As far as I know, the hard problem of consciousness is focused on how the physical and mental states relate. However I haven't been able to find any attempts to answer the question of how identical physical phenomena can create qualia of seemingly fundamentally different qualities. For instance pressure can create the experience of sound, pain, heat, cold, touch and tension depending on which neurons detect it - and once they do, their experiences become incomparable - as if they existed in different dimensions. In other words, you couldn't describe sound to someone deaf from birth using his experience of temperature. At the same time, the distance between these dimensions is probably possible to communicate - for instance the smell dimension is certainly closer to the taste dimension than to the vision dimension.

So are there any theories explaining how neural activity with different functions can generate different sensations?

  • 2
    The electric signals are not the same, they vary in intensity and frequence depending on the neuron and stimulus. Also, the neurons that get activated are not the same, for different stimuli in the same person or for the same stimulus in different person (because each brain grows organically and neurons establish connection during each individual's growth, no two person map the exact same neurons to the same stimulus)
    – armand
    Jan 23 at 13:57
  • @armand Thanks for this clarification. It is why I wrote "in principle" - although your comment made me realize how it's essentially just the hard problem of consciousness - and the question might me better formulated as: How does neural activity with different functions make us feel different? - so I edit it in.
    – Probably
    Jan 23 at 15:23
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    This is one of the 'easy' problems. Philosophically, ie 'in principle', we already understand this. Qualia is about an individual experiencing something in a unique way, a way which cannot be compared because it is from their point of view or subjectivity.
    – CriglCragl
    Jan 23 at 16:33
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    @Conifold Yes, it's part of the hard problem of consciousness. However, what I'm after isn't simply the fact these sensations are different but the fact they seem qualitatively in different dimensions similarly to how the physical and mental world feel like different planes of existence.
    – Probably
    Jan 23 at 22:00
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    Zombies would have the amplification built in physically, but if there is mental causation/parallelism we would expect the effect to be mediated/accompanied mentally. However, I do not see why we should expect differences in phenomenal quality reflect anything metaphysically rather than merely psychologically significant. Information can be coded into strings of letters from the same alphabet, but we have qualitatively different feelings about what is written because of differences in how it concerns us, not because of differences in the physics of reading.
    – Conifold
    Jan 24 at 1:27

Perhaps you will find this answer relevant The Origin of Thought

When we look at the connectomes of simple organisms, we see various 'input channels'. Neurons that specialise in tasks like self-other determination. We can extrapolate that 'primitive' into specialised regions for touch, and proprioception.

When we look at convolutional neural networks, we see how a series of specialised subroutines can operate together: edge detection, 3D shape identification, movement identification etc. Leading to reactions (see the book Thinking Fast And Slow). And building a picture - this relates to the Global Workspace Theory of why we have a mind and unified awareness.

If you look at split-brain patients, where the hemispheres were separated as a medical procedure, it was revealed one hemisphere is focused on integrating information about the self & the body, the other on building a picture of the world. Information from a given channel can contribute to both - eg our sense of balance is primarily visual, secondarily from our ear canal, and also fed information by proprioception - we use these channels in a dynamic way, and we can stimulate better awareness through learning, as people undergoing physiotherapy do (consider how reduction in working memory with ageing makes falls more likely - working memory limits the 'global workspace' size).

The split-brain case illustrates the multi-agent nature of our brains, and how we don't directly experience sensations, but constantly process them and integrate them into a picture that also involves our intentions and purposes - see Donald Hoffman on why we can't rely on evolution to show us reality. Also Anil Seth on why our 'reality' is better described as a useful hallucination.

In your example, we can picture the channels of say heat and pain, as rooted in the role of individual specialised neurons in the early connectome, successively hijacked by additional purposes. Pain is highly subjective, with heat-blistering strongly dependent on attention, and inducible by touch alone under hypnosis. Critical injuries like being shot often don't trigger pain initially, and we consciously trigger the adrenalin to get out of danger - or trigger instinctive responses and go into shock, which may be helpful, or may kill a person. Pain is not best described as a 'sensory primitive', because a lot of processing is done around identifying threats & dangers, with inputs from multiple channels. But there are action-potential thresholds being crossed by specific neurons, which feed into specialised networks linked to particular purposes, and feed into brain regions which abstract useful information into layers of convolutional neural networks, which build a picture, and tag for urgent responses like reflexes, or adrenalin response/fight or flight.


"As far as I know, the hard problem of consciousness is focused on how the physical and mental states relate."

It is necessary to make the distinction between qualia and mental states. A quale is the quality of our subjective experience. Mental states are best understood as the informational content of our mind. Our mental states are in principle open to the empirical investigation typical of the sciences and as long as they keep trying hard, cognitive scientists should be able to improve the science of our mental states, at least up to a point. Qualia seem in principle inaccessible to science. This is somewhat paradoxical since there is nothing we know better than our qualia. I would even say myself that this is the only things we actually know. Everything else can only be believed or disbelieved. However, while seemingly paradoxical, the situation vis à vis qualia can be compared to the fundamental constituants of reality we in principle expect exist. We haven't found these constituants yet, or if we did, we don't know that we did.

But suppose that we did, then how will we explain the nature of these fundamental constituants? The answer is that we will be unable to. You can only explain something in terms of something else: elements in terms of atoms, atoms in terms of elementary particles etc. Once you get to the ultimate ontological furniture of reality, we will have nothing else with which to explain them. We will just have to take them for granted.

Our qualia may be in a similar kind of epistemological trap. We just have to take them for granted.

  • I think everything looks like an epistemological trap for anyone who doesn't dare to go deep enough :) Thanks for the mental states note!
    – Probably
    Jan 26 at 7:07

This blurry picture you have addressed is related to a commonly misunderstood or overlooked concept of emergent phenomena.

It seems to me that neural activities -all those action potentials, local field potentials, neurotransmitter release patterns etc- are simply correlated with qualia and are not the cause of it per se, their orchestrated action is what leads to qualia. Quale is irreducible and emergent, i.e. cannot be solely explained with concepts that form the basis of it. It is much like the concept of life itself. For example, a neuron has as much qualia as a protein by itself has life, I hope that makes the argument clear.

The problem with observing emergent phenomena is that the parts that are composed to form a novel property does not reflect the emergent property per se, that is why you cannot observe how a change in the transfer of information leads to a qualitative change in qualia. This also is the case with life, we cannot just throw in a bunch of biomolecules and expect life to emerge. The idea behind this is that configuration itself is as important as parts themselves.

There also is the possibility that we may lack the science or technology at the moment. If we dissect the compositions of cognition to a certain degree in the future, we may in turn find out a way to rearrange or configure fundamental parts to form qualia. Figuratively, we may even be able to transfer qualia, or make access of it, between each other.

The unique problem of qualia is that we try to liken to with conceptually simpler emergent phenomena, as we naturally attach it a special degree of uncertainty because of the explanatory gap. We have to accept qualia as is, just as we have to accept "life" as is. There also is not a physical description of "life" itself, based on physical laws. The information that exists about "life" is limited to mechanistic explanations.

Consider the following example: A flock of birds might have a quale, but we cannot know, as we cannot have direct access to it just like we don't have access to each other's qualia.

These claims are not my own but are derived from the collection of ideas by Gestalt psychology, holism, complex & dynamic systems theory, AI, cellular automata and more importantly Minsky's Society of Mind thesis.


Note: From the Latin, singular "quale" (kwah-lay), plural "qualia" (kwah-lee-ar)

The brain processes vastly complex information. Yet it operates on a small number of design principles, such as neuronal firing patterns and synapse strengths between neurons. The same basic circuit elements are repeated billions of times but each is connected subtly differently, just like a digital computer. The complexity comes from the configuration of these elements in order to encode information. For example a small slice of the optical processing region looks much like a small slice of the auditory processing region. What distinguishes them is that one is encoding sound information and the other is encoding vision information. Indeed, they are alike enough that a musician's audio region will steal some processing capacity from nearby to enhance their aural acuity.

It is the injection of this information from the processing centres into the conscious region of the brain which invokes the associated qualia. Even here, the same pattern of neuronal firing will, in different places, invoke different qualia. So it is the nature of the information which is what defines the quale it invokes.

This nature is largely pre-programmed or learned by the infant brain. But how and why the brain can tell one kind of information from another remains unknown. We at least know that it maintains a model of the self, so presumably it tracks which information is attached to which part of the model. A very simple parallel might be my computer desk top, which has several windows open; how does it know which app to display in which window? One might suggest that the neural equivalent is as much an unsolved problem of computer science as of neuroscience. This seems to address your main question.

Of course, having been received and identified, how does this conscious information invoke its particular associated quale? This is the "hard problem" which appears intractable to science.


I do not know of such a theory. But I offer some related thoughts that impinge on what it might look like:

Some dedicated meditators claim there is only one qualia. Practitioners of Advaita Vedanta claim all of experience is made of sat-chit-ananda, which is one substance (the triune term is just capturing the one thing to describe it better), which translates to being-awareness-peace, even negative emotions ultimately, even self and consciousness. Consciousness is constructed of it, just like everything else. (Take care with terminology; some call chit “consciousness” and they call what I just called consciousness “awareness”, which to me at least seems obviously backwards). The equating of being and awareness comes from a deep first-person analysis of where the boundary is between a sight and one’s awareness of it to find it isn’t actually there but is constantly superimposed by automatic thinking that was previously unnoticed. Even buddha said dhammas were made of mind (chit) and consciousness was something else. There is only one first person atom, sat-chit-ananda, but in this case it makes thoughts and absolutely everything.

I saw some research that people process different senses in similar ways. One example is that researchers showed someone nonsense letters and played sounds and participants largely agreed on whether the letter fit the sound (a jagged line for a jagged sound etc). And now related findings that different senses are processed using overlapping portions (below the sense cortexes, visual cortex, auditory cortex, etc). I think the distance between senses is less clear than you said because smell is used when eating and part of determining flavor, so that might be why they seem close. I haven’t decided and never thought about that. In Buddhism, sense data when consciously perceived (as opposed to unconsciously used for some functioning like navigating or being unconsciously affected in your analytical comments by someone’s facial features) always has a vedana to it, a feeling tone, which is a visceral “yum” or “yuck”, even if only slight. So while there may or may not truly be different sense qualia, they have common experiential roots.

Some of the above, if rigorously thought-out and further researched could definitely end-up in a theory of how natural phenomena generate different qualia. Could be done from the brain side (and arguably has been begun just based on the discovery of sense cortexes and furthered based on overlapping regions of processing for different sense data) or the subjective side (and arguably has been attempted by some Indian religious figures and meditators from that side ending in one meta-qualia in at least one case (advaita)).


First of all, qualia are inaccessible to science; they are not verifiable by any independent observer. Yet they are the foundational experiences which any scientific observer relies on in order to observe anything. They thus represent one of life's profoundest mysteries.

They appear, subjectively, to accompany certain kinds of information generated by brain activity. Indeed, the way in which their distinctive qualities are experienced is a perfect match to the way in which those pieces of information are distinguished. You ask why this is? There are two aspects to that:

  • If they did not reflect every nuance of the information of which we are conscious, they would be useless. For example I have very poor musical pitch, consequently so many aspects of my musical qualia appear subtly indistinguishable that I had to give up learning the violin. So the property you ask about is simply an imperative.
  • Digging any deeper into a profound mystery requires some other aspect of that mystery to relate to. Suitable aspects appear sadly lacking. The ultimate answer, as to how the trick is pulled, remains a part of that mystery.
  • Thanks. However, I don't think evolution is a useful framework here. We can probably both agree consciousness depends on some information phenomena and therefore is somewhat of a physical law. However, you cannot infer it from physics. Thus, a planet where philosophical zombies would evolve is entirely imaginable just like we don't imagine computers to have consciousness.
    – Probably
    Jan 26 at 7:17
  • Similarly, if there wasn't gravity, we wouldn't evolve - thus, one might argue - the ability to be attracted by gravity is an evolutionary skill. And it kind of is - life is not made out of photons. However, it's a byproduct. And I don't think you can really argue that evolution made a new physical law - since it is a product of physical laws. If the physical laws didn't enable consciousness, it wouldn't exist.
    – Probably
    Jan 26 at 7:17
  • @Probably Your analogy is specious. Gravity arises as a consequence of physical laws (those of General Relativity). Qualia do not; there is no emergent description of qualia built on physical laws, no qualia equation to predict experimental results. Also, zombies do not have qualia so they would not sit down and discuss them as we are doing. These are tired and trivial old issues, you have my answer to the question you asked; if you don't like it, post your own. Jan 26 at 12:21

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