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between alternative perceptual models.

    If the social machinery of the brain constructs a perceptual model of the self, and if this perceptual model is consciousness, then a very strange prediction ensues. Under some circumstances, it aught to be possible for the social machinery to construct two or more competing models of the self. These models should exhibit the classical properties of multistable perception: in competing with each other, they should alternate. At times one model should be ascendant, and at times another model should win the competition. The sudden switching from one state to another might occur randomly or might be triggered by subtle cues that bias the system. This bizarre prediction follows from the theory that consciousness is perception—social perception—applied to oneself. The prediction rather closely resembles the clinical descriptions of multiple personality disorder (also called dissociative identity disorder).

    White Eve was the gentle, timid wife. Black Eve was uninhibited and emotionally unstable. Jane was the sensible one. All three personalities existed in the mind of one woman, and at any moment one or another one was in control. The more-or-less true story of The Three Faces of Eve (the film was released in 1957) caused a surge of public interest in the multiple personality disorder. The syndrome is so bizarre and so difficult to confirm objectively that it is still somewhat controversial. Do some patients fake it? Are the symptoms implanted in their imaginations accidentally by the suggestions of a careless therapist?

    In certain ways the multiple personality disorder is only an exaggeration of the normal. We all act differently in different contexts. For example, most of us have a work persona and a relaxed-among-friends persona. (For some people these contrasts are rather striking.) What makes the multiple personality syndrome so strange and so alarming is not so much that there is more than one way of behaving, but that consciousness itself is partitioned among them. White Eve, for example, knew nothing about Black Eve. She was not conscious of anything Black Eve thought or did.

    I am arguably venturing onto shaky ground here, since the disorder is controversial. It is easy to dismiss the sensational claims as pseudoscience. But I think it is possible to understand how such a thing could in principle exist more or less as it is described. Normally the social machinery builds perceptual models of other people’s minds. A model of a mind contains a vast, linked set of information on personality, on goals, on intentions, on agendas. It also contains information on the contents of the person’s awareness. The nature of the model is that it is internally linked—it is “associative”—meaning that when one part of it is accessed, the rest comes too. The model is the means by which we understand the other person’s mind. The social machinery also builds a perceptual model of the self. What is to stop it from building more than one perceptual model of the self, each with its own personality, each with its own information on the contents of conscious awareness? When you are asked whether you are consciously aware of A or B or C, if you have multiple self models, your answer will depend on which self model is searched. How such a disorder—having one’s social machinery create more than one self model—could possibly develop in the first place is a separate question of the life history of the patient. Nobody knows the answer to that question. But once we understand consciousness to be a perceptual model, it follows that the machinery could in principle support multiple competing models that alternate due to the process of multistable perception.

Boxes and arrows

    I drew a diagram to try to get across the main point.

    Diagram 4-1

    Biology is messy, and a simple diagram is never truly accurate. As I explain the various parts of this diagram, the scientist in me will point out