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Richard Cytowic's book The Man Who Tasted Shapes may be purchased
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Synesthesia - A Real Phenomenon? Or Real Phenomena?
Luciano da F. Costa
Cybernetic Vision Research Group
IFSC - University of Sao Paulo
Caixa Postal 369
Sao Carlos, SP, 13560-970
BRAZIL
luciano@ifqsc.sc.usp.br
Copyright (c) Luciano da F. Costa 1996
PSYCHE, 2(10), 2(26), January 1996
http://psyche.cs.monash.edu.au/v2/psyche-2-26-dacosta.html
KEYWORDS: synesthesia, cross-modal associations, consciousness, emotions.
COMMENTARY ON: Cytowic, R. E. (1995) Synesthesia: Phenomenology and Neuropsychology.
PSYCHE, 2(10).
ABSTRACT: This text comments on Cytowic's recent review on the current knowledge
on synesthesia. Recent neurophysiological findings are discussed that suggest
cross-modal interference in the mammalian brain. Based on these results,
it is proposed that synesthesia may not be restricted to the phenomenologically
characterized abnormality described in Cytowic's review, but rather that
it may encompass a series of related physical phenomena in the brain. Some
additional remarks on the relationship between emotions and consciousness
have also been included.
1. Introduction
1.1 Cytowic's review presents a survey about the current knowledge on synesthesia
(joint perception). A number of interesting points are discussed that bear
direct implications for consciousness studies, especially the phenomenon
of cross-modal interference and the usually neglected role that emotions
may have over our actions. Although I have little doubt that inter-modal
interference actually takes place in the human brain, I believe that the
precise characterization of synesthesia as a neurological abnormality is
not completely clear, at least in the way in which it was reviewed in Cytowic's
article. On the contrary, it seems that synesthesia is a much more generalized
effect that may take place throughout a range of scales in the brain. The
implications of cross-modal association are particularly important with
respect to the everlasting riddle of qualia. This review ellaborates on
these issues. Some comments have also been included regarding the relationship
between emotions on consciousness.
2. Synesthesia - When Phenomenology is not Enough
2.1 The principal problem with synesthesia is that it has been almost exclusively
characterized in phenomenological terms. The very features considered for
its diagnosis, as described in section 4 of Cytowic's review, rely heavily
on phenomenological evidence which, of course, is subjective. There is no
doubt that as such, i.e. without cogent physiological or anatomical substantiation,
synesthesia is destined to be treated with understandable scientific caution.
I am not fully acquainted with the statistical data gathered by Cytovic
and other researchers, but even if thousands of documented cases were available,
that would not be enough to qualify synesthesia as a real physical phenomenon.
It should be stressed at the outset that this does not necessarily mean
dismissing synesthesia as a real phenomenon, but rather that more substatial
physical evidence is needed. If not, based on thousands of reports, we should
take for granted that UFOs have been visiting earth and abducting people.
2.2 Would that mean that synesthesia is destined to remain an elusive concept?
The surprising answer is no! For, although overlooked in Cytowic's review,
there is new neurophysiological evidence strongly supporting the fact that
cross-modal associations do take place in the mammalian brain. In one experiment
described in Rauschecker (1995), portions of the anterior ectosylvian cortex
typically dedicated to vision (AEV) became responsive to auditive and somatosensory
input as a consequence of cortical plasticity responses to visual deprivation
in cats. Such a phenomenon implies not only improved accuracy for analysis
of auditory and somatosensory information, but also raises the hypothesis
that part of the auditory (or somatosensory) stimuli can be "seen"
by some individuals with specific lesions or developmental abnormalities.
Similar results have also been reported respectively to monkeys and humans
(PET and ERP were used in the latter case). Based on such findings, it seems
that cross-talk between different modalities can indeed be produced by rewired
afferent connections. It is also possible that cross-modal interferences
are present even in the normal cortex, though their diminished scale prevents
them of being clearly perceived.
2.3 It is important to point out that such neurophysiological evidence was
obtained from a neocortical region, not the hippocampus as suggested by
Cytowic. In fact, given the distributed functional organization of the brain,
it would be hardly surprising that cross-talk between modalities does take
place. Thus, it seems we could have many manifestations of synesthesia throughout
most of the brain, not just the kind of synesthesia described in Cytowic's
review. This leaves us with some interesting implications. Firstly, it would
be expected that blind people are more susceptible to synesthesia. Secondly,
the hypothesis that qualia perception is localized in the brain would be
substantiated.
3. Emotions, Qualia And Consciousness
3.1 The proposal that the hippocampus possesses a key role in synesthesia
motivated Cytowic to discuss emotions. Although I do agree with his position
that the limbic system has received little attention, I question his hypothesis
that the limbic system dominates the neocortex. I also believe his two clinical
examples used to support such a thesis are mistaken, for: (i) low threshold
does not entails dominance (the fact that we are highly susceptible to cardiac
malfunctions does not mean that the heart rules over the brain) and (ii)
the sequence of events that are experienced by those emerging from coma
seems in fact to provide a counter-example for Cytowic's thesis, for the
individual has to wait for the neocortex to dominate the rest of the brain
before consciousness is recovered. The question about which part of the
brain rules seem to me to transcend our current knowledge about the brain
workings and be related to controversial issues such as whether consciousness
is distributed or localized.
3.2 Be that as it may, the interplay between emotions and consciousness
is undoubtedly an interesting issue. The reasons why emotions are important
for consciousness includes: (i) they play a major role in determining our
actions; and (ii) they are closely related to the elusive concept of qualia.
It should be observed that emotions have been so difficult to scrutinize
because they are associated with large scale brain processes. More precisely,
emotions are to a large extent governed by biochemical processes, such as
the release of specific neurotransmitters and enzymatic processes (see Black
1994), which influence great portions of the brain. The close relationship
between emotions and qualia consists of another important topic deserving
more attention.
4. Concluding Remarks
4.1 Cytowic's review provides some interesting insights about cross-modal
associations. The characterization of synesthesia as a well defined phenomenon
is however elusive, since it relies on subjective phenomenological evidences.
New neurophysiological findings, which are briefly outlined in the present
text, provide more substantial evidence supporting the possibility that
cross-modality interference may be a real and even fairly common feature
of the brain. Such results are however related to cortical regions and not
the hippocampus as proposed by Cytowic, which indicates that synesthesia
can be a much more generalized phenomenon. Some of the views expressed in
the original review regarding emotions have also been commented upon.
References
Black, I. B. (1994) Information in the brain. The MIT Press.
Chalmers, D. J. Towards a theory of consciousness. PhD Thesis, Indiana
University, USA.
Cytowic, R. E. Synesthesia: phenomenology and neuropsychology - A review
of current knowledge. PSYCHE, 2(10).
Flanagan, O. (1992) Consciousness reconsidered. The MIT Press.
Rauschecker, J. P. (1995) Compensatory plasticity and sensory substitution
in the cerebral cortex. TINS, 18(1), 36-43.
