Consciousness and The Self
Joe Lau
Philosophy
HKU
Readings
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Nagel “Brain Bisection and the Unity of
Consciousness” on reserve in philosophy
dept main office.
Online lecture notes at :
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http://artsci.wustl.edu/~jprinz/cog33.htm
Consciousness
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What is consciousness?
Phenomenal consciousness
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Having sensations, perceptions and experiences.
“What-is-it-likeness”
Self-consciousness
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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”?
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Unity of consciousness
We tend to think that each of us has a
single mind, which is the self.
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Mental states, emotions and moral
responsibilities are assigned to this self.
Nagel thinks that this assumption comes
under challenge from experiments on splitbrain patients.
Split-brain experiments
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Our brains have two hemispheres (left and
right).
The two hemispheres are connected by a
bundle of nerve fibers known as the corpus
callosum.
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Information passes between the hemispheres through
these nerve cells.
Bisection of CC is sometimes carried out to treat
epilepsy.
What would happen?
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Not much in ordinary activities.
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Swimming, talking, dressing.
Seems like just one single self.
But in special experimental situations …
Optic chiasma
Left and Right
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Left Brain
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Language
Math calculation
Controls right side of
body
Receives visual
signals from right eye
only.
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Right Brain
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Visual and spatial
skills
Controls left side of
body
Receives visual signal
from left side only
An example
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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
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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?
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None of these
possibilities are
plausible. Don’t
know how to
count…
Nagel : five possibilities :
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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.
Against possibility #1
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One mind in left brain,
right brain an
automaton.
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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
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One mind in the left
brain, some mental
events but no mind in
the right brain.
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Same as before.
Activities due to the
right brain are just as
coherent and
complex as those due
to the left brain.
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Purposeful behavior
Process language
React emotionally
Against possibility #3
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Two minds, one in the
left and one in the
right.
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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
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One single mind
distributed over the
two halves.
Dissociated contents
in a single mind.
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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
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Normally just one
mind.
Splits during
experiment.
Merge into one
afterwards.
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Ad hoc.
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What causes the split?
No anatomical change
during experiment.
Patient exhibits
integration even
during experiment.
Nagel’s position
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Argument
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Dissociation incompatible with one mind.
Integration incompatible with two minds.
Implications
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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