Noûs, 39(2): 197–255,
June 2005.
Cognitive Architecture, Concepts, and Introspection:
An Information-Theoretic Solution to
the Problem of Phenomenal Consciousness
|
Murat
Aydede University
of Florida Department
of Philosophy 330
Griffin-Floyd Hall P.O.
Box 118545 Gainesville,
FL 32611-8545 maydede@phil.ufl.edu |
Güven
Güzeldere Duke
University Department
of Philosophy 201
West Duke Building Box
90743 Durham,
NC 27708 guven@duke.edu |
ABSTRACT. This essay is a sustained attempt to
bring new light to some of the perennial problems in philosophy of mind
surrounding phenomenal consciousness and introspection through developing an
account of sensory and phenomenal concepts. Building on the information-theoretic framework of Dretske
(1981), we present an informational psychosemantics as it applies to what we
call sensory concepts, concepts that apply, roughly, to so-called secondary
qualities of objects. We show that
these concepts have a special informational character and semantic structure
that closely tie them to the brain states realizing conscious qualitative experiences. We then develop an account of introspection
which exploits this special nature of sensory concepts. The result is a new class of concepts,
which, following recent terminology, we call phenomenal concepts: these concepts refer to
phenomenal experience itself and are the vehicles used in introspection. On our account, the connection between
sensory and phenomenal concepts is very tight: it consists in different
semantic uses of the same cognitive structures underlying the sensory concepts,
such as the concept of red.
Contrary to widespread opinion, we show that information theory contains
all the resources to satisfy internalist intuitions about phenomenal consciousness,
while not offending externalist ones.
A consequence of this account is that it explains and predicts the
so-called conceivability arguments against physicalism on the basis of the
special nature of sensory and phenomenal concepts. Thus we not only show why physicalism is not threatened by
such arguments, but also demonstrate its strength in virtue of its ability to
predict and explain away such arguments in a principled way. However, we take the main contribution
of this work to be what it provides in addition to a response to those
conceivability arguments, namely, a substantive account of the interface
between sensory and conceptual systems and the mechanisms of introspection as
based on the special nature of the information flow between them.
1 INTRODUCTION
The
current manifestation of the mind-body problem primarily centers around a deep
disagreement between materialists and anti-materialists about the ontological
nature of phenomenal consciousness.
Facing the charge that they lack the conceptual resources to understand
the phenomenal, materialists are challenged to accept the existence of
non-physical properties, or, at a minimum, admit to being completely in the
dark regarding how to bridge the “explanatory gap” between the physical and the
phenomenal. Joseph Levine, in his
recent book (2001), concludes his lengthy discussion of the explanatory gap
with this challenge:
What emerges from our discussion is that the
explanatory gap is intimately connected to the special nature of phenomenal
concepts. E-type materialists
[exceptionalists] try to save materialism from the conceivability argument by
arguing that phenomenal concepts are special in some way. Well, I grant that, but then we have
the problem of providing an explanation in physicalistic terms of that very specialness,
and we don’t seem to have one. If
we could explain the explanatory gap, then either it would go away or we would
just learn to live with it. But it
seems we can’t do that without a good account of phenomenal concepts, and
that’s something we don’t have. We
lack both an account of phenomenal properties and phenomenal concepts. (p. 86)
In this essay, we provide both. The overarching goal of our project is to present a
sustained and thorough information-theoretic argument that sheds new light on
the problems surrounding phenomenal consciousness, especially the problem of
the explanatory gap.
Building on the information-theoretic framework of Dretske
(1981), we first develop an informational psychosemantics for what we call sensory
concepts,
i.e., concepts that apply, roughly, to so-called secondary qualities of objects. We show that these concepts have a
special informational and semantic character that ties them closely to the
brain states realizing conscious experiences from which they are acquired. We then develop an account of phenomenal
concepts
utilizing this special character of sensory concepts. Phenomenal concepts are those concepts we use in
introspecting our experiences and their qualities. It is through these concepts that we conceive of the
phenomenal character of our experiences.
On our account, sensory and phenomenal concepts turn out to share the
same cognitive structures but their semantics are differently anchored. What makes this possible is the dual
informational content of these structures. In the end, it is the special nature of phenomenal concepts
that enables us to meet the anti-materialist challenge. Further, contrary to widespread
opinion, we show that informational psychosemantics contains the resources to
satisfy internalist intuitions about phenomenal consciousness in a principled
way, while not offending externalist ones.
Our account contributes to what appears to be a growing
convergence of views, sometimes loosely grouped under the label of “perspectivalism,”[1]
which in recent years have been developed in response to conceivability
arguments against physicalism.[2] In its typical versions, perspectivalism
is advanced in three stages.
First, it diagnoses the puzzle involved in attempting to conceive the
phenomenal in terms of the physical as a Frege puzzle — namely, as one
arising from distinct but co-denotational concepts. Second, it points out that the Frege case at hand is special
in a way that marks it off from standard Frege cases, and that this specialness
needs accounting for. Third, it
postulates a group of concepts, typically called “phenomenal concepts,” whose
nature is said to be perspectival, a fact that is supposed to reveal what is so
special about our epistemic access to the phenomenal qualities of our
experiences.
We think that extant perspectivalist accounts are lacking in
precisely those respects that are crucial for the acceptability of physicalist
responses to the conceivability arguments. At the heart of the debate is a set of intuitions about the
conceivability of a range of scenarios (e.g., zombies, inverted spectra). The debate centers around what these
intuitions show. The
anti-physicalists want to draw a metaphysical conclusion (namely, the falsity
of physicalism) from the conceivability of these scenarios. Thus, the question of whether
conceivability, which is an epistemic affair, entails metaphysical possibility
becomes one of the crucial issues.
The perspectivalist materialists with whom we join forces in this paper[3]
maintain that no such metaphysical conclusion follows, but they tend to
restrict their claim only to those cases where the scenarios involve phenomenal
consciousness as it relates to the physical world (after all conceivability
seems to be our only guide to possibility). Thus, at a global scale, many perspectivalists grant that
given a complete physical description of the world and competence with common
concepts that apply to macro phenomena, it is possible in principle to derive a
priori
all true claims about macro phenomena.
For instance, given complete physical knowledge (augmented with standard
indexical information, etc.), it is not conceivable that water should boil at a
temperature other than 0º C at sea level.
They also grant to anti-physicalists that facts about phenomenal
consciousness (and only these facts) cannot be so derived. But they refuse to draw any metaphysical
conclusion from that.
It is the special nature of phenomenal concepts that is
supposed to discharge the heavy explanatory burden the perspectivalists incur
by this refusal. Understandably,
the absence of a principled and independently motivated story about phenomenal
concepts that would justify taking this “exceptionalist” route has made
perspectivalists vulnerable to accusations of special pleading. On standard accounts, phenomenal
concepts turn out to have just those features (simple, primitive, unanalyzable,
demonstrative, etc.) that happen to make them immune to absorption into a
general logical reduction pattern.
But where these features come from and what independent reasons we have
to believe that they work this way are left mostly unexplained. Phenomenal concepts are claimed to be
special, but the critics of physicalism are justified in their demand that
their special character needs to be independently grounded in a general and naturalistic
account of concept formation and use.
That is, whatever it is about these concepts that are supposed to
justify making consciousness an exception to an otherwise perfectly general
pattern needs to fall out naturally from a general and independently motivated
account of conscious experience and the concepts it gives rise to.
In other words, the account of phenomenal concepts must be
part of a more general theory whose explanatory power should go beyond justifying
the exception and saving materialism.
Levine (2001) rightly points out that perspectivalists haven’t so far
produced an independently motivated general and naturalistic account with
sufficient and credible detail.[4] This work constitutes an attempt to develop
such an account — a principled and independently motivated physicalist
story, using the resources of information theory, about the special nature of
phenomenal concepts, and their role in explaining why there is an explanatory
gap of the sort not present in other phenomena.
We derive such an account from a cognitive architectural
framework and general informational psychosemantics of sensory concepts
together with an information-theoretic account of introspection. Fundamentally, we agree with Gareth
Evans on the philosophical utility of construing human beings as “gatherers,
transmitters, and storers of information,” for “these platitudes locate perception,
communication, and memory in a system — the informational system —
which constitutes the substratum of our cognitive lives” (Evans, 1982:
122). As such, our work is in the
spirit of previous attempts to provide naturalized information-theoretic
accounts of thought and reference (Evans 1982, Barwise and Perry 1983, Israel
and Perry 1990, Fodor 1987, 1990).
But our greater debt is to Fred Dretske’s seminal work, Knowledge and
the Flow of Information (1981), which first brought the resources of information
theory into debates in epistemology and philosophy of mind in a ground-breaking
way.[5] As will be apparent in the coming
sections, our account also provides an unexpected synthesis of otherwise quite
diverse views. For instance, it
has consequences that we believe should satisfy internalists about phenomenal
consciousness, while integrating intuitions that motivate both higher-order
perception and higher-order thought accounts of consciousness (even though our
view does not itself fall under these labels).
We ask the reader to bear with us while we lay the
groundwork for our account before we come to the last section (§9) of this
rather lengthy essay, where we ultimately respond to the conceivability
arguments against physicalism. In
the next section (§ 2), in a somewhat reconstructed form and sometimes using
different terminology, we will present the bare bones of an
information-theoretic account of concept formation (from sensory experiences)
based on Dretske (1981).[6] We will be substantially modifying and
developing this account in the remaining sections: in particular, in §§
3–8, we will apply this account to sensory concepts and derive from it an
account of phenomenal concepts and introspection. In §§ 6–7, we will pay close attention to bodily sensations
(especially, pain) and the sensory concepts they give rise to, because we believe
that these sensations and the way we think about them form the microcosm of a
more general mechanism of introspection.
Although we will discuss the conceivability arguments in the last
section (§9), we submit that by that time the reader will be in a position to
see where the real action is.
Indeed, we take the main contribution of this work to be what it provides
in addition to a satisfying response to the conceivability arguments, namely, a
substantive and detailed account of the interface between sensory and
conceptual systems and the mechanisms of introspection based on the special
nature of the information flow between them.
2 THE ARCHITECTURE OF
INFORMATION FLOW IN COGNITION
Information-theoretic
psychosemantics postulates an architectural distinction between
sensory systems and a central cognitive system controlling the intentional
behavior of the organism. The
sensory system has the job of providing information about one’s environment to
the cognitive system, and normally affects behavior only indirectly, via intermediary
cognitive structures. Sensory
systems hook up with the environment via transducers whose job is to transform
the particular forms of energy impinging on the peripheral sensory organs into
forms usable by the internal perceptual systems. The output of transducers and much of the subsequent
processing in the sensory and perceptual systems appear to be automatic and
unconscious (but see below). The
output of the sensory system is a sensory representation of (some aspects of)
the distal layout that is made available to the central cognitive system.
In this framework, the sensory representations are conscious only insofar as the
information they contain is available to the central conceptual system, even if
the information is not fully put to use.
We will also say that the information contained in sensory representations
is available to the organism consciously only insofar as the organism can conceptualize this
information, i.e., only insofar as the information can be used in the acquisition
or deployment of the relevant concepts.[7] Hence, we will use “having an
experience” (which is generally but not necessarily a conscious affair) and “tokening
a sensory representation” interchangeably.[8] We will come back to this point later
on, but for the rest of this paper we will concern ourselves with sensory
representations that are conscious in this way. Hence we will not further discuss those modular (pre- or intra-perceptual)
processes whose state-transitions and outputs are not consciously accessible
— that is, which do not constitute direct inputs to the central cognitive
system.[9]
What are the functional determinants of this architectural
distinction? We have already
touched on one: sensory representations don’t normally affect behavior
directly. It is largely the
central cognitive system which controls voluntary behavior through motor systems. So a necessary condition of a cognitive
structure’s being conceptual as opposed to sensory is its executive connections
to behavior. A representation is
sensory (as opposed to perceptual or conceptual — see § 2.2 below), on
the other hand, only if it makes information about one’s environment (internal/bodily
as well as external) available to the conceptual system for further processing,
which normally also makes the representation (experience) conscious.[10] Besides this, the most important
characteristics underpinning the architectural distinction are to be found in
the following five distinctions: vertical vs. horizontal information
processing, sensation vs. perception, analog vs. digital encoding of
information, extractable vs. non-extractable analog information, and
acquisition vs. deployment of concepts.
We explain each of these in the remainder of this section.
2.1 Vertical vs. Horizontal Information
Processing
First,
sensory experiences are supposed to track changes in the environment. In this they are (non-conceptual) representations
whose primary job is to make available to their hosts temporally indexed
information about the environment.
The crucial point here is that sensory experiences normally carry
information about features of the environment: they are responses to environmental
events. As such their
informational value is typically restricted within a time frame sufficient for the
organism to act back on the environment on the basis of this information. In short, sensory representations are
normally stimulus-driven (a fortiori not directly voluntary). We will call this aspect of information
processing vertical information processing.
By contrast, central cognitive processes, such as thinking,
reasoning, remembering, imagining, and daydreaming are normally horizontal forms of information
processing. By this we mean that
they can,
and frequently do,
occur in the absence of a direct causal (i.e., vertical/informational —
see below) relation with the things being thought about. This is perhaps the most important
hallmark of human intentionality.
In contrast to sensory systems, central cognitive systems harbor
representational processes defined over concepts that are not directly prompted
by what those concepts represent.[11]
Although all concepts can be informationally decoupled from
their referents in horizontal processes, most of them can also be used vertically,
so that their tokenings carry information about the (instantiation of the)
property they apply to. In this extended sense of a vertical
process, experience is the necessary intermediary.[12]
In brief, conceptual representations are the kind of cognitive
structures that are capable of being engaged in horizontal processing, whereas
sensory representations are not.[13]
2.2 Sensation vs. Perception
There is
a useful sense in which perception, unlike sensation, is the vertical informational
process whereby objects of sensation and their sensible qualities are
discriminated and recognized, i.e., categorized or classified under concepts.[14] For most perceptual and observational
concepts, this normally takes the form of recovering the information already
(mostly) in the sensory array by computational processes that result in the
tokening of a concept applied to the object of perception. We see this process mainly as one of
information extraction by digitalization or abstraction from a rich array of information
present in analog form in the experience.
The mechanism underlying the formation of primitive sensory concepts and
their vertical deployment is probably hard-wired in concept-using organisms
like us.
According to this scheme, then, visual object recognition,
for instance, however automatic it may be, is mostly a central process,[15]
since it involves categorizing an object under a “visual concept.” Although the process itself appears to
be unconscious and automatic, many features of the output representation (like
variation in light intensities, lines, edges, colors, distance, orientation,
texture, relative position, etc.), apparently utilized in the extraction process,
are also consciously (hence centrally/globally) available. So perception is a central process in
our sense and should be treated as a species of conception.
2.3 Analog vs. Digital Encoding of
Information
Another
determinant of the architecture, most important for our purposes, is captured
by a distinction between the ways in which information is coded in the representations. Here, we follow Dretske’s original
characterization (cf. Dretske 1981: Chapter 3):
(i)
The
most specific information a signal r carries about a source s is the information r carries about s in digital form.
(ii)
If
r
carries more information about s [or, about t (¹s)] in virtue of carrying this digital
information about s, then this extra information is said to be carried by s in analog form.
(iii)
Analog
information is information nested (nomologically or analytically) in the information
carried in digital form.
Note that
according to this characterization a signal always carries information in both
digital and analog form: it’s just that the most specific information is selected
as digital.
The cognitive value of a sensory representation lies largely
in the information about the distal layout it carries in analog form. Its digital informational content is
the most specific information it carries about this layout, which is very rich
not only in detail but also in amount.
The conceptual system is mostly keyed to the information nested in this
specific and rich information. The
analogy here between pictures and sensory representations will be helpful. If we take a color picture of a cubical
object, the picture will carry very rich, detailed, and determinate information
about the size, texture, and orientation of the object, as well as its position
relative to other objects, the illumination conditions, its determinate shades
of color and their brightness across its surface, and so forth. We can think of this very specific and
detailed information as expressible by a very long conjunction. But nested in this most specific information
there will be less specific information implied by it, such as the information
that the object is (just) cubical, that it has (just) six faces, that it has
eight corners, that it is darkly colored, (just) colored, etc. Normally we are interested in the
analog information carried by the picture. We may be interested merely to know that the object depicted
is cubical — discarding the more specific information about its color,
size, orientation, etc. Or,
depending on the situation, we may be interested only in its size or
orientation.
Similarly with sensory representations. The conceptual system mostly exploits the analog information nested
in the digital information carried by sensory representations. In fact, part of what makes a cognitive
structure a conceptual representation is the way it digitalizes the analog
information contained in the sensory representations. Concepts are those representations (subject to the above architectural
constraints) whose most specific informational content is acquired from
information carried (mostly) in analog form by sensory representations. Concepts (except sensory ones —
see below) are designed to selectively respond to and utilize the analog information
contained in sensory representations.
So, for instance, even though we cannot sensorially represent a triangle
without at the same time representing its determinate size, shape, orientation,
etc., we can conceptually represent an object simply as a triangle
without representing anything more specific or determinate about it.[16] Concepts on this scheme are those
structures that are acquired from sensory representations, mostly on the
basis of the analog information they carry.
In this framework, the semantic content of a concept is
identified with the information it carries in digital form. The informational content of a concept, however,
is not unique in the way the semantic content is supposed to be, since a
vertical tokening of a concept will carry all the information nested
in its digital informational content (i.e., in its semantic content). So, for example, when you identify a
geometrical shape as an isosceles triangle, your identification carries more
information about the object nested in its being such a triangle, e.g., that it
has (just) three sides, that it has (just) three corners, that it is (just) a
geometrical shape, that it has a surface area, etc. These separate pieces of information are all carried in
analog form.
2.4 Extractable vs. Non-Extractable Analog
Information
Both
sensory and conceptual representations carry information in both analog and
digital form. But they encode
analog information in fundamentally different ways. In particular:
·
Whereas
there is always some analog information sensory representations carry in extractable format, the (primitive)
conceptual representations carry all their analog information in non-extractable form.[17]
A
sensory representation is physically realized in such a way that its complex
structure allows the analog information contained in it to be extracted by the
conceptual system operating on it.
Of course, what information can be extracted from the sensory
representation doesn’t depend solely on its complex informational structure; it
also depends on the capabilities and the sophistication of the conceptual
system and what other information is available to the system. But, subject to these constraints, it
is necessary for conceptualization that the analog information in the sensory
representation is carried in a form that is extractable, and not all
information carried in analog form is.
To illustrate, consider the example Dretske uses (1981:
138–39).[18] It is possible to carry all the information encoded
by a picture of a scene with a simple/primitive signal, say a buzzer
system. Suppose the buzzer is
activated when and only when a camera attached to the buzzer detects the occurrence
of a situation exactly like the one depicted in the picture. As Dretske notes, computer recognition
programs that rely on whole-template matching procedures approximate this kind
of transition from one form of coding to another. Both structures carry exactly the same information, both
digital and analog. However, we
will say that the buzzer’s buzzing carries the analog information carried by
the picture in a way that is not extractable, whereas the picture carries it in
an extractable form.
This distinction needs to be developed in more detail in
terms of physical constraints on the structures realizing the representations,
but what is intuitively obvious — and all we need for present purposes
— is that the representational format which allows for information
extraction must consist in a structure complex enough to be the only source for subsequent
digitalizations based on it.[19] The activation of the buzzer, though it
carries all the information carried by the picture, is structured in such a way
that does not allow for digitalization of the information it carries in analog
form. Primitive conceptual
representations are like the buzzer system: although their vertical tokenings
carry analog information nested in their digital content, they are structured
in such a way that they cannot serve as the sole basis for digitalization of
this information. This is part of
the reason why primitive concepts are sometimes characterized as discrete representational
structures or symbols.
2.5 Acquisition vs. Deployment of Concepts
Although
the distinction between the acquisition and deployment of concepts is not a
functional determinant of the informational architecture, it is important to
keep in mind for clarificatory purposes.
Both acquisition and deployment can be vertical and horizontal in some intuitively extended
sense. So, for instance, we can
acquire concepts by reading, or by being talked to, by looking at pictures, by
engaging in inference to the best explanation, etc.[20] This would be horizontal acquisition of
concepts. Also note that for the
moment we are using the term “acquisition” in a way that is neutral between triggering and learning.
Now that we have the functional determinants of the
architecture of information flow in cognition and the relevant distinctions,[21]
we will focus on the nature of the concepts to which this architecture gives
rise.
3 CONCEPTS AND THEIR
SENSORY BASES
Among the
concepts directly and immediately acquired from sensory experience are what we
will call sensory concepts.
These form a special class of concepts that will be important for what
follows. Intuitively and roughly
put (to be qualified in a moment), sensory concepts are those concepts whose
digital informational content is also part of the digital informational content
of the sensory representations from which they are acquired, so that the abstraction/digitalization
distance
between the concepts and these experiences is minimal.[22]
The digital informational content of sensory representations
is rich along several dimensions.
We can think of these dimensions as presenting determinables such that
the resolution of our sensory experiences marks the limit of their most
determinate values about which we can gather sensory information. To the extent that we can separate
these dimensions, we can speak of that part of the total digital information
content of an experience that belongs to one of these dimensions fixed by the
modality of the experience. So,
for instance, under conditions that are optimal for color vision, seeing a ripe
tomato will involve a visual experience whose total digital content contains
the most specific information about the color of the tomato: it will represent
the tomato as having a determinate shade of red, say, red16. This is part of the total digital
content of the visual experience containing information about the color of the
object seen. As mentioned above,
we can conceive of this total digital content as being expressed by a very long
conjunction detailing all the most specific information it carries. The particular shade of color that a
region in the visual field has, then, would be one of the conjuncts.[23] Sensory concepts are those concepts
that are closest (in terms of abstraction distance) along these different
dimensions to the digital informational content of experiences from which they
are acquired.
If the property of being red16 is a disjunctive
property whose disjuncts are particular spectral reflectances, then the
information the sensory representation of the tomato carries about red16
is about this disjunctive property.
Every disjunct would be a particular ratio fixed by the percentage of
light that the surface of an object reflects at each of the three
characteristic wavelengths determined by the response sensitivity of three
retinal cone types.[24] But whatever feature of sensory representation
is responsible for carrying this information, it carries it without revealing
its complex and disjunctive character.
For instance, this feature, by carrying information about a surface’s
being red16, also carries the analog information that it has a
spectral reflectance, or that it (just) reflects light at different wavelengths. These are nested in the information
that the surface is red16.
But these pieces of analog information cannot be recovered or extracted
from the signal, i.e., from whatever feature of the sensory representation
carries the color information in question.
There is, however, still some abstraction/digitalization
— some loss of information — in this process. This can be explained in terms of a distinction
between concepts used in synchronic discriminatory tasks and concepts used in
diachronic recognitional or identification tasks. In fact, we typically reserve the notion of a concept for those cognitive
structures involved in the latter sort of task. Consider the tomato again. If the conditions are appropriate, it will be possible to
discriminate slight variations in the shade of red across the surface of the
tomato. But when the same shades
of color are shown to us diachronically we may not be able to discriminate
among them: most of the time the best we can do is identify and co-classify
them as, say, dark red. Both kinds
of task involve discrimination and categorization of different color stimuli,
and so, in this sense, require
conceptual capacities. In what
follows, however, when we talk about sensory concepts, we will have in mind the
most specific concepts one can have as revealed by diachronic recognition
tasks, which involve memory. It is
clear that the abstraction distance between sensory experiences and the sensory
concepts conceived in this way is still minimal, although there is still some
information lost. Notice that in
the case of color concepts this distance can be explained entirely in terms of
set-theoretic notion of inclusion.
When these concepts are vertically deployed, the information they carry
is disjunctive: they say something like “it is either red1 or red2
or red3 or … redn”, where n is finite and redi
is the most determinate shade of red one’s visual experiences can carry information
about and thus be synchronically discriminated.
It is important to note that the disjuncts here are still colors — determinate
shades of red. This is important
because the abstraction process here is not based on information about the
constituents of colors (whatever objective properties color experiences/concepts
detect), which are not themselves colors.
So, for example, if color vision detects sets of individual surface
spectral reflectances, color sensations don’t represent them by representing their
constituent properties, say, individual reflectances or whatever further
properties constitute these reflectances.
Hence, color sensations don’t represent colors as having constituent
structure, or as we will say sometimes for convenience, as simple/atomic properties.[25]
Contrast this to the visual representation of shapes. Our visual system happens to be such
that we can’t visually represent a geometrical figure (in such a way that we
can then recognize it as what it is, say, as a square) without simultaneously
representing the lines, angles, curves, edges, and corners that, in some
intuitive sense, constitute the figure. It is important to note that these constituents are not more
determinate instances of the same figure type, so that even the concept of a
most determinate geometrical figure of that type will not be minimally close to
the sensory base it is directly acquired from — even though these sensory
bases are the sole authoritative source of acquisition for such concepts. We will call such concepts perceptual
concepts. The information necessary and
sufficient for the correct application of these concepts, whose abstraction
distance is nevertheless not minimal (but shorter than what we will call below observational concepts), is normally
contained in the sensory base from which they are directly acquired. Typical perceptual concepts in the case
of vision include concepts of spatiotemporal relations, geometrical figures,
and shapes.
For the sake of completeness, we can distinguish sensory and
perceptual concepts from observational concepts like the concept of an
apple, a robin, a tree, a lake, and a truck. These concepts are also typically acquired from an appropriate
sensory base, but they need not be, and often are not. However, the information contained in
experiences required in the correct application of these concepts is more
impoverished, in the sense that it always underdetermines correct
categorization. In other words,
although the information about the denotations of these concepts can be perceptually
available, its delivery requires that certain channel conditions external to the sensory systems
be in place. The abstraction
distance between these concepts and the sensory bases from which they may be
acquired is considerably greater than in the case of sensory and perceptual
concepts. What seems to mark the
difference is that (most of) the sensory information used in the acquisition
and deployment of observational concepts is typically only contingently related
to the objects in their extensions.
It is no accident that thought experiments involving
spectrum inversion are carried out in terms of sensory bases of sensory concepts,
where the property detected and denoted is represented as simple or atomic.[26] Although we cannot conceive of
inversion with respect to the properties denoted by perceptual concepts (e.g.,
of shapes) and their sensory bases, there is nothing preventing a differently
organized cognitive system from performing this feat. We can imagine and even construct devices that “sensorially”
detect geometrical shapes (quite abstract from our cognitive point of view) by
outputting simple and primitive sensory representations. For instance, we can construct a
detector that responds with a green light when it detects a square (any square) and with a red
light when it detects a circle (any circle).
Suppose that all the information it uses in making its responses is lost
at the final output stage. When
this device, a 2D geometrical shape detector, lights up green, its relevant
state carries the information that something it is informationally connected to
is square. If it lights up red,
its state carries the information that something is circular. But even if the “sensory” outputs of
the device carry these pieces of information, they are structured in such a way
that there is no way to recover any information about the structural
relationships holding among the internal constituents of these shapes. Of course, these “sensory” outputs also
carry information about the constituent properties (necessarily so), but only
in analog form that is not extractable.
Nor is it possible to extract any topological information that obtains
between these different shapes — if the device carries information about
the shapes in a spatial array. For
all the device “knows,” whatever is being represented by these colored lights,
it is simple and atomic. There are
no computational/formal constraints stemming from the representations
themselves that would make the thought experiment of an “inverted shape” unintelligible
here. For all the device “knows,”
circles could look exactly the same to it as squares do now, and vice versa.
If this device is also equipped with a central conceptual
system that can acquire concepts from such “sensory” representations, the concept
of a circle the device directly acquires from its “experiences” will be a sensory (as opposed to perceptual) concept in our
sense. Our concept of a circle is
not sensory because the sensory representations from which it is acquired don’t
carry the information that something is a circle as part of its total digital
informational content so that when our conceptual system digitalizes this piece
of information there is always more specific information that is lost but
nevertheless available to the central cognitive system for digitalization.[27]
Furthermore it is this lost information that seems to be used in the
acquisition and vertical deployment of the target concept. What prevents the abstraction distance
from being minimal here is the existence of more specific but
used-and-then-discarded information that is nevertheless available to the
conceptual system for digitalization (which, subject to some further
conditions, makes this used-but-then-discarded information contained in the experience
consciously available).
In contrast to our perceptual system, the architecture of
this device is such that the abstraction distance between the “sensory” and
“conceptual” representations of circles and squares is minimal. Not surprisingly, we are not such machines. But it is important to keep in mind
that there is no logical necessity in our having the perceptual and cognitive
architecture that we do, including the set of particular abstraction distances
it gives rise to — although there are most likely evolutionary and
ecological reasons for this architecture.[28]
Another way to see what makes sensory concepts so special is
to understand the nature of the abstraction distance between them and their
sensory bases. As we have said,
this distance is minimal (subject to the qualification we have just
introduced), which is what marks these concepts off from the rest. Following Fodor (1990) and Margolis
(1998), we will call the mechanisms that mediate the informational link
between the vertical tokenings of a concept and the instantiations of the
property it applies to sustaining mechanisms.[29] The intra-cranial portion of the sustaining
mechanisms for sensory concepts is not cognitive: since there is (almost) no
loss of information in the acquisition of color concepts, there is nothing
further to be made available to the central system for digitalization. Acquisition of sensory concepts is
therefore brute and primitive: to acquire these concepts it is enough to occupy
the relevant sensory states for an organism equipped with an appropriate
conceptual system — i.e., by an information pick-up system operating on
the sensory representations. This
is why the notion of learning is not appropriate for the acquisition of these
concepts. Rather, the preferred
term for this, for both empiricists and nativists, is “triggering.” So one sense in which the abstraction
distance is minimal is that the process underlying the acquisition and vertical
deployment of sensory concepts does not involve any loss of information that is
nevertheless available to the conceptual system for further digitalization.
Contrast this to the intra-cranial sustaining mechanisms for
other concepts, which are (partially but essentially) cognitive. The acquisition and deployment of
perceptual concepts may be innate and automatic in some sense, but these still
involve a digitalization process with considerable loss of information, information
that is still available for digitalization. When we visually recognize shapes of objects or geometrical
figures, most of the information about their spatially distributed and
organized constituents (illumination gradients, edges, corners, curves, color,
etc.) is still consciously available.
It isn’t that we consciously use this information in the acquisition and
deployment of such concepts — this is something our perceptual (as
opposed to sensory) systems automatically do for us. But what is interesting is that even though this process may
be automatic and unconscious, most of the information used in the process
(which is then discarded) is available to us, to the central
cognitive system, and thus is conscious in just that sense. Because of the importance and
centrality of perceptual concepts, their acquisition may still be innately
determined — i.e., such concepts may be triggered rather than
learned. We leave this issue open.
The notion of learning seems most appropriately applied to
the acquisition of observational (and for that matter, theoretical) concepts. The sustaining mechanisms for those
concepts are heavily cognitive, involving the use and loss of a great amount of
information, which is also normally consciously available.[30] Generally, the more cognitive the sustaining
mechanisms of a concept are, the greater the abstraction distance between it
and the sensory bases from which it is acquired.
Before we move on to examine what makes sensory concepts
special, we would like to make a few observations about what is implied by the
architecture of the information flow from the sensory to the conceptual. If we are right, then there is a deep
point to be made about autonomous representational systems:
(i)
Such
systems are nomologically bound to be hooked up to their environments in a way
that at some level of abstraction they will always harbor sensory
representations that represent complex physical properties in their environment
as simple or atomic, or rather, do not represent them as having internal complexity.
(ii)
Furthermore:
necessarily, if an autonomous intentional organism has concepts at all (or a
conceptual system, as opposed to just sensory representations), however
primitive or sophisticated, then it has some sensory concepts in our
sense.
One of the most basic truths about autonomous intentional
systems is that they have to interact with their environment informationally. So they have to have information entry
mechanisms. These mechanisms
cannot deliver every piece of information in analog form, i.e., in a form that
is always nested by some further more specific information. There will have to be a cut-off point
about the most specific information the mechanism can provide about the environment. If this piece of digital information
carries the analog information nested in it in an extractable format, then
there will have to be structural features of the output representation carrying
the (total) digital information that nest this information. Then the same question arises about the
digital content of these features and its format. This process cannot go indefinitely. At some point there will have to be
representational features with digital informational content that nests the
analog information carried by them in a non-extractable format, at which point
the property digitally represented won’t be represented as having internal
constituents — if the property has internal constituents (this can be a
massively disjunctive property like colors). As will become clear as we proceed, it is these necessities
that partly create the mystery around phenomenal consciousness.
4 WHAT MAKES SENSORY
CONCEPTS SPECIAL
It is not
accidental that the distinction we drew between sensory and perceptual concepts
is approximately coextensive with the distinction traditionally drawn between
concepts of secondary and primary qualities, respectively.[31] Secondary qualities are those which are
represented in our experiences in a primitive way: sensory representations
carry information about them in a way that makes the information carried about
their constituents analog but non-extractable. (It is the job of empirical
scientific investigation to reveal the complex nature of secondary qualities,
and extract the information about their constituents.) Hence, sensory experiences carry the
most specific information about these properties without revealing their
internal structure. This is why
the abstraction distance between the concepts of secondary qualities and their
sensory bases is minimal; equivalently, this is why the acquisition of these
concepts is non-cognitive and brute.
Sensory concepts apply, in the first instance, to the
objects of perception, to whatever it is that our sensory experiences
represent.[32] This is so despite the fact that they
are directly and immediately acquired from sensory representations. The flow of information required for
their acquisition (and vertical deployment) necessitates the presence of sensory
intermediaries that carry information about the properties denoted by these
concepts. Indeed, this is one of
the main differences between sensory and observational concepts.[33] There is an asymmetry in their
acquisition: while sensory concepts are necessarily acquired from the
experiences sensorially representing the properties they denote, observational
concepts are different.
Observational concepts are typically acquired from experiences
representing their denotations, but this is not necessary. We can acquire them “horizontally,”
i.e., by sensory means (speech perception, seeing pictures, reading
books/newspapers, inference, etc.) that are only very indirectly related to,
and hence don’t carry information about, their denotations.
There is a deep reason for this asymmetry which we haven’t
touched on so far but will be very important for what follows: the information
about the secondary qualities contained in experiences cannot be completely
digitalized
by the conceptual system, whereas the conceptual system can completely
digitalize the information contained in experiences about the properties
denoted by observational concepts.[34] “Complete digitalization” is a
technical term introduced by Dretske that expresses a necessary condition for a
piece of information to count as the semantic content of a concept. Recall that the semantic content of a
concept is the most specific information its vertical tokenings carry about the
objects it applies to, which is equated with its digital informational
content. But Dretske eventually
refines this definition by requiring that the semantic content be that piece of
information which is completely digitalized. Here is the definition (1981: 185):
Structure S has the fact that t is F as its semantic content
[i.e., S
is the concept of an F] =definition
(a) S carries the information
that t
is F
and
(b) S carries no other piece
of information, r
is G,
which is such that the information that t is F is nested (nomically or analytically) in r’s being G.
Condition
(b) ensures that if S carries the information that t is F, it does so not by
carrying information about any intermediary which nests the information that t is F. When the two conditions are satisfied S carries the information
that t
is F
in completely digital form, or equivalently, S is said to completely
digitalize the information that t is F, which then becomes S’s semantic
content. More intuitively, the
intention is to rule out those cases where concepts carry the most specific
distal information about an object by carrying information about their proximal
causes, in our case their sensory bases.[35] So, for instance, the concept ROBIN,
when acquired from experiences that carry information about robins, should not
carry information about the structure of sensory representations that give rise
to ROBIN.[36] Since we are working in a naturalistic
framework, if concepts carried information about sensory representations from
which they are acquired, this information would be information about the instantiation
of certain neurophysiological properties (or disjunctive sets of such
properties) realizing these sensations.
Hence our concepts would be selectively responding to such properties in
the first place. And this would
imply either that our concepts represent neurophysiological conditions, or that
our sensory concepts have dual semantic content, and therefore are
systematically ambiguous.
Interestingly, Dretske does not make a point about the
empirical impossibility of complete digitalization; nor does he talk about the
fact that complete digitalization is routinely violated in the case of sensory
concepts.[37] If sensory representations of secondary
qualities are realized by a more or less homogeneous set of neurophysiological
properties, or by a finite disjunction of such properties, then vertical
tokenings of sensory concepts carry information about their distal causes
(instantiations of secondary qualities) by carrying information about the
instantiations of these proximal physical properties. Whether or not experiences of such qualities are physically
realized in a homogeneous way is ultimately an empirical question, but we think
that there is enormous empirical as well as a priori evidence that this is
the case — certainly intrapersonally, and most probably interpersonally.[38] What is important for our purposes is
the claim that the neurophysiological
realization bases of sensory representations of such qualities are not
indefinitely and arbitrarily varied, but consist of a finite disjunctive set of
physical properties, and are more or less homogeneous in just this sense. We think that this claim is true, but
we stand ready to be corrected by future empirical evidence.
There are also overwhelmingly strong engineering reasons for
this claim: whenever you make an architectural distinction between a sensory
buffer and a conceptual system that extracts information about the distal
layout from this buffer (and whose behavior is causally sensitive to what this
buffer contains), there will be a need to correlate the information carried by
concepts and the elements of the buffer in such a way that matches up with the
distal layout. If the only way the
conceptual system carries information about the distal properties is through a
physically realized sensorium, then it had better be the case that the same
elements of this sensorium carried the same information, at least in the case
of secondary qualities where the abstraction distance is minimal. Otherwise, the informational efforts of
the conceptual system will be fooled.
From an engineering perspective, it is unclear how such an architectural
design can be constructed without making the realization bases of those sensory
representations more or less physically homogeneous (i.e., not arbitrarily
varied), at least within a single system.[39]
Notice that in the case of observational concepts there is
no real problem about complete digitalization. There are indefinitely many ways robins, trucks, etc. can
affect our sensory receptors, and thus many ways in which they can be
represented in experience. In such
cases, the standard information-theoretic remedy is to say that these concepts
track their distal causes without tracking proximal sensory representations,
since the alternative is to say that they track a massively (probably
open-ended) disjunctive proximal property. We believe that the former is indeed more plausible than the
latter. But if so, we can now see
better why sensory representations carrying information about properties
denoted by observational concepts are not necessary for acquiring such concepts. These concepts, though observational,
are modality-neutral (amodal), and to that extent not perspectival. But that is not to say that their
cognitive sustaining mechanisms don’t involve sensory/perceptual channels and
concepts; they do. It is to say,
however, that the sustaining mechanisms involved provide information only
(mostly) contingently related to the denotation of these concepts.
It is the failure of complete digitalization that makes
sensory concepts special by giving them a perspectival and quasi-indexical character. Their acquisition, semantics, and
vertical deployment are essentially host-unique in two senses:
(i)
It
matters essentially for whose cognitive system these cognitive structures function
as concepts.
(ii)
They
track features of the environment (instantiations of secondary qualities
however objectively understood) essentially by tracking something about
their host,
namely, the sensory experiences from which they are directly acquired.
In other
words, these are concepts which a properly functioning conceptual system cannot normally acquire unless
suitably hooked up to a properly functioning sensory/perceptual information
delivery system of the same host that has actually delivered the necessary
information, i.e., carried information about the properties denoted by these
sensory concepts.[40] We also want to emphasize that their
acquisition is direct and immediate, by which we mean this: their sustaining/acquisition
mechanisms are not cognitive, but primitive and brute; that is, they don’t
involve the exploitation of consciously available information that is then
discarded in the digitalization process.
This is roughly to say that the abstraction distance involved in their
acquisition is minimal. In the
context of our discussion above, this implies that no information about the
internal constituents of the properties denoted by sensory concepts is
available in an extractable format: they don’t represent their denotations as
having a complex internal structure.
All these points about sensory concepts will be crucially important
later on, when we criticize conceivability arguments against physicalism.[41]
5 FIXING THE SEMANTIC CONTENT
OF SENSORY CONCEPTS
What
justifies the claim that, despite the failure of complete digitalization, the
semantic content of a sensory concept, say RED, is the secondary quality, redness, possessed by the objects of the sensory
experiences from which we directly acquire it?[42] Irrespective of what semantic content
our theories assign to these concepts, there should be no doubt about what
their semantic contents are: they are the qualities that our experiences
represent the external objects as having.
Our experiences place these qualities in the world of objects external
to our bodies. So do our sensory
concepts. Given this, the question
before us is how to reconcile a Dretskean informational semantics with the failure
of complete digitalization. For
even if we rightly want to be able to say that RED represents redness despite the failure of
complete digitalization, what justifies rejecting the option, which seems to be
a consequence of the theory, that the semantic content of RED is the experience of redness, i.e., E-red, realized
by a certain set of neurophysiological properties?
Here is another way of putting the problem. Informational semantics starts with the
information carried by a structure on its way to working out how to determine
its semantic
content (SC). We have seen that Dretske wants to assign
the completely digitalized informational content of a concept (C) as its semantic
content: in other words,
·
the
semantic content is the most specific information carried by C about a source o such that there is no
separate structure e such that C carries the most specific information about o by carrying the most
specific information about e.