically, and that the generation of qualia, as far as we know, has a physical basis. The question is very restricted to the detection of qualitative experience by the physical brain. $\endgroup$ – deleteme Jun 7 '15 at 18:43
  • $\begingroup$ For example, what would physically be happening (with neurons in a brain) to cause the following behavior: A person says "I experience qualia, and it is non-physical." Unless the person were lying about the existence of such a thing (qualia), this behavior makes no sense, and has no origin. $\endgroup$ – deleteme Jun 7 '15 at 18:54
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    $\begingroup$ There is still an assumption here that qualia are non-physical. Points 1 & 2 contradict each other (all things can't be physical while qualia are non-physical). I think this assumption is important because all of the difficulty in answering this question goes away if qualia are accepted as a physical thing. It won't explain what qualia are, but it removes the problem of explaining how the physical brain could interact with qualia. $\endgroup$ – Josh de Leeuw Jun 7 '15 at 19:25
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    $\begingroup$ @ArnonWeinberg this question is perfectly fine here. Philosophy of mind is a part of the cognitive sciences and we are not restricted to empirical questions. In fact, drawing a clear line separating 'science' from 'philosophy' is often a fool's errand. $\endgroup$ – Artem Kaznatcheev Jun 7 '15 at 23:12
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Keep in mind that "qualia" is a philosophical construct whose purpose is largely to stimulate thought and discussion about subjective experience, definitions, and potential empirical implications. The construct may well turn out to be untenable, but either way, it ought to be useful for elucidating issues relating to "the hard problem".

Your question is a very good one, and has spurred much debate over the nature and meaning of qualia. Qualia are often regarded as somehow independent of physical properties, but yet as you point out, they clearly affect behaviour somehow. Here are some points to consider:

  • One way out of the conundrum is to deny qualia as a useful construct. Critics of qualia address the issue of subjective experience without qualia in a variety of atlernative ways.
  • Duality is another approach to qualia, but is not a commonly held view in science. A more subtle approach is epiphenomenalism, which is a type of dualism that denies qualia any causal role. However, as you've rightly pointed out, the mere fact that we are discussing qualia suggests that it does have a causal role.
  • It has been suggested that qualia actually have 2 distinct aspects: An experience that is "ineffable" - cannot be described and does not have a causal role - and a knowledge of the experience that does have a causal role. While this approach minimizes (or at least constrains) the causal role of qualia, it does not entirely deny it.
  • Functionalism is a common alternative to dualism that comes in many varieties, and several related approaches with similar postulates (eg, behaviorism, physicalism, and computationalism), suggest that qualia (if they are meaningful at all) supervene on physical systems - that is, they are a natural and direct property of them. In some interpretations, this makes qualia "independent" of phsyical systems only in the sense that they describe different properties than the cause and effect that we normally focus on, but not in the sense that they can possibly be separated from them as some other interpretations of qualia suggest. However, many thought experiments about qualia suggest a stronger independence, so therefore, not all varieties of functionalism are compatible with all interpretations of qualia.
  • Another approach worth mentioning is representationalism, a view that sort of side-steps the cause-and-effect issue by defining qualia as indirect internal representations of external stimulus (objects). As there are so many varieties of representationalism, it is difficult to pin down what exactly this means for qualia's effect on the brain, but the general gist of it is that qualia are viewed as constructs of the mind that are representational (meaningful) rather than real (causal).
  • Of course, another common response is that we just don't know, and may never know, as we simply don't have the intellectual capacity to understand - formally, cognitive closure.

There are lots of other approaches that attempt to address the question in yet other ways, but hopefully that's a good summary of the major categories anyway.

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