The Peripheral Mind, by István Aranyosi. New York, NY: Oxford University Press, 2013. Pp. xiv + 232.
H/b £40.54.
This book proposes and defends the unusual view that the mind is constituted not just by the brain, but
by the brain together with the spinal cord and the peripheral nervous system.
The PNS is the part of the nervous system of vertebrates that lies outside the brain and spinal cord,
and has the function of transmitting nerve impulses from the receptors located all over and inside
the body to the central nervous system (CNS) consisting of the spinal cord and the brain, and from
the CNS to the effectors, namely the skeletal and visceral muscles to be found in the body. (p. 1)
Thus, according to Aranyosi, visual experiences are typically constituted, in part, by activity in the retina
and the optic nerve. And experiences of pain are typically constituted, in part, by activity in A-delta fibers
and C fibers (nerves that detect damage and carry information about it from the periphery to the spinal
cord). I emphasize that the author thinks of experiences as constituted by activity in the PNS. He is not
merely endorsing the truistic thesis that experiences are caused by such activity. Aranoysi thinks of the
mind “as really present throughout the body rather than as merely containing a body-image or being
informed by the body.” (p. 10)
However things may stand in other cultures, few people influenced by contemporary neuroscience
have found ideas of this sort congenial. What reasons does the author have for recommending the view?
There are three.
First, it makes sense of the changes in phenomenology he experienced during a bout with a
neuropathic disorder that partially disabled his PNS. While suffering from this affliction, he experienced
his limbs and outer extremities as external to himself. Here, for example, is how he experienced his foot:
My impression was that the lower parts of my legs had become alien to me. It was the same
impression as when you have a heavy object attached to your ankle which makes your muscles’
flexion more difficult, except the heavy outer object was now my own foot. And to that extent it
ceased phenomenologically to feel like my own foot. My foot, or what used to be my own foot
before, has now become part of the external world; a piece of denervated, hence, alien flesh to be
dragged around. (p. 7)
While this sort of experience suggests the idea that the mind inhabits the extremities of the body, and
helps to make the idea vivid, it does not selectively confirm the idea, for reflection shows that we can
explain the changes in experience due to peripheral neuropathy in purely causal terms. We can suppose
that the changes in experience are caused by changes in PNS activity; we need not assume that the former
changes are literally constituted by the latter.
I find the other two arguments for Aranyosi’s view quite elusive. Roughly, the second argument
maintains that the view makes distinctive and important contributions to the solution of certain
philosophical problems, such as the mind-body problem, and the third argument is an attempt to convince
us that we will be faced with an intractable causal exclusion problem involving peripheral phenomena and
certain other necessary conditions of mental states unless we view the peripheral phenomena as
constitutive of mental states rather than causes of them.
Because he maintains that the mind encompasses more than the brain, Aranyosi’s position is in some
ways similar to semantic externalism and the extended mind hypothesis. According to semantic
externalism, concepts and propositional attitudes are partially individuated by informational relations to
objects and properties in the external world. The extended mind hypothesis claims that manipulations of
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external objects like pencils, notebooks, and maps are actual ingredients of cognitive processes like
thinking and remembering. Despite the obvious affinities, Aranyosi is at pains to distinguish his view
from these other ideas. After criticizing the main arguments of their advocates, he concludes that “the
mind extends [only] as far as the nervous system does, namely, to the fringes of the PNS.” (p. 95)
Here is Aranyosi’s canonical formulation of his main thesis, the peripheral mind hypothesis:
(PMH) Conscious mental states typically involved in sensory processes are partly constituted by
subprocesses occurring at the level of the PNS. (p. 22)
In thinking about this hypothesis, we should keep it in mind that the expression “sensory processes” is to
be understood expansively, so that it applies to perceptual processes generally, and not just to the
processes associated with bodily sensations. By the same token, the conscious mental states to which
(PMH) refers are meant to include a large range of sensory and perceptual experiences. In what follows, I
will use “s-experience” to signal that the intended domain is quite broad.
Now as I interpret it, (PMH) is not a claim about s-experiences of all phenomenological types, but only
about s-experiences of phenomenological types that count as typical. So, for example, while it is
concerned with all of the s-experiences that occur in the course of our ordinary perceptual interactions
with the world, it has nothing to say about exotic forms of s-experience, such as stray visual sensations in
subjects born without sight, which result from internal factors. I also interpret Aranyosi as presupposing
that if a type of s-experience counts as typical, then its instances are always accompanied by processes in
the PNS. Given these assumptions, (PMH) amounts to the following claim: if a type T of s-experiences is
one that counts as typical, then all of the instances of T are partially constituted by processes in the PNS.
Although the restriction to types of s-experience that are universally accompanied by peripheral
activity has a relatively low profile in the text, it is important to realize that Aranyosi is obliged to adopt
it. Otherwise his peripheralist metaphysics would commit him to an implausibly disjunctive account of
the metaphysical nature of experience. To see why, let T be a phenomenological type, and suppose that
while s-experiences of type T are sometimes accompanied by processes of type P in the PNS, they are not
accompanied by such processes on all occasions. Suppose further that s-experiences of type T are
accompanied by central processes of type C on all occasions. (It is clear that there are types of sexperience that meet this description. Thus, for example, while pains in the leg are generally accompanied
by processes in peripheral nerve fibers, they are sometimes caused by pathologies in the spinal cord.)
Now clearly, if Aranyosi were to claim that the experiences of type T that are accompanied by processes
of type P are partially constituted by those processes, he would have to provide a different account of the
metaphysical nature of the experiences of that type that are not accompanied by P-processes. More
specifically, he would be obliged to claim that while some T-experiences are constituted by complex
processes of type C+P, there are others that are exclusively constituted by processes of type C. It is clear,
I think, that any such disjunctivist account of the metaphysical nature of experiences of type T would be
less attractive than the simple view that all such experiences are constituted by processes of type C,
period. This problem can be avoided by restricting (PMH) so that it is concerned only with types of sexperience that always accompanied by activity in the PNS.
The reader may reasonably wonder, however, whether any such types exist. Let T be a
phenomenological type of s-experience that counts as typical – more specifically, let it be the type of
experience that occurs when one sees a red rose in daylight. In most cases, instances of T will be
accompanied by activity in the retina and the optic nerve. But instances of T might also occur in vivid
dreams and realistic hallucinations, and we can imagine scenarios on which they are induced in a brain in
a vat. Hence, even though experiences of type T are typical, they are not always accompanied by
peripheral activity. We encounter similar concerns phenomena if we focus on bodily sensations like pains
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rather than visual experiences. Pains are of course typically accompanied by processes in peripheral nerve
fibers. But this is not always the case. As we noticed a moment ago, some pains occur as the result of
pathological conditions in the spinal cord. Such pains can be phenomenologically indistinguishable from
pains that have normal causes. Further, phantom limb pains occur when most or even all of the relevant
peripheral nerves are missing. These considerations suggest that despite initial appearances to the
contrary, even if we think of (PMH) as restricted to types of s-experience that count as typical, it commits
us to an unacceptable disjunctivist account of experience.
Aranyosi is aware of these difficulties and takes steps to meet them. This part of his discussion
contains some persuasive arguments, but other lines of thought are much less successful. I will consider a
three of his replies.
The problem posed by dreams is made pressing by experimental data, due to Christof Koch, among
others, which indicate that dream experiences are not accompanied by activity in brain area V1. Now
clearly, if dream experiences are not accompanied by activity in V1, they are not accompanied by
peripheral activity either; for in normal subjects, peripheral activity leads inevitably to processes in V1.
Thus, it might be thought that dreams are counterexamples to (PMH). But Aranyosi wishes to maintain
that dreams are in a special category – they do not count as typical in the intended sense of the word. He
does not tell us why, but he would presumably support the claim by pointing to the many
phenomenological differences between dreams and the usual run of perceptual states. Since (PMH) is
concerned only with kinds of experience that count as typical, Aranyosi is able to claim that dream
experiences do not pose a threat to the view.
This reply may leave us with the sense that Aranyosi should have chosen some word other than
“typical” to restrict the scope of (PMH) (although phenomenologically different from perceptual
experiences, dreams are typical occurrences); but there is an underlying point that we should accept.
When faced with an apparent counterexample to (PMH), it is always possible to preserve the principle by
narrowing its scope. On the other hand, this way of dealing with problems has a downside. Aranyosi
claims that (PMH) provides us with leverage against the mind-body problem. This can hardly be true if
we have to remove large swaths of phenomenal consciousness from its domain.
I turn now to the discussion of phantom limb pain. As far as I can tell, Aronyosi’s main response to
this difficulty involves an unannounced but very significant change in his main thesis. He writes:
[C]ases like the phantom limb do not show that the PNS is not important, witness that total
deafferation (cutting off the afferent peripheral nerves from the neck down) makes the phantom
limb disappear. So it is not as if the phantom limb by itself shows that the PNS is disposable when
it comes to explaining and ontically basing the phenomenology. (pp. 142-3).
Contrary to what Aranyosi seems to be claiming, his (contestable) point about the effects of total
deafferation has no tendency to support the view that phantom limb pain cannot occur without PNS
activity. Deafferation occurs when the spinal cord is severed, not when the PNS is disabled. Thus, instead
of providing a defense of (PMH), the point at most provides a defense of the quite different claim that a
certain amount of spinal cord activity is required for the experience of pain.
I like some of the things that Aranyosi says about pain. Among other things, he is quite right to assign
considerable weight to the fact that we experience pain as located in the body. In my view, as in his, this
fact places a very substantial constraint on metaphysical theories of the nature of pain. But the fact can be
accommodated without supposing that the mind is distributed throughout the body. More specifically, it
can be accommodated by adopting a perceptualist theory of experiential awareness of pain and an account
of pain itself that identifies it with bodily disturbances. Instead of extending the mind to as to encompass
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the parts of the body where pain is located, which is Aranyosi’s preferred strategy, this combination of
views sustains the idea that mental phenomena are grounded exclusively in brain processes. In effect, it
accommodates the fact that pains have bodily locations by kicking them out of the mind, allowing only
experiences of pain to count as mental. (For discussion, see Hill, Meaning, Mind, and Knowledge
(Oxford, 2014).)
Although Aranyosi discusses objections that appeal to a brain in a vat at some length, his response
appears to boil down to the following line of thought:
Melzak and Wall pointed out that there is a conceptual connection between a nerve fiber type being
nociceptive and its being a pain-specialized fiber; that’s how these fibers actually get their identity
conditions. Yet, in our thought experiment with the BIV pain there is no stimulus that we can
properly consider as noxious (or thermal, or tactual, or whatever). For that you need a world, in the
sense of an extra-neural reality. (p. 64)
I find this passage (as well as the surrounding discussion) baffling. It seems quite true that there is a
conceptual connection between a nerve fiber’s being nociceptive and its having something to do with
pain; but I cannot see that this fact about concepts has any bearing on the question under consideration,
which is whether the BIV can experience pain despite lacking a PNS. Nor can I see why the processes in
the computer with which the BIV is connected should not count as an extra-neural reality. Unfortunately,
this passage is fairly typical of the writing in much of the book: there are a number of extended
discussions that read more like first drafts than finished products.
In concluding, I would like to return briefly to Aranyosi’s positive case for (PMH). Although I don’t
find it ultimately persuasive, I agree that the view receives a certain amount of support from
phenomenological considerations. It would, I think, be quite useful to continue Aranyosi’s project of
collecting relevant phenomenological facts and attempting to analyze them from different perspectives.
Consider, for example, the following bit of phenomenology from Ian McEwan’s Atonement (Random
House (2001)):
[Birony] brought her forefinger closer to her face and stared at it, urging it to move. It remained still
because she was pretending, she was not entirely serious, and because willing it to move, or being
about to move it, was not the same thing as actually moving it. And when she did crook it finally,
the action seemed to start in the finger itself, not in some part of her mind. (pp. 33-4)
There is something that is very right about Birony’s perceptions – something that is very right and also
very mysterious.
In my judgment, the book under review has serious problems; but Aranyosi deserves considerable
credit for drawing our attention to an interesting range of phenomena and offering a detailed explanation.
CHRISTOPHER S. HILL
Department of Philosophy
Brown University
Box 1918
Providence, RI 02912
USA
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