This description seems to place psychotic experiences on a spectrum with normal experiences, with the psychotic ones ‘more’ explicit and ‘more’ external. In other words, psychotic experiences differ from normal experiences in degree, not in kind.
I don’t think I am on board with this. If you claim that the -contents- of the thoughts are not radically different from normal thoughts, then fine, I agree. But a key component of many psychotic experiences seems to be attributing the cause of the thought or action to something external to oneself. As in, the experience of witnessing your arm rise up in the air, compared with the normal experience of lifting your arm on purpose. And the idea that normal experiences are simply experienced as ‘less’ external than psychotic experiences, does not seem to be supported. It seems more suitable to describe these experiences as differing in kind from normal experiences.
When I look at my carpet and then move my eyes up to look at the ceiling, things move rapidly in front of me. And yet, I do not witness the world in turbulence. Probably, when the signals are sent to my eye muscles, a corresponding signal will be sent to another part of my brain, warning me to take account of the incoming movement, thereby preventing me from perceiving turbulence. This is described as corollary discharge, (or self-monitoring), and failure of corollary discharge is a possible way of thinking about some psychotic experiences. A failure of someone’s brain to appropriately announce incoming subvocalisations could cause the person to experience the speech or thought as coming from elsewhere; failure to announce arm movement could cause perceptions of involuntary movement, and so on.
Maybe you were familiar with these ideas already. But the point is, if corollary discharge failure is a fruitful way of thinking about psychotic experiences, which I think it seems to be, then I don’t think it makes sense to describe psychotic experiences as simply ‘more’ external than normal experiences. The thoughts may be similar to normal ones in terms of their content, but the way they are experienced is qualitatively different. If your self-monitoring system failed once, you might chalk it up as just a freaky occurrence. But if it kept happening, it would surely begin to cause a lot of distress, and you might start to feel that you were being controlled. It is noteworthy, then, that this mechanistic account of psychotic experiences is consistent with the success of early-intervention treatments of psychotic conditions.
This way of thinking about involuntary thoughts or actions is supported by some experimental evidence. I think it also tallies with the recent(ish) discovery that future actions are decided in the brain before one is conscious of them. I read about it in ‘Schizophrenia: A Very Short Introduction’, chapter 7 - ‘Understanding the symptoms of schizophrenia’. More evidence and discussion is presented in the more psychiatry-sceptical volume ‘Models of Madness’, chapter 16 - ‘Understanding Psychotic Symptoms’ (PM me if you are interested in either of these ebooks).
