"The emphasis on action and adaptation is closely connected to the assertion that there is intrinsic affect in sensation. Affect can incite action (a tendency to approach or avoid), but it is unclear how awareness alone or a mere registering of a thing without evaluation, could result in adaptive behavior." (Wayne Viney, Charles Hartshorne's philosophy and psychology of sensation, In: The Philosophy of Charles Hartshorne, The Library of Living Philosophers, Volume XX, Lewis Edwin Hahn (Ed.), LaSalle, IL: Open Court, pg. 105, 1991.)
I. A New Somatic Sensory Neuroscience
A. Introduction. The old view of somatic sensory neuroscience is that the neurons of the brain generate "representations" of objects in the external world <1>, which - when the neurons are electrically active - the mind somehow perceives. The utility of the notion of representations for the identist (mind = neural activity) point of view is obvious. If neuronal activity "represents" (in the sense of 'making a copy of') the world and if that same activity "is" the mind, then one can justifiably claim that the mind-body problem is close to being solved: by knowing our neurons we know (a representation of) the world. This gives us, however, as Santayana said, "solipsism of the present moment," where each of us is completely alone, encased within our own skull, contemplating our neuronal representations without any notion of past or future. Furthermore, the hard problems - of how neuronal electrical activity leads to conscious awareness and why the matter that makes up neurons in certain parts of the brain allows awareness to occur whereas no other kind of matter does the same - remain unsolved.
The new view proposes that the somatic sensory system "represents" (in the sense of 'making clear') for the mind the-body-in-contact-with-the-world. This view accepts that everything is interconnected at the level of quantum nonlocality (nonsensory perception; Hartshorne's "affective continuum," see <6>) and that having a nervous system allows us to become consciously aware of those aspects of the world toward which we have intention, regard, or concern, i.e., which afford us opportunities for action. In this view, there is no need for the brain to represent (create an image of) the world since we already "know" it - we are literally part of it - at a preconscious level. It seems to me that this process philosophical approach also solves what I call the "representation problem." This problem is an empirical one, namely, as will be briefly described below, that there are no neurons in the brain that can be said to actually represent (stand for) the world or its objects, at least not in any way that is discernable to a human observer monitoring their activity. I should add, for the sake of completeness, that even though the process philosophical approach appears to solve the "representation problem," there still remains a pretty hard problem of why and how neuronal electrical activity is necessary for embodied human consciousness. I suspect we will make more progress on that issue once we abandon the mistaken notion that the role of neuronal electrical activity is to generate internal representations of things.
B. The features of receptive fields of somatic
sensory neurons support the idea that neuronal activity signals prehensions.
Each neuron in the somatic sensory system has a receptive field (RF) and
is active (firing action potentials) when we handle, or are touched by,
or imagine (for neurons > 1st order) handling an object that contacts the
The fact that these neurons in the putamen, a part of the brain not noted for its contributions to conscious sensory awareness, were recorded in an unconscious (anesthetized) monkey raises some questions. I would argue (and will do so in more detail later, in conjunction with the motor system lectures) that these neurons are part of a process that signals potential, not actual, conscious events. The total set of such neurons and their sensitivities will define the motorsensory horizon, just what aspects of the world and its objects any particular creature will potentially be able to perceive and take action toward. When the animal makes an action decison (which presumably would not be possible for an anesthetized animal), the experience of a subset of such neurons, and the neurons in other parts of the somatic sensory system with which they are in prehensive relation, will be bound together and an agent, taking action in the world blossoms into an occasion of conscious awarenss.
II. Solving the "binding problem" seems to require neuronal prehension. Neuralists claim to circumvent the "representation problem," but in so doing seem to invoke the idea of neuronal prehension without knowing it. They argue that, while it is true that no neuron uniquely represents anything, the response of the whole population of neurons, each of which vaguely represents one or another stimulus feature, contains very specific information. "Population codes" or "distributed codes," they say, uniquely represent each and every stimulus. This gives rise to the "binding problem," namely how is the activity of spatially separate, not anatomically interconnected neurons that represent one or another stimulus feature brought together, or integrated (bound up), into a knowing of a whole object? In short, how is the information encoded in the population assessed? The answer, according to the neuralists, is to be found in synchronous neural firing. When spatially separate neurons fire action potentials at nearly (within ~ 1 msec) the same time, their information is, somehow, unified into a whole percept. Esther Gardner and Eric Kandel, near the end of their chapter on "Touch" in Principles of Neural Science describe the situation as follows:
"How does the brain put together all of these features to form a coherent percept of an object? The firing patterns of neurons in separate cortical areas interact in ways we do fully not understand. The problem of binding together activity in different regions of the cerebral cortex has been studied more extensively for vision than for touch. Those studies of the visual system indicate that the brain may bind together the various stimulus features by synchronizing firing in different cortical areas." (pg. 468)Now please make no mistake about two well-established empirical facts: Population responses do contain very specific information and synchronous neural firing is widespread in the brain (not just the cortex) during conscious perception<4>. Those facts are not an issue. The issue is how synchronous neural firing causes binding. From the neuralist perspective, saying that "neurons that fire together represent together" seems like a magical explanation, somewhat equivalent to a statement like, "Well, that is just the way the mind works; it can pick and choose which neurons it wants to pay attention to." In contrast, from a process philosophical perspective, the ubiquitous presence of synchoronouly firing neurons in the brain during conscious awareness fits right in. That is, prehensive networks of neurons, whose electromagnetic oscillations are to establish the content of conscious awarenss from an embodied perspective, fire synchonously. By definition, the information content of a prehensive neural network is bound! Thus, from a process philosophical perspective it appears that there is no such thing as a "binding problem."
III. Body Schema. A similar process is going
on all the time with the body via proprioception. In fact,
our somatic sensory perceptual system prehends (many of) the cells of the
body and it is only because of this "feeling of feeling" of the cells of
our own body that we are able to come to know our own body in the world.
This is what accounts for our so-called "body schema" (an illusion of 'folk empiricism') and
the posterior parietal/superior temporal lobes of the right hemisphere seems to be
particularly important in this
regard. There is suggestive evidence <5> that supports the idea
that the right infereior parietal/superior temporal cortex is especially important for
non-sensory processing. See "Prehensive Networks and Conscious Awareness" for
further considerations of the idea of body schema.
See Anosognosia for Hemiplegia for a recent attempt to use the notion of two varieties of perception to explain a mysterious condition that seems to involve a loss of one half of the body schema. This condition sometimes follows a right hemisphere stroke that involves the parietal lobe. The anosognosic patient denies that he or she is paralyzed and neglects stimuli to the left side of the body.
IV. The Locus of Somatic Sensory Awareness.
What is true for somatic sensation is probably true for the other senses.
The senses share a common logic of operation: objects that have been prehended
and which afford an opportunity for action blossom into sensory perception.
For compound individuals with nervous systems, the locus of conscious perceptual
awareness is, of course, the dominant occasion of experience, also known
as "the mind." Unfortunately, the ease with which 'mind,' as the
experiential, i.e., "mental" capability of the dominant occasion of experience,
can be abbreviated or circumscribed (reified) into a thing-like entitiy
inhabiting ordinary bits of the world as they are known to us via sensory
perception causes enormous problems. The neural dependence of embodied
conscious awareness compounds these problems. Together, these snares
are likely to lead astray those who are not wary of the "fallacy of misplaced
concreteness," causing them to fall prey to the mistaken notion that mind
is simply "in" the brain or "in" the activity of certain neocortical neurons.
This is a very hard belief to eliminate in part because it seems so commonsensical,
after all, the substantiality of matter is a fact of daily experience and
consciousness depends on brain activity. Another reason it is a hard
belief to give up is that it is partly true – mind is "in" the brain,
in the sense that we are beholden to properly working brains for the content
of our embodied consciousness. Nevertheless, such a point of view
is far from the complete picture. Mind is, in fact, a distributed
function of brain, body, and world: it is as correct to say that mind is
"in" the body, or "in" the world, as it is to say that it is "in" the brain.
V. Notes and References
1. Consider, for example, this section heading in the Chapter on "Touch" by Esther Gardner and Eric Kandel in the Principles of Neural Science, 4th Ed.:
"The Body-Surface is Represented in the Brain by the Somatotopic Arrangement of Sensory Inputs." (Italics added.)Or take Pashler's description of the sensationist approach:
"The core idea of the information-processing approach is to analyze the mind in terms of different subsystems that form, retain, and transmit representations of the world. The nature of these subsystems, the kinds of transformations they carry out, and the temporal relationship and relative discreteness (or nondiscreteness) of their activities are all viewed as facts to be discovered, not assumed at the outset. Obviously, one cannot say in advance whether or not the mind can be successfully analyzed in these terms." Harold E. Pashler, The Psychology of Attention, Cambrige, MA: The MIT Press, pg. 7, 1998.Or take another example from Principles of Neural Science:
"Our sensory systems form internal representations of our bodies and the external world. One of the principle functions of these internal representations is to guide movement. Even a simple task such as reaching for a glass of water requires visual information to establish an internal representation of the location of the glass in space. It also requires proprioceptive information to form an internal representation of the body so that appropriate motor commands can be sent to the arm... [For voluntary movement t]he task of the motor systems is to reverse the task of the sensory system. Sensory processing generates an internal representation of the world or the state of the body, but motor processing begins with an internal representation, namely the desired result of movement." Principles of Neural Science, 4th Ed., (Kandel et al, Eds), New York: McGraw-Hill, pgs. 651 & 658, 2000.
2. Asanuma, H., Stoney, S.D., Jr., and C. Abzug, Relationship between afferent input and motor outflow in cat motorsensory cortex. J. Neurophysiol. 31:670-681,1968.
3. Graziano, M.S.S. and C.G. Gross, A bimodal map of space: somatosensory receptive fields in the macaque putamen with corresponding visual receptive fields, Exp. Brain. Res. 97:96-109, 1993.
4. For example, see Llinas, R. and D. Pare, The brain as a closed system modulated by the senses, In: The Brain-Mind Continuum: Sensory Processes, Cambridge, MA: The MIT Press, pgs. 1-18, 1996; Nicolelis et al, Simultaneous encoding of tactile information by three primate cortical areas, Nat. Neurosci. 1:621-630, 1998.
5. Deouell, L.Y., Bentin, S., and N. Soroker, Electrophysiological evidence for an early (pre-attentive) information processing deficit in patients with right hemisphere damage and unilateral neglect, Brain 123: 353-65, 2000. See also Karnath, Hans-Otto, New insights into the function of the superior temporal cortex, Nature Revs. Neurosci. 2: 568-76, 2001.
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