The central part of the transmigration argument focuses around a small set of one or possibly more neurons or other small set of brain matter being replaced with something like a silicone isomorph that behaves the same, perhaps through transducers, in stimulating any downstream motor neurons leading to the picking the strawberry. It is usually proposed that the original isn't completely replaced, but rather simply configured with the silicon isomorph in such a way that it is easy to repeatedly swap between which one is engaged in the system.
The conclusion drawn is that since, by definition, the silicone isomorph is stimulating any causally downstream neurons in an indistinguishable way, it must also result in the same phenomenal awareness somehow necessarily 'arising'. But, there are several types of possible theories, including the Nature Has Phenomenal Properties
theory for which this is not necessarily true.
To see how this theory could work, consider that the set of neurons, or whatever, being replaced has a red phenomenal quality - in additional to any behavioral properties that cause and effect observation can detect. This particular spot of phenomenal red is being used by our brain as a voxel (3D pixel element) to represent a corresponding spot on the surface of the strawberry. This set of neurons is configured in the rest of our brain in a way that this voxel of phenomenal red is, due to whatever phenomenal laws of nature might be, unified together with all the other similar sets of neurons representing the rest of the voxels in a unified 3D space representing a strawberry patch we are looking at.
This theory predicts It is this unified 3d representation, and the difference between the phenomenal red representing the strawberry at one spatial location and the phenomenal green representing the leaves at another, that is our awareness of the location of the strawberry amongst the leaves. And it is this conscious phenomenal knowledge that enables the downstream mechanism to choose to pick it and initiate the actions to move the arm to do just that.
The theory predicts that any intended switchable substitution set of circuits, composed of silicone or anything else, that would result in identical functionality of the entire system, must then have and be able to present a similar phenomenal property for this same voxel into this unified phenomenal model of this strawberry patch that is our knowledge, before any equivalent awareness of such would be possible, and before any downstream functioning neurons could function similarly in the picking of the strawberry.
It could be that only a particular set of specific kind of brain matter in a particular active state has a red phenomenal property, and a different set has a green phenomenal property representing the leaves. This could also include that silicone, nor anything else that is drastically different in its fundamental nature, has anything like these same phenomenal properties. Because of this, it could not recreate and present the same phenomenal spot of red into the unified system of conscious knowledge, making it impossible for any downstream behavior to be identical.
We should point out that these phenomenal properties are properties of the same brain matter that has the behavioral properties traditional scientific cause and effect observation can see. Behaviorally, we can see everything they are doing, including what downstream neurons they are stimulating, and so on. But, just like knowing that the surface of the strawberry has a causal behavioral property such that it reflects 700 NM (red) light, tells us nothing of any phenomenal quality the same surface may or may not have. In other words, if we cut open the brain of whoever is experiencing this red, and shined a light on whatever gray matter has this red phenomenal property being used to represent conscious knowledge, it would surely be more likely to reflect grey light, or something other than 700 nm light. Phenomenal properties are in this way blind to mere traditional cause and effect observation and require effing of the ineffable to be demonstrably understood.
When we use our cause and effect based detectors, it is true that we can identically model all such behavior, including equivalent stimulation of causally downstream neurons. But you must also include the fact that a theoretical model that only includes discreet stimulation of downstream neurons through synapses, does not, alone, resolve the 'binding problem' where everything is unified into one world of conscious awareness. There must be some additional physical behavior that must be modeled, which achieves this unification of awareness. The Smythies-Carr Hypothesis
is one of many possible theories that includes a natural behavior which could accomplish such binding.
The nature of our conscious knowledge includes introspective subjective knowledge of the phenomenal nature of what is doing the representation. When we are tasting salt, we can imagine throwing a switch in someone else's mind, enabling them to experience the same thing, and thereby effing what salt tastes like to us, to the other person. Any mechanical isomorph system must include similar knowledge, if it is indeed expected to behave the same, especially when it is asked such a question as: "What is red like for you?".
We can easily make a 'zombie' robot that knows about the strawberries and the leaves, by representing red with an abstract 1, and green with an abstract 0. Though such abstract knowledge could enable the system to be intelligent enough to behave the same as far as picking the strawberry, it, alone, would certainly not act the same if we asked it what its red was like.
Another possibility is you might be able to have some kind of introspective abstract knowledge about your abstract knowledge in the design. In other words, the silicon isomorph could include knowledge of the fact that it represents red with one and green with zero. When you asked it what it was like, it could reproduce the behavior by mapping this awareness from one and zero - to words and attempted descriptions of red and green. In other words, you could program such a system to lie about 'what it was consciously like'. But of course, if you were able to eff the ineffable, and fully understood how it's mind worked, you would easily know its similar behavior was nothing but a lie.
So, in conclusion, we believe that to assume that just because a silicone isomorph to a neuron is behaving similar by simply stimulating it's causally downstream neurons in a way that does not include some additional mechanism to achieve binding of conscious awareness is somehow resulting in subjective consciousness arising from any functionally equivalent isomorph, is taking things way too far. And we see that the 'hard problem' likely isn't as 'hard' as initially thought.
We believe the transmigration argument can be seen as a fallacious one.