Seeing red

[emjay]

This is how I see it; just as neural visual processing happens in layers, I think visual perception also happens in layers. A way to visualise it would be as transparencies laid on top of each other. The bottom one, the input layer - call it L1 (and note these L's here are just to demonstrate a point and bear no relation to the actual structure of the visual cortex) - would just be a photograph of a visual scene. Then above that would be L2, a layer mapping and representing colour information. L1 would be said to 'project' to L2. But as a transparency, this layer placed on top of L1 would look exactly the same... they would be seamlessly integrated perceptually because L2 would be extracting one property from the raw data in L1. Then say you've got L3 mapping lines. L1 would project to L3 but L2 wouldn't so diagrammed hierarchically L2 and L3 would be on level 2 and L1 would on level 1. Again, L3 as a transparency placed on top of the other two would be seamlessly integrated. Then on top of this you have the output layer - L4. All of these layers would be interconnected bidirectionally so that allows for both bottom-up and top-down activation and pattern completion.

So if you look at dreaming, the input layer, L1, is essentially turned off because your eyes are closed and you are not receiving visual input. Yet you can still dream vivid visual dreams. That makes sense if layers L2 and L3 are activated from the top-down by L4. The perception, having the bottom transparency removed, still captures the general structure of the photograph but loses the fine-grained detail of the raw data. For the sake of this, L4 can be considered the focus layer in that it is a map of the visual field just like L1 except that in receiving projections from L2 and L3 it is used to associate those object features. So by activating a neuron in L4 it would bidirectionally - and bidirectional connectivity is a prevalent feature of the visual cortex and most of the cerebral cortex - activate the associated neurons in L2 and L3 or bias them for easier activation from L1... that is to say, if the threshold value for firing a neuron is say 50 then bidirectional input reduces that effective threshold, so that say a value of 40 from L1 would be push it over threshold. That is neural bias. Anyway, the focus layer would receive input from whatever drives focus in the system... so that would be the feedback loop you talk about between environment and motor output.

Now if you take the question of imagination (and memory), I think this theory offers a good explanation. I think imagination is when there is a mismatch between the layers L1 to L4. That is to say if L2 and L3 are activated to simply extract the features of L1 then perceptually they seamlessly integrate because of the transparency effect I've described. But if a different set of neurons was activated in L2 and L3 - which could well happen not just because of top-down bidirectional input from the focus layer but also from any other areas of the brain that project to any of these layers - say a green pixel where the underlying data represents a red pixel then there would be a vague show-through effect and the greater the 'erroneous' activation of the L2 and L3 neurons, the more their transparencies would interfere with the perception of L1. So imagination starts off vague... just a kind of ghostly outline/sense superimposed on the visual field... but as it grows stronger it becomes more and more vivid. And this also I think could explain what I mentioned earlier in that you lose visual awareness when you get lost in thought; there would come a point when the interference from the erroneous L2 and L3 activations would essentially block L1 from having any say in the activations in L2 and L3, and thus visual perception would now fully reflect the context activated from the top-down... for the duration of this, until you snapped out of it, L1 would essentially be 'talking to the hand'.

And I think this transparency/interference principle would apply equally well to the other sensory modalities and their equivalent transparencies. And the integration of it all into a unified whole would still reflect the same principles, just at a much more complex level of interconnectivity. And whatever's 'in focus' in consciousness at a given time would reflect where the activation is concentrated in these layers, in the constant interplay of top-down, bottom-up, and lateral connectivity and influence. In other words focus to me is a passive thing... it follows where and how the network settles and reflects it.

Thank you for describing your model to me.  That does make a lot of sense.   I can't help but feel though that it is missing a command center where the output of these stages is registered.  Maybe if I had more experience with neural nets, but maybe not.

I think the connectivity of the network would account for everything - ie no need whatsoever for 'software' in the brain just neural network dynamics playing out according to specific patterns of connectivity and the feedback provided by the living organism interacting with the environment. But if that connectivity includes binding neurons for the different perceptual systems, who knows. That could be what the claustrum was for the consciousness switch we talked about earlier, but I don't know. I think it would be natural for such representations to form, given the right connectivity, and perhaps such connectivity is preserved through DNA to create such structure in future generations, but I wouldn't so much think it would be a command centre as an association centre. So it could be that the different perceptions are coordinated from a specific brain area, but I think only in terms of associations and using the same neural network principles as everywhere else. But still with the same net result that whatever is actively represented in the network is also mirrored in consciousness, not just in terms of what - ie the neural representations - but also the manner and timing of when it is perceived (regardless of what form that perception takes... what form the qualia takes). In other words ignoring the form of the qualia, the representational content we experience in consciousness appears and disappears, and qualitatively becomes more vivid or more vague, in exactly the same manner and timing as a would be expected of the equivalent representations in a neural network activating or deactivating according to the network dynamics. I can't ignore that so Occam's Razor to me says that qualia mirrors what is actively represented in the network at any given time.