Chapter
Five
The theatre
with consciousness. Crick and Koch hedge their bets
by referring to ‘[t]he (unconscious?) homunculus’.
Perhaps all we can safely say about mental rotation
is that distributed processing in various areas of the
cortex somehow gives rise to the solutions to rota-
tion problems, and either gives rise to or at least
correlates with the experience of watching a mental
rotation and being able to describe it.
Another example may help. Look around until you
find something blue to look at, perhaps a piece of
clothing or furniture, or a book or coffee mug. Or
close your eyes and imagine a blue cat. Now ask,
what is this blueness and where is the blueness
located? We know in some detail how colour infor-
mation is processed in the human brain, and that it
must, in some sense, be responsible for the experi-
ence of seeing blue. But how?
This is, once again, a version of the hard problem –
how does the subjective experience of blueness
arise out of all these objective goings-on? An answer
that does not work is that the incoming information
is turned into a blue picture on a full-colour mental
screen for us to look at. There is no single time and
place where colour happens. Colour information is
distributed through the visual system and used in
multiple parallel versions by different brain areas.
Even if there were an inner picture, for example in
the form of the retinotopic mapping in V1, what
would make it blue when all neurons are similar
to each other and operate entirely in the dark? As
Dennett points out, there couldn’t be blue pigment
in the brain, so could it be figment? Of course not.
The central mystery is what makes this experience
of mine feel so undeniably blue. We cannot solve
it by positing a mental screen covered with colour
figments and looked at by an inner self. So how can
we solve it?
THEATRES THAT ARE NOT
CARTESIAN?
The problem that tempts us into imagining a Car-
tesian theatre is that it seems obvious that we are
aware of some of our actions but not others; con-
scious of some perceptions and not others; have
access to some of our desires but not others. So, we
have to wonder – what makes the ‘magic difference’?
seeInG BLUe
How do we see blue? And why does blue
appear the way it does? one problem for
consciousness lies in understanding how an
experience of seeing blue is related to neu-
ral activity in the brain. It may help to think
about how colour processing works.
there are three types of receptor in the
retina (somewhat misleadingly called
red, green, and blue cones) that respond
differentially to different wavelengths of
light hitting them. output from the red and
green receptors is subtracted to produce one
dimension of colour and summed to produce
a luminance signal (which then contributes
to other kinds of visual processing). this sum
is subtracted from the output from the blue
cones to produce a second colour dimen-
sion. these two-colour opponent processing
signals are sent (as rates of neural firing) via the optic
nerve to the thalamus and then to the visual cortex. In
the visual cortex, some areas use only luminance infor-
mation and construct edges, movement, and other visual
features, while some also use the colour information and
incorporate it into processing visual scenes and perceived
objects. output from this processing is then used in fur-
ther brain areas dealing with associations, memory, and
the coordination of behaviours. so, when you look at a
blue mug, neurons throughout the visual system are fir-
ing at a different rate or in different patterns from how
they would fire if the mug were orange.
But where does the experience of blue happen? Where
are the qualia? Where or when, in all this processing, does
the conscious experience occur? theories of consciousness
must either:
1 Answer the question, for example by proposing a
brain area, a special kind of processing, or a fea-
ture of functional organisation that is responsible for
consciousness.
or
2 explain why there is no answer.C
on
C
e
P
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5.1