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Sensation, Intelligence and Brain Activity

Thoughts on Sensation, Intelligence, and Brain Activity
Can our knowledge be reduced to brain activity?
Dcn D. McManaman
First, let me emphasize the real distinction between sensation and intelligence. Since, however, sensation is more
evidently intertwined with matter, I would like explore this mode of knowing first; for if we can appreciate the
immateriality involved in sensation, appreciating the immateriality in intellectual knowledge will be much easier.
The first point is that sensation is an activity. This is such a significant point. The reason is that if sensation is an
activity, it involves an agent, a single substance or being. It is an agent who sees, who hears, who touches, who tastes,
who imagines and who remembers, etc. I, who am a single being, perceive. It is not my eyes that see, rather, I see by
means of the sense organ. So too, it is not my ears that hear, rather, I hear by means of the end organ of the ear drum.
But of course, it is not merely the end organ (i.e., the eye). “Organ” also refers to the cortical center of the brain, and also
to their connecting link (i.e., the optic nerve). Also, by extension, it is not my brain that perceives, nor is it my brain that
is aware. I am aware, and I sense by means of the organ of the brain. The brain is a part of me.
Now, the agent who is able to sense (which is an activity) is, logically, the kind of agent who has the potentiality to
sense, or the power to sense, i.e, to see. I have the power to see. So, sense organs are not enough. There is both power
and organ. The reason is that an activity is an “act” or actualization, and actualization means that a capacity or
potentiality is reduced to actuality (or act or activity). Activity is the realization of a potentiality. The agent is the first act
(for there is no seeing without a seer, just as there is no running without a runner). But “activity”, such as that of seeing,
is called “second act”. Between first and second act is the power or potentiality to activity (that is, the power to see, taste,
touch, imagine, etc).
A camera is a mechanism, but it is not a single agent that sees. A camera does not see, it does not perceive. There is no
activity, just passivity (something happens to it). In fact, when we use a camera, the camera is simply an extension of our
own activity, that is, it is an instrument of our own activity. But sensation is an activity of a single agent, a single being
that has the power to see. Thus, sensation is rooted in a psychosomatic composite (a substance that is a matter/form
unity). A sense cannot function without both a power and an organ, and so any damage to an organ will interfere or even
destroy the ability of the sense to operate. A plant does not see or touch (the Venus fly trap does not feel), it does not
have the power to see, or touch, or taste, or hear. Sensation is a vital act, an immanent act of a living thing, not an
inanimate act of an inanimate substance. For example, rusting is not a vital act, burning is not a vital act, causing
moisture is not a vital act; but sensation is a vital act (an immanent act), an act of a living thing or living being. Sensation
is an agent’s awareness of a singular material thing that is other than the agent, a material singular that is outside the
Now, there is a passive element to sensation; there has to be. Something has to move the power from potency to activity,
and the object of sensation is a material singular, so it is going to be a material thing that acts upon the senses. So in
sensation, what occurs is that the sense organ is acted upon (passivity), and the agent senses (acts) by means of the organ.
Because sensible things are actually sensible, they can be immediately sensed by a sense power. To be sensed, they need
only impinge upon a sense power, since a sensible thing is already (actually) sensible in itself, and so there is no need for
an active power to render or reduce it to the state of being actually sensible. So, although man requires an agent intellect
to reduce what is potentially intelligible to being actually intelligible, there is no “agent sense”.
The senses must be acted upon if they are to know, as color must act upon the eyes if I am to see, and as compression
waves must act upon the ears if I am to hear. So, the senses are passive powers, faculties or potencies—faculties or
potencies are known, they are not seen or perceived. Hence, the senses must be moved to activity. The eye, as well as
any other sense, when passive (before it senses), is not determined. The senses, then, when not actually sensing, are
indifferent as to what they are to report. The eye is indeterminate or indifferent as to what color it will see (of course, it is
not the eyes that see, but I see by means of the organ). To say that the organ is indifferent is to maintain that it is in itself
indeterminate or unspecified, and therefore, to know one definite object, the sense must be determined or specified.
That which specifies the sense is called a “sensible species”. Thus, the reason I see a tree and not a dog or a cat is because
the object known (the tree) specifies my act of knowing. This sensible species is produced by the extramental object
acting upon the sense organ. Moreover, since every effect somehow resembles its cause, the sensible species (the effect)
carries the nature of its producing cause (the physical object). This species carries the nature of the physical object
because the species is produced by that object: it is emitted by the object. A sensible species is a physical radiation
emanating from the sensible thing (without it, my senses would not be moved to act). This species is a precursor of
sensation; it is not a sensation floating through space searching for a cognitive agent. As a vital act, sensation is
immanent: it is in the knower. As a precursor to sense knowledge, the species itself is not known.
Inasmuch as knowing is an activity, what must be explained is the transition to this activity. Prior to the activity, the
senses are not active but passive. It remains passive until awakened by an external object, until it receives a species or a
determinant from that object. It is only upon reception of this determinant that the act of sensation takes place. After
having been activated by the species, the sense performs its act of sensation. This is knowledge.
Yet our knowledge is a knowledge of things, not the sensible species. If it were a knowledge of the species, or what is
happening within us, or what is happening to our sense organs, then to perceive is not to perceive things, but our own self,
or some aspect of our self. We would not know things, we would not know the sensible world, but only what is in us.
And if that were the case, we would not even know that we don’t know the sensible world but only ourselves, and we
wouldn’t even be able to distinguish between an optical illusion and a normal perception that is non illusory. Thus, when
a person argues that we can’t know whether or not there is an extramental world, or that optical illusions prove that our
senses are unreliable, they show the opposite, in fact.
Now, what requires further elaboration is how an external thing can, by arousing the senses, become an object of
A machine is not an agent who acts. A machine can be acted upon, but there is no transition from being acted upon to
acting. The machine is not perceiving, because the machine is not a single being, not a single agent with the power to see,
or touch, or imagine, or desire, etc.
To study the biochemistry of sense perception is to study this passive aspect of sensation. But the scientific study of
this passive aspect of sensation involves sensation on the part of the one doing the studying (the scientist)--the scientist
must be perceiving (acting, activity). He is studying one side of it, the side that he’s unaware of as an ordinary
sensing creature in the act of perceiving—we’re all unaware of that aspect. But to study the passive aspect of sensation
is not the same thing as studying sensation (which is a study involving reflection and reasoning), and much less is it
the same thing as the actual awareness involved in the act of sensation—we’re all aware of ourselves sensing (thanks
to the central sense, or synthetic sense), but few of us are familiar with the biochemistry of the eye and what occurs when
one sees. A strict study of the passive aspects, that is, the biochemical conditions of sense perception, without knowing
sensation from within, would not provide us with a knowledge of the activity of sensation—we wouldn’t know what it
means to sense. That can only be known from within. I know that I perceive, that I sense, that I see, that I taste, etc.
And so the one cannot be reduced to the other. The one is related to the other, the one is a necessary condition for the
other, but not a sufficient condition. In other words, sense perception cannot be reduced to neuro biochemistry. To
reduce it to that is to destroy it, to eliminate it.
That is why a mechanistic approach (reductionistic materialism) cannot account for sensation. Only a psychosomatic
anthropology can account for it. You are a psychosomatic unity (a matter/form unity), you are a multiplicity insofar as
you are a material and quantified thing (i.e., with many parts), but you are a unity insofar as you are a being, an acting
agent (one is a property of being, for whatever is, is one).
Now the word ‘object’ is derived from two words: ob: towards, and jacio: to throw. An object projects itself or emanates
a likeness of itself towards a subject, which emanation is the species or determinant that impinges upon the external
senses. This emitted determinant, by impressing itself upon the senses, activates the recipient power from its state of nonsensing
to sensing.
G. J. Gumerman writes: “All materials at temperatures above absolute zero in the natural environment produce
electromagnetic radiation in the form of waves. The electromagnetic spectrum is a continuum of natural and induced
radiation in wavelengths varying from fractions of a micrometer to kilometers”. (Gumerman and Lyons, Science, April 9,
1971. P. 126.). Every object produces its own specific radiation. Now, at this moment there are, in the room you are in,
sound and color waves of which you are unaware, because you are not properly attuned to receive them. You can verify
this by simply turning on a radio or television set. These devices (mechanisms) are able to catch and register the
impinging waves. Similarly, an object is radiating its likeness. Such emanations from the object hit all surrounding
things (desks, chairs, walls, people, etc.) Just as radio or TV waves can be picked up only by a proper receiver, so
likewise only cognitive beings can catch the emitted determinants*. How these determinants travel from the object to
the knower is as difficult to explain as the picture on the TV screen. The sensible species comes from the physical object,
thus it is a received species; and to say it is received is to state that it impresses itself upon the sense: it is an impressed
species. It is the function of the determinant to unite knower with known, to make the external object present to
the sense organ or power. What I perceive when I am in the act of perceiving something is not the species, but the
material thing outside me.
That is what is so mysterious about knowledge (sense knowledge and more so, intellectual or conceptual knowledge).
The determinant (sensible species) unites knower with the known. The sensible species is a formal sign whose sole
function is to signify. It is purely intentional. If it were not, our sense knowledge would be at best indirect knowledge. I
wouldn’t know things, but the sensible species, and then I’d have to somehow deduce that it was the result of some cause
that has a likeness to it. But then we are back to square one, and we now have to explain how I know the sensible species,
i.e., by means of another species?
An “object” (according to the etymology of the word) is that which is presented to a subject (thrown at). You are a single
subject, which is why we can speak of an object of sensation: subject and object are correlative terms. But a machine,
like a computer, is not a subject (it does not have a subjectivity). It is purely and completely an object. It can be the
subject of a change, for example, it can begin to rust. But it is not aware of an object, much less aware of its awareness.
At best, a machine becomes an instrument of a living perceiving subject, the one who is using it to take a picture. We
designed the machine, so there is a sense in which we project a kind of subjectivity into it (it is made after the likeness of
the producer, it is an instrument designed to memorialize a moment in time), but there is no subject if there is no single
being. Only a single, knowing, entity, a cognitive being, can be a subject of knowledge, because only a knower has an
object of knowledge. Moreover, each sense has a formal object: the formal object of the sense of sight is color, the formal
or immediate object of the sense of taste is flavor, the formal object of the tactile sense is the pressure or resistance of
external things, the formal object of the temperature sense is relative warmth or coldness of objects, the formal object of
the kinesthetic sense is pressure within the body, etc. An object can only exist for a subject. Without a subject, there is no
object of knowledge, no object as such, only existents (beings or things). They become objects (in the strict sense of objacio)
when a subject enters into the picture.
Now, in the act of sense perception, a knowing subject is modified in a way that can be studied by science. For example,
his sense organs are modified in some way, there is neurological changes in certain parts of his brain, his retina becomes
colored, etc. But when a scientist takes it upon himself to study the biochemistry involved in sense perception, there is an
ordinary, pre-scientific mode of knowing that includes self-knowledge—this is such an important point. Now this selfknowledge,
which involves an intellect capable of complete self-reflection, is a pre-scientific mode of knowing that is
perpetually self-conscious or entirely reflective (i.e., I know that I am knowing, I know that I am sensing, I know that I
am seeing, I know that I am touching, that I am moving, that I am breathing, I know that I am, that I am one, and that my
self-consciousness extends as far as my extremities, for I know that I am not the molecules and atoms in the immediate
atmosphere surrounding my hands, feet, face, body, etc). This pre-scientific knowledge governs the scientific process
from within, so that at each moment, I (the scientist) know what I am studying, for I know that I am coming to
understand the neurological conditions of sense perception and that sense perception is a cognitive act of a knowing
being or subject. If I didn’t have that pre-scientific knowledge, I wouldn’t know what I am doing in studying the
neurological conditions of sense perception. My study would lack a framework and a focus.
It is this that sheds light on the immaterial aspect of sense knowledge. Sense knowledge is not and cannot be entirely
material. Sensation in the human person always involves intellection, which includes complete self-reflection (I know
that I am seeing, I know that I am touching, etc). Now, a material organ is not capable of total self-reflection; for no
material thing is capable of total self-reflection. The reason is that a material thing has parts, and so reflection in a
material thing is only partial: one part can reflect upon another part (but the whole does not reflect upon the whole). Take
a piece of paper and fold it, for example. One part will be folded upon another, or reflected upon another. But a single
part cannot entirely reflect upon itself. The instant a part is made to reflect, it is lifted off and away from where it was
previously. So too, a mirror (which is a material thing) only reflects partially. Now the sense of sight cannot reflect upon
itself, because the sense of sight involves a material organ. The sense of sight does not see itself in the act of seeing, nor
can I touch my sense of touch touching. But I am capable of complete self-reflection, for I know that I am knowing.
Moreover, I know that I am sensing (I know that I am seeing, tasting, hearing, etc). I as a whole, a single being, am aware
of myself as a whole. I am aware of my thinking and sensing. That is the self-reflection of a single being that is
indivisible and conscious of that indivisibility (I know that I am one being). It follows that my mind is immaterial, it is
simple and has no parts.
The same cannot be said of the sense organ. The brain is not immaterial, nor is any organ of sensation, which is why the
sense organ does not reflect upon the whole of itself—no sense can sense itself sensing. Nor do I imagine my imagination
imagining. The brain is the organ of internal sensation, and as a material organ, it too cannot engage in complete or
“whole” self-reflection, only partial self-reflection.
Sensation in the brute animal which lacks intelligence and thus lacks the capacity of complete self-reflection, is still
partially immaterial. In other words, sensation in the brute animal is not an entirely material process. It is the activity of
an agent (a psychosomatic unity). It cannot be reduced to the objectivity of neural biochemistry—in sensation, there is a
transition from passivity to activity, and the animal knows something outside itself without changing what it knows (there
is no chemical reaction or chemical change, the organ is specified, but it is not changed or transformed into a different
thing). The animal is aware of something outside of him.
Knowledge per se is not a change. Indeed, physical changes accompany knowledge (sense and intellectual). All human
knowing implies a physical change, because it is linked to sense perception. But although all knowledge is accompanied
by a physical change (my finger immersed in warm water becomes physically warm), this change does not constitute
knowledge. A thermometer also becomes hot if immersed in hot water, yet there is no knowledge in the thermometer. So
too, the camera receives an impression of the object being photographed, yet there is no knowledge. Sensation involves
change, but change is not knowledge. To be physically heated is not to sense heat. In seeing, there is a physical
alteration in the organs: there is a contraction or dilation of the senses, and chemical processes occur in the rods and
cones. In plant life, in order to become something other than itself, a plant must cease being itself (i.e., a tree becomes a
wooden desk by first ceasing to be a living tree). In cognitive life, however, the knower becomes the known without
ceasing to be. Knowledge opens up the subject, enabling him to become “intentionally” what he cannot become
physically. Knowledge is not a physical becoming, but an intentional becoming. It is an immaterial becoming, even in
the brute animal. An immaterial power of a psychosomatic unity is actualized—even though this actualization is
inextricably linked to the changes in a sense organ. Without losing his physical identity, a cognitive being shares in the
perfections of other things. In sensation, the perfections it shares are not as profound as the perfections shared in
intellection—the animal only perceives the accidental modes of being of things (i.e., color, flavor, size, temperature,
pressure, etc). There is a much richer apprehension in intellectual knowledge.
The brute animal is aware that it is sensing through the central sense (or synthetic sense), which is an internal sense that
unifies the separate data received from each external sense, composing the data into a single percept (internal sensible
species), so that the animal knows (sense knowledge) that what it smells, touches, and tastes, and sees, all belong to the
same single object (i.e., the single apple or the meat, etc).
There is simply no way that the sense activity of a single agent can be understood reductionistically or mechanistically.
The reason is that to reduce a substance to a collection of substances, to a multiplicity, is to destroy the unity, or better yet,
it is to forget the unity, to overlook it, that is, to have one’s head so immersed in the multiplicity of the molecular or
subatomic realm that one loses awareness of the initial knowledge of the thing, the initial apprehension of what this thing
is, and the existential judgment “that it is” (and is one). When that is lost, one must account for sensation as an activity of
a single substance or entity, but one cannot do that unless one knows that single substance. Sensation is not a passivity of
some accidentally unified “thing” (as if “thing” or “substance” is merely some kind of illusion, as the reductionist
Now, the intelligible species is another thing altogether. The intelligible content of a thing, the idea, the concept
conceived within the mind, is of an entirely different nature. At least a percept can be remembered, and when it is
remembered, one is aware that it is an image, a sensible image, a particular, one that corresponds to the thing in reality.
When I imagine John Smith, that image is a remembered percept that corresponds vaguely to his appearance when he
came to see me a couple of weeks ago, and when he was in my class last year. But an intelligible species is altogether
different. It is not an image, but a meaning. Simple or complex ideas have no image, they are not sensible. Take the idea
“complex”—it is not a sensible; it does not look like anything at all. It is an intelligible idea. Consider the idea of
metaphor, or the concept “analogy”, or the complex idea “a metaphor is not an analogy”. The idea “analogy” does not
bear upon any particular analogous relationship, but covers them all. Most importantly, the apprehension of existence
(being)—, which is not to be confused with the general idea of being—is not an image, it is not sensible, but it is the most
intelligible aspect of things—before I sense a being’s color, and before I apprehend “what that thing is” (its essence), I
apprehend “that it is”. The act of existence (esse) cannot even be made into a concept. I can have a concept of John
Smith (i.e., he is human), but I apprehend his existence at the same time, and the apprehension of an act of existing is
neither a sense perception nor the apprehension of a thing’s essence—it is an apprehension “that you are”.
Being cannot be made into a concept, for to do so is to make it a genus. Recall that the specific difference is always
outside the genus (rational is outside the concept animal, otherwise all animals would be rational), but the only thing
outside of being is non-being, which is nothing. So being cannot be a genus, it is not a logical entity like an idea. Being
or existence (esse) is an act, and you and I have the ability to apprehend that act. But that is not an image, it is not a
sensible. I cannot hear existence, I cannot see existence. I hear sounds of existing things (birds), I see the colors of
existing things, and my mind gradually apprehends the nature of the things I perceive through intellectual abstraction, but
I judge (apprehend) the very existence of the thing that is colored, moving, smooth and cold, etc.
The brain is active while I am thinking, because my thinking is always accompanied by sense impressions, sense
memories, perceptions, internal images of words, etc. Although being is not an image, my imagination provides one
nonetheless, such as the very image of the word ‘being’. But concepts are not extended, they are not mutable, nor are they
divisible (they are indivisible), etc. But once again, it is a single agent that knows, that conceives ideas, who understands
the diverse natures of things (partially, imperfectly, to be sure), the interrelations between things, who perceives the
motions of things but also understands the meaning of those motions (I perceive a moving thing, but I also understand that
this motion is a person running for his life, or diving to win gold, or building to shelter his family, etc). And so even
motions are particular and universal; there is this motion here, and motion in general, like the motion of “chemical
The problem with reductionism is that it is a knowledge issue. It’s not about science, it is about knowledge
(epistemology). There is an epistemological error buried in reductionism. It is rooted in a lack of awareness of the role of
knowledge in the scientific process, in particular the role of pre-scientific knowledge.
A reductionistic method of producing knowledge of the constituent parts of a whole does not yield a knowledge of this
unity that you possess from within, ordinarily and pre-scientifically—you know yourself as one being. It only yields
knowledge of a plurality (a multiplicity of parts). And you understand the plant or your pet cat, etc., as a single whole
precisely because you know yourself as a single whole. You and I correctly interpret an animal’s writhing in pain because
we know pain’s reality from within, and we project this knowledge into the animal when we see it acting in a similar way
to our own experience. Without that interior knowledge, writhing in pain would appear to be a kind of geometric folding
and contorting. In the same way, you know yourself as an extended substance (through external and internal sense
perception), but you also know yourself as a single entity, that is, as one being—and you know this through selfconsciousness,
and you become conscious of yourself when you know something outside yourself. That is part of the
reason why you know things as unified things or beings. You know that apple as a single thing, that it is distinct and not
continuous with the atmosphere around it or the table below it. Although the animal might not be aware of its own
awareness (that requires an immaterial intellect that is capable of complete self-reflection, not just the central sense), and
thus might not be aware of its own awareness of its state of pain, (but only aware of its pain), you understand that this
animal is in a lot of pain. In the same way, it is this experience of your own interiority, this experience of yourself from
within as a single and indivisible whole that allows you to understand that the cells in this frog, or in this man, are parts of
the single being (whole) that is this frog or man.
So it is not reductionism that can account for self-consciousness, it is self-consciousness that renders the reductionistic
method of doing science possible. That’s what reductionism is, a method. It is not a metaphysics. It is not a philosophy
of reality. When Arthur Eddington, for example, said that solidity is an illusion, that it is not real, because this table is
made up of atoms that are mostly empty space, he was substituting ordinary pre-scientific knowledge with a knowledge
derived from a method. It was a knowledge issue at the root of that absurd claim. But test his hypothesis; throw a brick at
him and watch how quickly he gets out of the way. Why? He knows that brick is solid. Solidity is a property that
belongs to things, and we know things ordinarily, and that ordinary pre-scientific knowledge is not illusion. If it were, so
too is the knowledge derived from a scientific method; for there is only one faculty of knowing, and if it is defective and
unreliable on the initial level, it is unreliable on all subsequent levels.
Without the self-consciousness of your own radical unity, you could not know “parts” to be what they are, namely “parts
of a whole”, and thus you would never come to know a being (a thing). Again, although one cannot lose a sense of this
self-consciousness and continue doing science, one can indeed never come to an explicit awareness of the role this
self-consciousness plays in rendering an empiriometric and reductionistic method possible and fruitful.
* The word “determinant” is a perfect word to use here. Note the etymology of the word: de term or de limit. To
determine is to “terminate” or end. Something which has a term has an end; it is finite. A motion that terminates is a
motion that comes to an end. Now, when treating motion or change, we studied the four causes (agent, formal, material,
and final). The final cause is the end or term. A motion comes to its end when the form (formal cause) is achieve, that is,
when the motion is perfected (made through). A determinant determines, that is, specifies, or informs. What radiates
from the object determines or specifies the organ. It informs it. Knowledge, whether it is sense knowledge or intellectual
knowledge, is about being “informed”, that is, it is about the power (sense or intellect) becoming specified (sensible
species or intelligible species).
Copyright © 2012 by Douglas P. McManaman
All Rights Reserved

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