Susan J. Blackmore
Department of Psychology, University of the West of England, St
Matthias College, Bristol BS16 2JP, United Kingdom.sjb_ac@hotmail.com
http://www.uwe.ac.uk/fas/staff/sb/index.htm
Abstract: The sensorimotor theory of vision is the best
attempt yet to ex-plain visual consciousness without implying a
Cartesian theatre. I suggest three experiments which might test the
theory.
If we were thinking clearly about consciousness we should surely
have crossed James’s (1890) "fathomless abyss" by now, but
we have not. I agree with Dennett (1991) that the root cause of our
confusion is the seductive lure of the Cartesian theatre (CT) (that
mythical place where consciousness happens; that imaginary container
of the "contents of consciousness." Most existing theories
– though their proponents deny it – entail some form of Cartesian
theatre. Global workspace models do so, as do most current at-tempts
to find the neural correlates of consciousness. Put at its simplest
(and perhaps most extreme) we can say this. Ask the question
"what is in my consciousness now?" (Or "what is in x’s
consciousness at time t?"). If you believe there is an answer
then you are imagining a Cartesian theatre.
O’Regan & Noë (O&N) provide the best attempt yet to
escape from the clutches of the CT. Their theory is exactly the kind
of bold departure that is needed. But is their theory right? And do
they go far enough?
O&N suggest that "it is not possible to subject a general
frame-work to direct verification." However, I think some of
their central claims can be tested and I offer here three suggestions
for doing so. These are not easy tests to perform but I hope they may
reveal how different are the predictions of this theory compared with
other, more traditional, theories of vision and visual aware-ness.
1. Scrambled vision. Traditional experiments using inverting
goggles show that people gradually learn to see the world "the
right way up," but during the learning phase they suffer two
competing views, as described by O&N. We might imagine that in
some way they gradually learn to invert their mental picture of the
world. In the proposed experiment people would wear goggles that
completely scrambled the visual input (this scrambling might also
include blind spots, bars, or other gaps without affecting the
argument). If O&N are correct, the new sensorimotor contingencies
should be no more difficult to learn than with a simple inversion, but
this time the subjects would effectively begin their learning blind.
Their visual input would appear as noise and they would see nothing
meaningful at all. As they learn the new contingencies by visual
manipulation they would gradually come to see again. This new seeing
would, if the theory is correct, be experienced as just like ordinary
seeing. I would love to know what it is like to learn to see and would
happily volunteer for such an experiment.
2. Manual vision. The feelings associated with facial vision in the
blind might, in the spirit of O&N’s theory, occur because the
sensorimotor contingencies of the face and ears are linked. That is,
moving the ears necessitates moving the face. In this experiment
auditory feedback is provided while subjects try to detect virtual
objects in front of them by manually controlling the position of
virtual ears. They could then move their faces independently of moving
their "ears." In this case the theory predicts that they
would feel things not on their faces but on their hands.
3. Blinded vision. Phenomena such as habituation and stabilised
retinal images usually prompt only the conclusion that the visual
system needs changing input to function. O&N, in contrast, propose
that active manipulation of sensorimotor contingencies is required.
This difference could be tested by yoking pairs of subjects together
in the following way. ‘A’ subjects are able to move their eyes
normally and explore a visual scene. ‘B’ subjects are given
exactly the same changing visual input but their own eye movements are
ineffective and uncorrelated with the input they receive. O&N’s
theory makes the strong prediction that ‘A’ subjects will see
normally, but ‘B’ subjects – while receiving identical visual
input – will be blind.
These tests, especially the last, might help find out whether
O&N’s bold theory really holds or not. If it does they will have
made a huge step towards eliminating the CT since in their theory
seeing is a way of acting, not a way of building up unified
representations of the world – or pictures in the CT. And
incidentally (though they do not mention this), it may also explain
the currently mysterious profusion of descending fibers in the visual
system.
Nevertheless, their attempt is not, I suggest, completely
consistent. For example, they claim (in sect. 2.6) that visual
awareness requires not only mastery of the relevant sensorimotor
contingencies but integration of this with thought and action
guidance. There are possible counter-examples in both directions.
First, fast actions that are controlled by the ventral stream are not
normally reported as conscious (Milner & Goodale 1995) yet they
should surely count as "action-guidance." This step is
particularly odd since they helpfully point out problems with Milner
and Goodale’s analysis in section 8.5.3. Second, experience in
meditation suggests that it is possible to stop all thought, planning,
and overt action (if not sensorimotor manipulation) without losing
vision.
Finally, a few subtle hints of the CT remain – showing just how
hard it is to escape altogether. Such phrases as "features of the
car enter consciousness" or "are available in
consciousness" (sect. 6.2) imply a CT, as do the claims that some
sensorimotor contingencies are "accessible to awareness," or
are "brought into conscious-ness" (sect. 6.6). And there
seems to be some confusion in the way they compare their views with
Dennett’s. While claiming that "qualia are an illusion"
(sect. 6.3) and "the conception of phenomenal consciousness
itself must be. . . rejected" (sect. 6.9), they nonetheless take
Dennett to task for being "insufficiently attentive to the actual
phenomenology of experience" (sect. 7.3). Yet, as Dennett
famously says: "the actual phenomenology? There is no such
thing" (Dennett 1991, p. 365).
Building a theory that does justice to the reality of consciousness
without invoking a CT is extremely hard. I think O&N, in spite of
these small problems, have come closer than anyone else. Their theory
is bold, testable, and a rare step in the right direction.
