Can a Photodiode Be Conscious?

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.

1. 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.

1. 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.