Why do we believe in phenomenal unification?

In the last two posts, I introduced the idea of phenomenal unification and raised the question about how we know about it, if in fact it exists. In this post, I will put forward one proposal about what leads us to believe in the existence of phenomenal unification. I won't come down one way or the other on whether this justifies us in our belief in phenomenal unification, because I do know not if what I propose explains our belief in phenomenal unification would simultaneously also be sufficient to produce phenomenal unification. If this proposal is right and phenomenal unification goes beyond what I say here, I suspect that we should be highly skeptical about whether any of our experiences are actually unified.

Here is my proposal: two features of an experience are unified when we are not able to attend to them separately. When we try to attend to one, we automatically attend to the other as well.

Suppose that attention works as follows. The cerebral cortex is able to modulate activity in sensory regions of the brain. It encourages certain neurons -- such as those associated with a particular sense, or a particular part of the visual field, or with a particular object, to become more active. They start activating more easily in response to less clear stimuli. Their activity in turn allows them to contribute more forcefully to higher level centers (such as memory).

According to the proposal, groups of neurons that separately represent different features of an object might get linked together. When this happens, any modulation in the activity of one automatically gets carried over to the other. As a result, when one tries to pay attention to one feature, one not only encourages activity in the part of the brain responsible for registering that feature, but one also encourages activity in any linked areas. When we pay attention to one feature, not only does it contribute more forcefully to our memories and other higher faculties, but so do any linked areas.

Why is this a plausible explanation of our belief in phenomenal unification? Well, phenomenal unification clearly involves the inseparability of the two unified features of our experience.  The inseparability involved in phenomenal unification means that we cannot think of one without the other, we cannot picture one without the other, we cannot focus on one without the other. The model put forward provides a explanation of these features. We can't think about one without the other because doing so would require devoting attention to it. As soon as we devote attention to it, it follows that we attend to the other as well, and consequently, that we think also of it. We can't think about color without shape, because we cannot help but attend to an object's shape when we attend to its color.

If this rough model is even vaguely right, what does it say about phenomenal unification? It suggests a rather mundane neurological explanation for our belief. If there is something special about unified experiences over and above their functional effects, then this explanation doesn't capture it. And so if this explanation of our beliefs is correct, we should doubt whether our experiences really are unified in a deeper sense.