Can a Photodiode Be Conscious?
MARCH 7, 2013
Christof Koch and Giulio Tononi, reply by John R. Searle
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IN RESPONSE TO:
Can Information Theory Explain Consciousness? from the January 10, 2013 issue
To the Editors:
The heart of John Searle’s criticism in his review of Consciousness: Confessions of a Romantic
Reductionist [NYR, January 10] is that while information depends on an external observer,
consciousness is ontologically subjective and observer-independent. That is to say, experience
exists as an absolute fact, not relative to an observer: as recognized by Descartes, je pense donc
je suis is an undeniable certainty. Instead, the information of Claude Shannon’s theory of
communication is always observer-relative: signals are communicated over a channel more or
less efficiently, but their meaning is in the eye of the beholder, not in the signals themselves.
So, thinks Searle, a theory with the word “information” in it, like the integrated information
theory (IIT) discussed in Confessions, cannot possibly begin to explain consciousness.
Except for the minute detail that the starting point of IIT is exactly the same as Searle’s!
Consciousness exists and is observer-independent, says IIT, and it is both integrated (each
experience is unified) and informative (each experience is what it is by differing, in its
particular way, from trillions of other experiences). IIT introduces a novel, non-Shannonian
notion of information—integrated information—which can be measured as “differences that
make a difference” to a system from its intrinsic perspective, not relative to an observer. Such a
novel notion of information is necessary for quantifying and characterizing consciousness as it
is generated by brains and perhaps, one day, by machines.
Another of Searle’s criticisms has to do with panpsychism. If IIT accepts that even some simple
mechanisms can have a bit of consciousness, then isn’t the entire universe suffused with soul?
Searle justly states: “Consciousness cannot spread over the universe like a thin veneer of jam;
there has to be a point where my consciousness ends and yours begins.” Indeed, if
consciousness is everywhere, why should it not animate the iPhone, the Internet, or the United
States of America?
Except that, once again, one of the central notions of IIT is exactly this: that only “local
maxima” of integrated information exist (over elements, spatial and temporal scales): my
consciousness, your consciousness, but nothing in between; each individual consciousness in
the US, but no superordinate US consciousness. Like Searle, we object to certain kinds of
panpsychism, with the difference that IIT offers a constructive, predictive, and mathematically
precise alternative.
Finally, we agree with Searle that one looks in vain for mouthwatering admissions of guilt in
Confessions. That is true from the point of view of a priest eager for sins to be revealed. Yet
among scientists, there exists a powerful edict against bringing subjective, idiosyncratic
memories, beliefs, and desires into professional accounts of one’s research. Confessions breaks
with this taboo by mixing the impersonal and objective with the intensely personal and
subjective. To a scientist, this is almost a sin. But philosophers too can get close to sin, in this
case a sin of omission: not to ponder enough, before judgment is passed, what the book and
ideas one reviews are actually saying.
Christof Koch
Chief Scientific Officer
Allen Institute for Brain Science
Seattle, Washington
Giulio Tononi
Professor of Psychiatry
University of Wisconsin
Madison, Wisconsin
John R. Searle replies:
One of my criticisms of Koch’s book Consciousness is that we cannot use information theory to
explain consciousness because the information in question is only information relative to a
consciousness. Either the information is carried by a conscious experience of some agent (my
thought that Obama is president, for example) or in a nonconscious system the information is
observer-relative—a conscious agent attributes information to some nonconscious system (as I
attribute information to my computer, for example).
Koch and Tononi, in their reply, claim that they have agreed with this all along, indeed it is
their “starting point,” and that I have misrepresented their theory. I do not think I have and will
now quote passages that substantiate my criticisms. (In this reply I will assume they are in
complete agreement with each other.)
1. The Conscious Photodiode. They say explicitly that the photodiode is conscious. The crucial
sentence is this:
Strictly speaking, then, the IIT [Integrated Information Theory] implies that even a binary
photodiode is not completely unconscious, but rather enjoys exactly 1 bit of consciousness.
Moreover, the photodiode’s consciousness has a certain quality to it….*
This is a stunning claim: there is something that it consciously feels like to be a photodiode! On
the face of it, it looks like a reductio ad absurdum of any theory that implies it. Why is the
photodiode conscious? It is conscious because it contains information. But here comes my
objection, which they claim to accept: the information in the photodiode is only relative to a
conscious observer who knows what it does. The photodiode by itself knows nothing. If the
“starting point” of their theory is a distinction between absolute and observer-relative
information, then photodiodes are on the observer-relative side and so are not conscious.
2. The Observer Relativity of Integrated Information. They think they get out of the observer
relativity of information by considering only integrated information, and integrated information,
they think, is somehow absolute information and not just relative to a consciousness. But the
same problem that arose for the photodiode arises for their examples of integrated information.
Koch gives several: personal computers, embedded processors, and smart phones are three.
Here is an extreme claim by him:
Even simple matter has a modicum of Φ [integrated information]. Protons and neutrons consist
of a triad of quarks that are never observed in isolation. They constitute an infinitesimal
integrated system. (p. 132)
So on their view every proton and neutron is conscious. But the integrated information in all of
these is just as observer-relative as was the information in the photodiode. There is no intrinsic
absolute information in protons and neutrons, nor in my personal computer, nor in my smart
phone. The information is all in the eye of the beholder.
3. Panpsychism. They claim not to be endorsing any version of panpsychism. But Koch is
explicit in his endorsement and I will quote the passage over again:
By postulating that consciousness is a fundamental feature of the universe, rather than emerging
out of simpler elements, integrated information theory is an elaborate version of
panpsychism.(p. 132, italics in the original)
And he goes on:
The entire cosmos is suffused with sentience. We are surrounded and immersed in
consciousness; it is in the air we breathe, the soil we tread on, the bacteria that colonize our
intestines, and the brain that enables us to think. (p. 132)
Any system at all that has both differentiated and integrated states of information is claimed to
be conscious (Koch, p. 131). But my objections remain unanswered. Except for systems that are
already conscious, the information in both simple systems like the photodiode and integrated
systems like the smart phone is observer-relative. And the theory has a version of panpsychism
as a consequence.
But the deepest objection is that the theory is unmotivated. Suppose they could give a definition
of integrated and differentiated information that was not observer-relative, that would enable us
to tell, from the brute physics of a system, whether it had such information and what
information exactly it had. Why should such systems thereby have qualitative, unified
subjectivity? In addition to bearing information as so defined, why should there be something it
feels like to be a photodiode, a photon, a neutron, a smart phone, embedded processor, personal
computer, “the air we breathe, the soil we tread on,” or any of their other wonderful examples?
As it stands the theory does not seem to be a serious scientific proposal.
1. * Giulio Tononi, “Consciousness as Integrated Information: A Provisional Manifesto,” The
Biological Bulletin, Vol. 215, No. 3 (December 2008), pp. 216–242, quotation from p.
236. ↩
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