God Soul Mind Brain

machinery that computes the presence of awareness. It is a natural extension for the same machinery to compute that same awareness signal and use it when constructing a model of one’s own mind.

    It is probably incorrect to think of the social machinery as computing in isolation the single proposition, “I am aware of thing Y.” Instead that proposition is presumably part of a larger bundle of linked information, a model of yourself that includes a set of mental attributes assigned to a location in space. In this way when you ask yourself whether you are consciously aware of thing Y, you have access to a set of related information including, for example, that you are an intentional agent, that you are standing or sitting in a particular position in the room, that you have a particular emotional state, that you are consciously aware of a variety of other objects in addition to thing Y, and that your awareness, your subjective self, is located inside your head. All of this information is generated and linked such that there is probably no such thing as accessing one part of the model in isolation of the other parts. Perhaps it is for this reason that consciousness is so difficult to define precisely. It may be a large, miscellaneous set of linked information of which awareness of specific items is only one part.

Multiple personalities and bistable perception

    In vision there is a wonderful phenomenon called bistable perception. A popular example is the Necker cube. It is an ambiguous drawing, a simple line drawing of a cube. One moment it looks as if it is oriented one way, and the next moment it seems to switch and orient itself another way. The reason for the switching is that your visual system constructs two different perceptual models, both of them consistent with the raw data, and the two perceptual models compete with each other. Sometimes one gains ascendancy, suppressing the other; sometimes the competition reverses and the other gains ascendancy. Subtle cues, such as variations in line thickness, or the act of thinking about the cube one way, can bias the competition and cause one perceptual model to win out; but after a while, the other model temporarily wins the competition and the perception switches back. Bistable perception (or multistable perception in the case of three or more ways to see the same object) is relatively well understood at least in its general outlines; it is a neural competition 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