- seCtIon tWo: tHe BRAIn
problem head on. We should try and find the neural correlates that correspond
to what we’re conscious of ’ (in Blackmore, 2005, p. 69). He explained that he is
looking for the correlates of the ‘vivid representation in our brains of the scene
directly before us’ (Crick, 1994, p. 207). Until his death in 2004, he worked closely
with Christof Koch to find ‘the minimal neuronal events jointly sufficient for a spe-
cific conscious percept’ (Koch, 2004, p. 104). So, rather than looking for the NCs
of consciousness in general, they were looking for NCs of particular experiences.
Crick says that they chose vision ‘because humans are very visual animals and
our visual awareness is especially vivid and rich in information’ (Crick, 1997, p.
21). Also, visual inputs are relatively easy to control, we have detailed knowledge
of the primate visual system, and that of higher primates is similar to our own. In
some ways it is regrettable that vision has been studied in so much more depth
than other senses, but it has a crucial place in the search for the NCCs. So, in this
section we extend the discussion of the previous chapter to delve further into the
neuroscience of vision. Note, however, that much research in this area assumes
rich mental representations underlying visual experience, an assumption which
Chapter 3 showed to be questionable.
At the start of their endeavour Crick said, ‘so far we can locate no single region
in which the neural activity corresponds exactly to the vivid picture of the world
we see in front of our eyes’ (1994, p. 159), but he knew what he was looking for –
something which corresponds to that ‘vivid picture’. He and Koch laid out their
working hypotheses as a ‘framework for consciousness’ (2003). They proposed the
front of the brain as a kind of unconscious homunculus observing the sensory
areas, with many ‘zombie’ modes of processing all over the brain, consisting of
transient coalitions of neurons corresponding to representations of thoughts,
images, and perceptions. This idea of coalitions or neural assemblies goes back
more than half a century to Donald Hebb (1949), but has been transformed by a
better understanding of how large collections of neurons can work together. Crick
and Koch proposed that these constantly changing coalitions compete with each
other, attention biasing their competition. In vision, the neural activity travels fast
up the hierarchy to frontal cortex, providing a conscious gist of the scene, and
then travels more slowly back down the hierarchy to fill in the details. Recalling
the picture-in-the-head theories discussed in Chapter 3, Crick and Koch proposed
that conscious vision is like a series of snapshots with motion ‘painted’ on.
With this framework in place, they tried to find the NCCs. ‘First you want an idea of
whether it’s that set of cells firing, or whether they fire in a special way, or whether
it’s a combination of the two, or something else quite different’ (in Blackmore,
2005, p. 70). Crick was referring here to the different possible ways of thinking
about the NCCs – as a place, as a specific group of neurons, or as a particular
pattern of cell firing. The problem here is that if some processing is conscious
and some is not, what is the ‘magic difference’? Do some cells have a special extra
ingredient? Are some patterns of firing able to ‘create’ or ‘give rise to’ subjective
experiences, while others cannot? Does connecting cells up in a special way, or in
certain sized groups, make consciousness happen in those cells but not in others?
Put like this, none of the options sound very plausible. If you’re looking for the
NCCs, by definition you believe in the hard problem, but it often seems that
instead of solving it you merely end up suggesting that it applies to some brain
areas or processes and not others. Yet this does not deter researchers from
‘the minimal
neuronal events and
mechanisms jointly
sufficient for a specific
conscious percept’
(Koch, 2004, p. 104)
‘so far we can locate no
single region in which
the neural activity
corresponds exactly to
the vivid picture of the
world we see in front of
our eyes’
(Crick, 1994, p. 159)