Theories of Consciousness

The Cognitive Neurosciences IV, M. Gazzaniga (ed.), MIT Press, 2009
COMPARING THE MAJOR THEORIES OF
CONSCIOUSNESS
Ned Block
NYU

Original at

http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/Theories_of_Consciousness.pdf

Abstract
This article compares the three frameworks for theories of consciousness
that are taken most seriously by neuroscientists, the view that consciousness is a
biological state of the brain, the global workspace perspective and an account in
terms of higher order states. The comparison features the “explanatory gap”
(Levine, 1983; Nagel, 1974) the fact that we have no idea why the neural basis of
an experience is the neural basis of that experience rather than another
experience or no experience at all. It is argued that the biological framework
handles the explanatory gap better than do the global workspace or higher order
views. The article does not discuss quantum theories or “panpsychist” accounts
according to which consciousness is a feature of the smallest particles of
inorganic matter (Chalmers, 1996; Rosenberg, 2004). Nor does it discuss the
“representationist” proposals (Byrne, 2001a; Tye, 2000) that are popular among
philosophers but not neuroscientists.
Three Theories of Consciousness

Higher Order The higher order approach says that an experience is
phenomenally conscious only in virtue of another state that is about the
experience (Armstrong, 1978; Byrne, 1997, 2001b; Carruthers, 2000; Lycan,
1996a; Rosenthal, 2005a). This perspective comes in many varieties, depending
on, among other things, whether the monitoring state is a thought or a
perception. The version to be discussed here says that the higher order state is
a thought (“higher order thought” is abbreviated as “HOT”), and that a conscious
experience of red consists in a representation of red in the visual system
accompanied by a thought in the same subject to the effect that the subject is
having the experience of red.
Global Workspace The global workspace account of consciousness was first
suggested by Bernard Baars (1988), and has been developed in a more neural
direction by Stanislas Dehaene, Jean-Pierre Changeux and their colleagues
(Dehaene, Changeux, Nacchache, Sackur, & Sergent, 2006). The account
presupposes a neural network approach in which there is competition among
neural coalitions involving both frontal and sensory areas (Koch, 2004), the
winning coalitions being conscious. Sensory stimulation causes activations in
sensory areas in the back of the head that compete with each other to form
dominant coalitions (indicated by dark elements in the outer group of rings in
Figure 1). Some of these dominant coalitions trigger central reverberations via
long range connections to frontal cortex, setting up activations that help to
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maintain both the central and peripheral activations. The idea that some brain
areas control activations and reactivations in other areas is now ubiquitous in
neuroscience (Damasio & Meyer, 2008), and a related idea is widely accepted:
that one instance of reciprocal control is one in which workspace networks in
frontal areas control activations in sensory and spatial areas (Curtis &
D’Esposito, 2003). It is useful in thinking about the account to distinguish
between suppliers and consumers of representations. Perceptual systems
supply representations that are consumed by mechanisms of reporting,
reasoning, evaluating, deciding and remembering, which themselves produce
representations that are further consumed by the same set of mechanisms.
Once perceptual information is “globally broadcast” in frontal cortex this way, it is
available to all cognitive mechanisms without further processing. Phenomenal
consciousness is global broadcasting.
Although the global workspace account is motivated and described in part
in neural terms, the substantive claims of the model abstract away from neuronal
details. Nothing in the model requires the electrochemical nature of actual neural
signals. The architectural aspects of the model can just as easily be realized in
silicon based computers as in protoplasm. In this respect, the global workspace
theory of consciousness is a form of what philosophers call “functionalism”
(Block, 1980), according to which consciousness is characterized by an abstract
structure that does not include the messy details of neuroscience.
Another functionalist theory of consciousness is the integrated information
theory (Tononi & Edelman, 1998) according to which the level of consciousness
of a system at a time is a matter of how many possible states it has at that time
and how tightly integrated its states are. This theory has a number of useful
features, for example retrodicting that there would be a loss of consciousness in
a seizure in which the number of possible states drops precipitously (Tononi &
Koch, 2008). Unfortunately, such predictions would equally follow from an
integrated information theory of intelligence (in the sense of the capacity for
thought, as in the Turing Test of intelligence)–which also drops in a seizure.
Consciousness and intelligence are on the face of it very different things. We all
understand science fiction stories in which intelligent machines lack some or all
forms of consciousness. And on the face of it, mice or even lower animals might
have phenomenal consciousness without much intelligence. The separation of
consciousness and cognition has been crucial to the success of the scientific
study of consciousness. In a series of papers that established the modern study
of consciousness (Crick & Koch, 1990, 1998), Crick and Koch noted in particular
that the basic processes of visual consciousness could be found in non-primate
mammals and were likely to be independent of language and cognition. Although
its failure to distinguish consciousness and intelligence is crippling for the
integrated information theory as a stand-alone theory of consciousness, I will
mention it at the end of the article in a different role: as an adjunct to a biological
theory.
The biological theory The third of the major theories is the biological theory, the
theory that consciousness is some sort of biological state of the brain. It derives
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from Democritus (Kirk, Raven, & Schofield, 1983) and Hobbes (1989), but was
put in modern form in the 1950s by Place (1956), Smart (1959) and Feigl (1958).
(See also Block, 1978; Crane, 2000; Lamme, 2003.) I will explain it using as an
example the identification of the visual experience of (a kind of) motion in terms
of a brain state that includes activations of a certain sort (involving feedback
loops) in area MT+ of the visual cortex. Although useful as an example, we can
expect that any theory of visual experience will be superseded.
Visual area MT+ reacts to motion in the world, different cells reacting to
different directions. Damage to MT+ can cause loss of the capacity to
experience this kind of motion, MT+ is activated by the motion after-effect,
transcranial magnetic stimulation of MT+ disrupts these afterimages and also can
cause motion “phosphenes” (Britten, Shadlen, Newsome, & Movshon, 1992;
Cowey & Walsh, 2000; Heeger, Boynton, Demb, Seideman, & Newsome, 1999;
Huk, Ress, & Heeger, 2001; Kammer, 1999; Kourtzi & Kanwisher, 2000; G.
Rees, Kreiman, & Koch, 2002; Théoret, Kobayashi, Ganis, Di Capua, & Pascual-
Leone, 2002; Zihl, von Cramon, & Mai, 1983). However, it is important to
distinguish between two kinds of MT+ activations, what I will call nonrepresentational
activations and representational activations. Some activations in
the visual system are very weak, do not “prime” other judgments (that is, do not
facilitate judgments about related stimuli), and do not yield above chance
performance on forced choice identification or detection (that is they do not allow
subjects to perform above chance on a choice of what the stimulus was or even
whether there was a stimulus or not). On a very liberal use of the term
‘representation’ in which any neural activation that correlates with an external
property is a representation of it (Gallistel, 1998), one might nonetheless call
such activations of MT+ representations, but it will be useful to be less liberal
here, describing the weak activations just mentioned as non-representational.
(The term ‘representation’ is very vague and can be precisified in different
equally good ways.) However, if activations of MT+ are strong enough to be
harnessed in subjects’ choices (at a minimum in priming), then we have genuine
representations. (See Siegel, 2008 for a discussion of the representational
contents of perceptual states.)
Further, there is reason to think that representations in MT+ that also
generate feedback loops to lower areas are at least potentially conscious
representational contents (Pascual-Leone & Walsh, 2001; Silvanto, Cowey,
Lavie, & Walsh, 2005). (For a dissident anti-feedback loop perspective see
Macknik and Martinez-Conde (2007).) Of course an activated MT+ even with
feedback to lower visual areas is not all by itself sufficient for phenomenal
consciousness. No one thinks that a section of visual cortex in a bottle would be
conscious (Kanwisher, 2001).
What makes such a representational content phenomenally conscious?
One suggestion is that active connections between cortical activations and the
top of the brainstem constitutes what Alkire (Alkire, Haier, & Fallon, 2000) calls a
“thalamic switch”. There are two important sources of evidence for this view.
One is that the common feature of many if not all anesthetics appears to be that
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they disable these connections (Alkire & Miller, 2005). Another is that the
transition from the vegetative state to the minimally conscious state (Laureys,
2005) involves these connections. However, there is some evidence that the
“thalamic switch” is an on-switch rather than an off-switch (Alkire & Miller, 2005)
and that cortico-thalamic connections are disabled as a result of the large overall
decrease in cortical metabolism (Alkire, 2008; Tononi & Koch, 2008; Velly et al.,
2007)—which itself may be caused in part by the deactivation of other subcortical
structures (Schneider & Kochs, 2007). Although this area of study is in flux, the
important philosophical point is the 3 way distinction between (1) a nonrepresentational
activation of MT+ (2) an activation of MT+ that is a genuine
visual representational of motion, and (3) an activation of MT+ that is a key part
of a phenomenally conscious representation of motion.
The same distinctions can be seen in terms of the global workspace
theory as the distinction between (1) a minimal sensory activation (the gray
peripheral activations in Figure 1), (2) a peripheral dominant coalition (the black
peripheral activations in Figure 1) and (3) a global activation involving both
peripheral and central activation (the circled activations in Figure 1 that connect
to the central workspace). The higher order account can accommodate these
results but is focused on the distinction between a visual representation and a
conscious visual representation (2 vs 3), a visual representation that is
accompanied by a higher order thought to the effect that the subject has it.
Here are some items of comparison among the 3 theories. According to
the biological account, global broadcasting and higher order thought are what
consciousness does rather than what consciousness is. That is, one function of
consciousness on the biological view is to promote global broadcasting, and
global broadcasting in some but not all cases can lead to higher order thought.
Further, according to the biological view, both the global workspace and higher
order thought views leave out too many details of the actual working of the brain
to be adequate theories of consciousness. Information in the brain is coded
electrically, then transformed to a chemical code, then back to an electrical code,
and it would be foolish to assume that this transformation from one form to
another is irrelevant to the physical basis of consciousness.
From the point of view of the biological and global workspace view, the
higher order thought view sees consciousness as more intellectual than it is, but
from the point of view of higher order thought accounts, the biological and global
workspace accounts underestimate the role of cognition in consciousness. The
global workspace and higher order thought accounts are sometimes viewed as
superior to the biological account in that the biological account allows for the
possibility that a subject could have a phenomenally conscious state that the
subject does not know about (Block, 2007a, 2007b). And this is connected to the
charge that the biological account—as compared with the other accounts–
neglects the connection between phenomenal consciousness and the self
(Church, 1995; Harman, 1995; Kitcher, 1995).
The higher order and global workspace accounts link consciousness to
the ability to report it more tightly than does the biological view. On the higher
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order thought view, reporting is just expressing the higher order thought that
makes the state conscious, so the underlying basis of the ability to report comes
with consciousness itself. On the global workspace account, what makes a
representational content conscious is that it is in the workspace, and that just is
what underlies reporting. On the biological account, by comparison, the
biological machinery of consciousness has no necessary relation to the biological
machinery underlying reporting, and hence there is a real empirical difference
among the views that each side seems to think favors their own view (Block,
2007b; Naccache & Dehaene, 2007; Prinz, 2007; Sergent & Rees, 2007).
To evaluate and further compare the theories, it will be useful to appeal to
a prominent feature of consciousness, the explanatory gap.
The Explanatory Gap
Phenomenal consciousness is “what it is like” to have an experience
(Nagel, 1974). Any discussion of the physical basis of phenomenal
consciousness (henceforth just consciousness) has to acknowledge the
“explanatory gap” (Levine, 1983; Nagel, 1974): nothing that we now know,
indeed nothing that we have been able to hypothesize or even fantasize, gives
us an understanding of why the neural basis of the experience of green that I
now have when I look at my screen saver is the neural basis of that experience
as opposed to another experience or no experience at all. Nagel puts the point in
terms of the distinction between subjectivity and objectivity: the experience of
green is a subjective state but brain states are objective, and we do not
understand how a subjective state could be an objective state or even how a
subjective state could be based in an objective state. The problem of closing the
explanatory gap (the “Hard Problem” as Chalmers (1996) calls it) has four
important aspects: (1) we do not see a hint of a solution, (2) we have no good
argument that there is no solution that another kind of being could grasp or that
we may be able to grasp at a later date (But see McGinn, 1991.) So (3) the
explanatory gap is not intrinsic to consciousness, and (4) most importantly for
current purposes, recognizing the first three points requires no special theory of
consciousness. All scientifically oriented accounts should agree that
consciousness is in some sense based in the brain; once this is accepted, the
problem arises of why the brain basis of this experience is the basis of this one
rather than another one or none and it becomes obvious that nothing now known
gives a hint of an explanation.
The explanatory gap was first brought to the attention of scientists through
the work of Nagel and Crick and Koch (Crick, 1994; Crick & Koch, 1998). I would
argue that the candid recognition of what we do and more importantly do not
understand played an important role in fueling the incredible wave of research
that still engulfs us.
How do the three theories account for the explanatory gap?
The HOT view says that consciousness of, say red, is a matter of three
ingredients: a higher order thought, a representation with the content red, and an
aboutness relation between the first and the second. According to the HOT
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perspective, each of these ingredients can exist individually without any
consciousness. We have unconscious, e.g. subliminal representations of red, we
have unconscious thoughts and those unconscious thoughts are, unconsciously,
about things. According to the HOT theory, if a subject has an unconscious
representation of red, and then forms an unconscious thought about the
representation of red, the representation of red automatically is conscious. Of
course in some trivial sense of ‘conscious’ we might decide to call that
representation of red conscious, meaning only that there is a higher order
thought about it; but if the HOT theory is about consciousness in the full blooded
sense in which for a state to be conscious is for there to be something it is like to
be in that state, there is a fundamental mystery for the HOT view.
It may seem that this is just the explanatory gap in a new form, one
appropriate to the HOT theory, but that is a mistake. Consider the prime order
thought (POT) view—that says that thoughts about thoughts about thoughts…are
always conscious so long as the number of embeddings is prime. There is a
puzzle of the POT view’s own making of why a prime number of embeddings
creates consciousness, but that puzzle is not the real explanatory gap.
The real explanatory gap is the problem of why the neural basis of a
conscious state with a specific conscious quality is the neural basis of that
conscious quality rather than another or nothing at all. The real explanatory gap
does not assume any specific theory except the common basis of all scientific
approaches in the 21st Century, that conscious qualities have a brain basis.
The problem for the HOT perspective is that it is part of the idea of it that
putting together ingredients that are not in themselves conscious (thought,
aboutness and representation) automatically exhibits consciousness. The most
neuroscience can do is explain thought, explain aboutness and explain
representation. But there is no reason to expect—and it is not part of any HOT
perspective–that neuroscience will find some magic glow that occurs when those
things combine.
The fact that the HOT theory cannot recognize the real explanatory gap
makes it attractive to people who don’t agree that there is an explanatory gap in
the first place—the HOT theory is a kind of “no consciousness” theory of
consciousness. But for those who accept an explanatory gap (at least for our
current state of neuroscientific knowledge), the fact that the HOT theory doesn’t
recognize one is a reason to reject the HOT theory. The HOT theory is geared to
the cognitive and representational aspect of consciousness, but if those aspects
are not the whole story, the HOT theory will never be adequate to
consciousness.
This very short argument against the HOT approach also applies to the
global workspace theory, albeit in a slightly different form. According to the global
workspace account, the answer to the question of why the neural basis of my
experience of red is the neural basis of a conscious experience is simply that it is
globally broadcast. But why is a globally broadcast representation conscious?
This is indeed a puzzle for the global workspace theory but it is not the
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explanatory gap because it presupposes the global workspace theory itself,
whereas the explanatory gap (see above) does not.
The most neuroscience can do for us according to the global workspace
account is explain how a representation can be broadcast in the global
workspace, but the task will still remain of explaining why global broadcasting,
however realized, is conscious. In principle, global broadcasting could be
realized in an electronic system rather than a biological system, and of course
the same issue will arise. So that issue cannot be special to the biological
realization of mind.
The biological account, by contrast, fits the explanatory gap—indeed I
phrased the explanatory gap above in terms of the biological account, asking
how we can possibly understand how consciousness could be a biological
property. So the biological account is the only one of the three major theories to
fully acknowledge the explanatory gap. From the point of view of the HOT and
global workspace theories, their task concerning the explanatory gap is not to
show how they can accommodate it, but rather to explain away our impression
that there is one. One such attempt will be considered in the next section.
There is a fine line between acknowledging the explanatory gap and
surrendering to dualism, as also discussed in the next section.
The Explanatory Gap and Dualism
Dualism is the view that there is some aspect of the mind that is not
physical (Chalmers, 1996). It comes in many varieties, but the issues to be
discussed do not depend on any specific variety.
Let us start with a historical analogy (Nagel, 1974). A pre-Socratic
philosopher would have no way of understanding how heat could be a kind of
motion or of how light could be a kind of vibration. Why? Because the pre-
Socratic philosopher did not have the appropriate concepts of motion—namely
the concept of kinetic energy and its role–or of vibration—namely the concepts
involved in the wave theory of light–that would allow an understanding of how
such different concepts could pick out the same phenomenon.
What is a concept? A concept is a mental representation useable in
thought. We often have more than one concept of the same thing. The concept
light and the concept electromagnetic radiation of 400-700 nm pick out the same
phenomenon. What the pre-Socratic philosopher lacks is a concept of light and
an appropriate concept of vibration (one that requires a whole theory). What is
missing for the pre-Socratic is not just the absence of a theoretical definition but
a lack of understanding of what things are grouped together from a scientific
point of view. We now realize that ripples in a pond, sound and light are all
phenomena of the same kind: waves. And we now realize that burning, rusting
and metabolizing are all cases of oxidation (Churchland, 2002) but the pre-
Socratics, given their framework in which the basic categories were fire, earth, air
and water would have had no way to grasp these facts. One upshot is that if
super-scientists of the future were to tell us what consciousness is, we probably
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would not have the conceptual machinery to understand, just as the pre-Socratic
would not have the conceptual machinery to understand that heat is a kind of
motion or that light is a kind of vibration.
Armed with this idea, we can see how to steer between the explanatory
gap and dualism. What we lack is an objective neuroscientific concept that
would allow us to see how it could pick out the same phenomenon as our
subjective concept of the experience of green. And we can expect that we don’t
even have the right subjective concept of the experience of green since we are
not sure what subjective phenomena truly should be grouped together. The
resolution of the apparent conflict between the explanatory gap and physicalism
is that subjectivity and objectivity can be seen as properties of concepts rather
than properties of the states that the concepts are concepts of. This idea, that
we can see arguments that apparently indicate ontological dualism, that is a
dualism of objects or substances or properties, as really an argument for
conceptual dualism, stems from Nagel 1974 and Loar (Loar, 1990/1997) and is
sometimes called “New Wave” physicalism. (See Horgan & Tienson, 2001).
Another way of seeing the point is to consider Jackson’s (1982) famous
thought experiment concerning Mary, a neuroscientist of the distant future who
knows everything there is to know about the scientific basis of color experience,
but grows up in a black and white environment. When she sees red for the first
time, she learns what it is like to see red, despite already knowing all the
scientific facts about seeing red. Does this show that the fact of what it is like to
see red is not a scientific fact? No, because we can think of what Mary learns in
terms of her acquiring a subjective concept of a state that she already had an
objective concept of. Imagine someone who already knows that Lake Michigan
is filled with H2O, but learns something new: that Lake Michigan is filled with
water. What this person learns is not a new fact but a new piece of knowledge,
involving a new concept, of a fact the person already knew. Similarly, Mary
acquires new knowledge, but that new knowledge does not go beyond the
scientific facts that she already knew about, and so does not support any kind of
dualism. (This line of thought is debated in (Block, 2006; White, 2006).
Importantly, this line of reasoning does not do away with the explanatory
gap but rather reconceives it as a failure to understand how a subjective and an
objective concept can pick out the same thing.
These points about different concepts of the same thing has sometimes
been used to try to dissolve the explanatory gap (Papineau, 2002). The idea is
that the false appearance of an explanatory gap arises from the gap between a
subjective concept of a phenomenally conscious state and an objective concept
of the same state. But note: I can think the thought that the color I am now
experiencing as I look at an orange (invoking a subjective concept of orange) is
identical to the color between red and yellow (invoking an objective concept of
orange). But this use of the two kinds of concepts engenders no explanatory
gap.
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Thus far, the score is: biological theory 1, HOT and global workspace 0.
But the competition has not yet encountered the heartland of the HOT theory.
Consciousness-of
It is very often (but not always–(Dretske, 1993)) assumed that a conscious
state is a state that one is conscious of being in (Lycan, 1996a). I would agree,
though with the caution that the point may be a verbal one. The HOT theory has
an attractive of consciousness-of, because consciousness-of can be cashed out
as: being the object of a HOT. However, there are two other accounts of why a
conscious state is one that one is conscious of being in, and these accounts are
preferable to the HOT account—according to the viewpoint of the biological
theory and the global workspace theory. The deflationary account (Sosa, 2003)
says that all there is to being conscious of one’s experience is the triviality that in
having an experience, one experiences it, just as one smiles one’s smile and
dances one’s dance. Consciousness-of in this sense is to be firmly distinguished
from attending to one’s experience (Burge, 2006). One can have a conscious
experience of red and that experience can have whatever awareness comes with
conscious experience, even in the absence of top-down attention to it (Koch &
Tsuchiya, 2007). Another rival to the higher order account of why a conscious
state is one that one is conscious of is the same order account in which a
conscious pain is reflexive in that it is about itself. That is, it has a content that
turns back on itself, and that is what makes a pain a state one is conscious of.
This view had its beginnings in Aristotle (Caston, 2002) and was later pursued by
Brentano (1874/1973). (See Burge, 2006; Kriegel & Williford, 2006.) Either one
of the deflationary or same order accounts can be adopted by advocates of the
biological view and the global workspace view, so I see no real advantage for the
HOT view here.
Further Problems for the HOT Theory
I argued above that the HOT theory cannot recognize an explanatory gap,
but my argument was oversimple because it neglected a crucial distinction
between two types of HOT theories. The kind of HOT theory that cannot
recognize an explanatory gap is the ambitious HOT theory of phenomenal
consciousness that analyzes phenomenal consciousness in terms of higher order
thought. But there is also a modest and therefore innocuous form of the HOT
theory that just says that, in addition to phenomenal consciousness, there is
another kind of consciousness, higher order consciousness. Phenomenal
consciousness is one thing and higher order consciousness is another. The
modest form can recognize an explanatory gap for phenomenal consciousness.
The modest account is suggested by Lycan’s remark “ [I] cannot myself hear a
natural sense of the phrase ‘conscious state’ other than as meaning ‘state one is
conscious of being in” (Lycan, 1996b). As Lycan recognizes, what one can and
cannot “hear” leaves the theoretical options open. The modest account is
tantamount to a verbal claim—that there is a sense of the term ‘conscious’
(distinct from ‘phenomenal consciousness’) that has a higher order meaning—
and does not dictate that there is no explanatory gap. The very short argument
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against the HOT theory (that it doesn’t recognize an explanatory gap and so is
false) is an argument only against the ambitious form of the HOT theory. In the
rest of this section, I will explain some other problems with the ambitious HOT
theory that also do not apply to the modest version.
The first thing to realize about the HOT theory in both the ambitious and
modest forms is it needs considerable qualification. Suppose I consciously infer
that I am angry from my angry behavior, or in a slightly different kind of case that
need not involve conscious inference: I am aware of my anger in noticing my
angry fantasies. In these cases we wouldn’t say the anger is thereby conscious.
Further, Freudians sometimes suppose that a subject can unconsciously
recognize his own desire to, for example, kill his father and marry his mother and
the need to cloak that desire in a form that won’t cause damage to the self. But
we would not say that in virtue of such an unconscious HOT (one that cannot
readily become conscious) about it, the desire is therefore conscious! These
examples concerning what we would say suggest that a HOT about a state is not
something we regard as sufficient for the state to be conscious. Defenders of the
HOT theory introduce complications in the HOT theory to try to avoid these
counterexamples. Rosenthal (2005a) says that S is a conscious state if and only
if S is accompanied by a thought to the effect that the subject is in S that is
arrived at without inference or observation of which the subject is conscious. The
italicized phrase avoids the problems posed by conscious observation of angry
fantasies and conscious inference by stipulating that HOTs arrived at by
conscious observation and inference are not sufficient for consciousness.
(Another stipulation that I won’t describe is supposed to handle the Freudian
issue.) Suppose as a result of biofeedback training I come to have noninferential
non-observational knowledge of states of my liver (Block, 1995).
Since we wouldn’t count the state of the liver as conscious in virtue of the HOT
about it, Rosenthal (2000b, p. 240) further stipulates that only mental states can
be conscious. What if I have a HOT about my future or past mental state?
Rosenthal (2000b, p. 241) further stipulates that if one has a thought about a
state, that makes it conscious only when one thinks of it as present to oneself.
As Bertrand Russell noted in an often quoted passage (1919, p. 71), “The
method of “postulating” what we want has many advantages; they are the same
as the advantages of theft over honest toil.“ Honest toil is not required if the HOT
view is understood as a modest account, since stipulation is not a problem in a
stipulated sense of a term, but ad hoc stipulation is a problem if we take the HOT
view as an ambitious account, especially as an empirical theory of
consciousness.
A second class of issues concerns the “mismatch problem”, the possibility
of a mismatch in content between a sensory representation and the
accompanying HOT. What phenomenally conscious quality does an experience
have if a HOT to the effect that one has a dull throbbing pain in the toe is
accompanied not by any representation of toe-damage but instead a visual
representation of red—or by no sensory representation at all? If the sensory
representation determines the conscious quality all by itself, the contents of
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HOTs are irrelevant here and if here, why not elsewhere? And if the HOT
determines the conscious quality without the sensory representation, then the
contents of sensory representations are irrelevant—so what is the difference
between thinking you have a delightful experience and actually having one
(Balog, 2000; Byrne, 1997; Levine, 2001; Neander, 1998; Rey, 2000)? Of course
new sophistication in one’s HOTs, as when one learns to recognize different
wines can cause a corresponding differentiation in the sensory states that the
HOTs are about, but HOTs are not always causally self-fulfilling (If only!!!) and in
any case, causal self-fulfillment does not answer the constitutive question of what
the difference is between thinking you have an experience of a certain sort and
actually having one. Rosenthal (2000a, 2000b; 2005b, p. 217-219) claims that a
HOT is sufficient for a conscious state even without any sensory representation
that the HOT is about. But suppose I have a sharp pain that causes a HOT to
the effect that I have a sharp pain, through the normal processes via which pains
often cause metacognitions about them. And suppose that by chance I also
have a qualitatively different sharp pain (one pain is a bit sharper than the other)
that produces no HOT at all. The content of the HOT—that I have a sharp pain–
doesn’t distinguish between the two pains even though by any ordinary standard
it is about one of them but not the other. If the HOT theory follows common
sense, saying that one pain is conscious but the other is not, it is hard to see how
that (partly causal) way of cashing out aboutness could be compatible with the
claim that a HOT to the effect that I am in pain could be a conscious pain on its
own without any sensory representation.
A third class of issues concerns children. If you have seen and heard a
circumcision, you may find it difficult to doubt that it hurts. Relevant evidence:
newborns who are circumcised without anesthesia or analgesia are more
stressed by later vaccination even 6 months later (Taddio, Goldbach, Ipp,
Stevens, & Koren, 1995). My point is not that you should be totally convinced of
phenomenal consciousness in early infancy, but rather that you should be
convinced that there is a better case for phenomenal consciousness in infancy
than there is for those instances of phenomenal consciousness being
accompanied by higher order thought.
One point against higher order thought in infancy is that frontal cortex, the
likely neural home of thought about thought (Stone, Baron-Cohen, & Knight,
1998) is immature in infancy. Gazzaniga, Ivry, & Mangun (2002, p. 642-643)
discuss two sources of evidence that areas of the brain that specialize in sensory
and motor function develop significantly earlier than areas responsible for
thinking. One source of evidence derives from autopsy results on human brains
from age 28 weeks after conception to 59 years of age. The result, diagrammed
in Figure 2, is that auditory synaptic density peaks at about 3 months (and
probably likewise for synaptic density in other sensory areas), whereas the
association areas of the frontal cortex peak at about 15 months. Similar results
apply to PET imaging which measures glucose metabolism in different parts of
the brain.
12
As infants become more mature, our confidence in their phenomenal
consciousness increases, as does our confidence in their capacity for higher
order thought. However, it continues to be doubtful that phenomenally conscious
states are always accompanied by higher order thoughts. Children even up to
age 3-4 have difficulty thinking about their own states of mind. For example,
Alison Gopnik and her colleagues (Gopnik & Graf, 1988) used a tube that was
open at both ends and contained a window that could be open or closed. The
child would be asked to either look in the window or reach into the side and
identify a common object, e.g. a spoon. Then with the apparatus taken away, the
child was asked how he or she knew the spoon was in the tube. The children
were nearly random in their answers, probably because, as Gopnik has pointed
out in a series of papers (see Gopnik, 2007), they have difficulty attending to and
thinking about their own representational states. Marjorie Taylor and her
colleagues have compared “source amnesia” for representational states of mind
with skills (Esbensen, Taylor, & Stoess, 1997). For example, some children were
taught to count in Japanese, whereas other children were taught the Japanese
word for ‘three’. Children were much less likely to be able to name the source of
their representational state than the source of their counting skill. (E.g. “You just
taught me” in answer to the skill question vs. “I’ve always known” in answer to
the representational state question.) The source amnesia results apply most
directly to conscious intentional states rather than conscious perceptual states,
but to the extent that perceptual states are representational, they may apply to
them as well. Older autistic children who clearly have phenomenally conscious
states also have problems attending to and thinking about representational states
of mind (Baron-Cohen, 1995; Charman & Baron-Cohen, 1995). Will a defender
of the ambitious HOT theory tell us that these autistic children lack phenomenal
states? Or that contrary to the evidence they do have HOT states?
I emphasize that it is difficult for young children and autists to think about
representational states of mind—but not impossible. Indeed, children as young
as 13 months can exhibit some ability to track others’ beliefs (Onishi &
Baillargeon, 2005; Surian, Caldi, & Sperber, 2007). In the case of false belief, as
in many other examples of cognition, a cognitive achievement is preceded by a
highly modular and contextualized analog of it, one that partly explains the
development of the cognitive achievement. My point is not that meta-cognition in
all its forms is impossible in young children and autists but that at all ages, our
justification for attributing conscious states exceeds our justification for attributing
meta-cognitive states.
Although the empirical case against the higher order thought point of view
is far from overwhelming, it is strong enough to make the question salient of what
the advantages of the ambitious higher order thought theory of consciousness
actually are (as contrasted with the advantages of the modest version, which
none of these points apply to).
But how do we know whether a version of the HOT theory is ambitious or
modest? One way to tell is to ask whether on that theory, a phenomenally
conscious state—considered independently of any HOT about it–is something
13
that is bad or good in itself. For example, Carruthers famously claimed
(Carruthers, 1989, 1992) that because pains in dogs, cats, sheep, cattle, pigs
and chickens are not available to be thought about, they are not felt and hence
not anything to be concerned about, that is, they are states with no moral
significance. (Carruthers later took a different view (1999) on the ground that
frustration of animal desires is of moral significance even though the pains
themselves are not.)
I turn now to related issues about the self that may seem to go against the
biological view.
The Self
The biological view may seem at a disadvantage with respect to the self.
Since Hume (Hume, 1740/2003) described the self as “that connected
succession of perceptions”, many (Dennett, 1984; Parfit, 1984) have thought
about persons in terms of integrated relations among mental states. The global
workspace view seems well equipped to locate consciousness as self-related
given that broadcasting in the global workspace is itself a kind of integration.
And the HOT view at least requires the integration of one state being about
another. By contrast, it looks as if on many views of the biological basis of a
conscious state (Block, 1995), it could exist without integration, and this point has
resulted in accusations of scanting the self (Church, 1995; Harman, 1995;
Kitcher, 1995). One response would be to favor a biological neural basis of
consciousness that itself involves integration (Tononi & Edelman, 1998; Tononi &
Koch, 2008). But it is worth pointing out that phenomenal consciousness has
less to do with the self than critics often suppose.
What is the relation between phenomenal consciousness and the self?
We could raise the issue by thinking about pain asymbolia, a syndrome in which
patients have pain experiences without the usual negative affect (Aydede, 2005):
they don’t seem to mind the pain. In this syndrome, patients sometimes describe
the pains as painful for someone else, and perhaps they are right given pain’s
unusual lack of connection to the subject’s emotions, planning and valuation.
Here is a question about such a dissociation syndrome: If such a subject thinks
about the painfulness of such a pain (as opposed to its merely sensory aspect),
is the painfulness thereby phenomenally conscious? It would seem not,
suggesting that the kind of integration supplied by HOTs is not actually sufficient
for consciousness.
Here is another conundrum involving the relation between phenomenal
consciousness and the self. In many experiments, activation in the fusiform face
area at the bottom of the temporal lobe has been shown to correlate with the
experience of a face. Now, injury to the parietal lobe often causes a syndrome
called visuo-spatial extinction. If the patient sees a single object, the patient can
identify it, but if there are objects on both the right and the left, the patient claims
not to see one—most commonly the one on the left. However two fMRI
studies(G. Rees et al., 2000; G. Rees, Wojciulik. et al., 2002) have shown that in
patient GK, when GK claims not to see a face on the left, his fusiform face area
14
lights up almost as much as when he reports seeing the face. One possibility is
that the original identification of the fusiform face area as the neural basis of face
experience was mistaken. But another possibility is that the subject genuinely
has face experience that he doesn’t know about and cannot know about. Wait—
is that really a possibility? Does it even make sense to suppose that a subject
could have an experience that he doesn’t and can’t know about? What would
make it his experience?
The question about GK can be answered by thinking about the subject’s
visual field? What is the visual field? We could define the visual field as the
subject’s visual representation of space. Consider how the visual field is
measured. If you look straight ahead and hold a rod out to the side and slowly
move it forward, you will be able to see it at roughly 100o from the forward angle.
If you do the same coming down from the top, you will see it at roughly 60o, and if
you do it from the bottom, you will see it at roughly 75o. A more accurate
mesurement can be obtained with points of light or gratings. It turns out that the
normal visual field (in the sense of the cross-section of the space represented) is
an oval, elongated to the right and left, and slightly larger on the bottom. The
Humphrey Field Analyzer HFA-II-I can measure your visual field in as little as 2
minutes. The United Kingdom has a minimum visual field requirement for driving
(60o to the side, 20o above and below); US states vary widely in their
requirements (Peli & Peli, 2002). I mention these details to avoid skepticism
about whether the visual field is real.
The visual field can help us think about GK. If GK does genuinely
experience the face on the left that he cannot report, then it is in his visual field
on the left side, and as such has relations to other items in his visual field, some
of which he will be able to report. The fact that it is his visual field shows that it is
his experience. I caution the reader that this discussion concerns the issue of
whether it makes sense to describe GK as having an experience that he can’t
know about and does not constitute any evidence for his actually having an
experience that he can’t know about (but see Block, 2007a).
A second point about the relation between phenomenal consciousness
and the self is that self-related mental activities seem inhibited during intense
conscious perception. Malach and his colleagues (Goldberg, Harel, & Malach,
2006) showed subjects pictures and audio clips with two different types of
instructions. In one version, subjects were asked to indicate their emotional
reactions as positive, negative or neutral. In another version (in which the stimuli
were presented much faster), subjects were asked to categorize the stimuli, for
example, as animals or not. Not surprisingly, subjects rated their self-awareness
as high in the introspective task and low in the categorization task. And this
testimony was supported by fMRI results that showed that the introspective task
activated an “intrinsic system” that is linked to judgments about oneself whereas
the categorization task inhibited the intrinsic system, activating instead an
extrinsic system that is also activated when subjects viewed clips from Clint
Eastwood’s “The Good, the Bad and the Ugly”. Of course this result does not
show that intense perceptual experiences are not part of a connected series of
15
mental states constituting a self, but it does suggest that theories that bring any
sense of self into phenomenal experience are wrongheaded. Malach’s result
disconfirms the claim that a conscious visual experience consists in a perceptual
state causing a thought to the effect that I myself have a visual experience
(Rosenthal, 2005a).
Machine Consciousness
The global workspace account lends itself particularly well to the idea of
machine consciousness. There is nothing intrinsically biological about a global
workspace. And the HOT view also is friendly to machine consciousness. If a
machine can think, and if it can have representational contents, and if it can think
about those contents, it can have conscious states, according to the HOT view.
Of course we do not know how to make a machine that can think, but whatever
difficulties are involved in making a machine think, they are not difficulties about
consciousness per se. (However, see Searle (1992) for a contrary view.) By
comparison, the biological theory says that only machines that have the right
biology can have consciousness, and in that sense, the biological account is less
friendly to machine consciousness. Information is coded in neurons by electrical
activations that travel from one part of a neuron to another, but in the most
common type of transfer of information between neurons, that electrical coding is
transformed into a chemical coding (via neurotransmitters) which transfer the
information to another neuron where the coding of information is again electrical.
On the biological view, it may well be that this transfer of coding of information
from electrical to chemical and back to electrical is necessary to consciousness.
Certainly it would be foolish to discount this possibility without evidence.
As should be apparent, the competitors to the biological account are
profoundly non-biological, having more of their inspiration in the computer model
of the mind of the 1960s and 1970s than in the age of the neuroscience of
consciousness of the 21st Century. (For an example, see McDermott, 2001.) As
Dennett (2001, p. 234) confesses, “The recent history of neuroscience can be
seen as a series of triumphs for the lovers of detail. Yes, the specific geometry of
the connectivity matters; yes, the location of specific neuromodulators and their
effects matter; yes, the architecture matters; yes, the fine temporal rhythms of the
spiking patterns matter, and so on. Many of the fond hopes of opportunistic
minimalists [a version of computationalism: NB] have been dashed: they had
hoped they could leave out various things, and they have learned that no, if you
leave out x, or y, or z, you can’t explain how the mind works.” Although Dennett
resists the obvious conclusion, it is hard to avoid the impression that the biology
of the brain is what matters to consciousness—at least the kind we have–and
that observation favors the biological account.1
16
Figure 1 Schematic diagram of the global workspace. Sensory activations in
the back of the brain are symbolized by dots and lines in the outside group of
rings. Dominant sensory neural coalitions (dark lines and dots) compete with
one another to trigger reverberatory activity in the global workspace (located in
frontal areas) in the center of the diagram. The reverberatory activity in turn
maintains the peripheral excitation until a new dominant coalition wins out.
Figure 2
17
Relative synaptic density of auditory and frontal cortex. Conceptual age is age
from conception. The peak at the left of roughly 3 months (postnatal) reflects a
high number of auditory synapses relative to frontal synapses. From (Gazzaniga
et al., 2002)
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1 Acknowledgements: I am grateful to Susan Carey, Peter Carruthers, Christof Koch,
David Rosenthal and Stephen White for comments on an earlier version.

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