Consciousness and The Self Joe Lau Philosophy HKU

Readings Nagel “Brain Bisection and the Unity of Consciousness” on reserve in philosophy dept main office. Online lecture notes at :

Consciousness What is consciousness? Phenomenal consciousness Having sensations, perceptions and experiences. “What-is-it-likeness” Self-consciousness Having a concept of the self and being able to use this concept in thinking about oneself. “I am happy.” “Something is behind me.”

But what is this “self”? Unity of consciousness We tend to think that each of us has a single mind, which is the self. Mental states, emotions and moral responsibilities are assigned to this self. Nagel thinks that this assumption comes under challenge from experiments on split- brain patients.

Split-brain experiments Our brains have two hemispheres (left and right). The two hemispheres are connected by a bundle of nerve fibers known as the corpus callosum. Information passes between the hemispheres through these nerve cells. Bisection of CC is sometimes carried out to treat epilepsy.

What would happen? Not much in ordinary activities. Swimming, talking, dressing. Seems like just one single self. But in special experimental situations …

Optic chiasma

Left and Right Left Brain Language Math calculation Controls right side of body Receives visual signals from right eye only. Right Brain Visual and spatial skills Controls left side of body Receives visual signal from left side only

An example Flash “pencil” on left screen. E : “Which word is it?” P : “Don’t know” E : “Pick up the object” (P’s left hand picks pencil.)

Another example Flash “pencil” on LS and “toothbrush” on RS. “Pick the object that is named.” Left hand would search for pencil, and right hand would search for toothbrush.

How many minds? Nagel : five possibilities : One mind in left brain, unconscious automaton in right brain. One mind in left brain, some mental events in the right, not not enough for a mind. Two minds, one can talk and the other can’t. One mind with dissociated contents. Normally one mind, splits during experiments and combine into one afterwards. None of these possibilities are plausible. Don’t know how to count…

Against possibility #1 One mind in left brain, right brain an automaton. Argument 1 : “what the right hemisphere can do is too elaborate, too intentionally, directed and too psychologically intelligible” to be an unconscious automaton.

Against possibility #2 One mind in the left brain, some mental events but no mind in the right brain. Same as before. Activities due to the right brain are just as coherent and complex as those due to the left brain. Purposeful behavior Process language React emotionally

Against possibility #3 Two minds, one in the left and one in the right. But the patient’s behavior is tightly integrated and coherent in normal situations. Unified decisions and reactions with no evidence of dissociation in normal circumstances.

Against possibility #4 One single mind distributed over the two halves. Dissociated contents in a single mind. But a single mind should be unified, and it is not. We cannot imagine incompatible intentions and experiences in a single mind.

Against possibility #5 Normally just one mind. Splits during experiment. Merge into one afterwards. Ad hoc. What causes the split? No anatomical change during experiment. Patient exhibits integration even during experiment.

Nagel’s position Argument Dissociation incompatible with one mind. Integration incompatible with two minds. Implications Impossible to decide how many minds they have. Mental states do not require unified mind. Perhaps we are like split brain patients in normal situations. Maybe the idea of a self, a unified mind, is unscientific; it is an illusion that does not explain anything.

Sperry's tachistoscopic display