This essay was written in March 2002, when I was in tenth grade. I happened to find the original text on my computer and post it here for a look; the problem remains the problem.
September 5, 2006
1．Introduction
Where does consciousness reside? You may answer without hesitation: consciousness is a function of the human brain. But have you ever thought: which part of the human brain does consciousness reside in? How does the human brain produce consciousness? Will strong AI have consciousness? Can one “consciousness” reside in multiple brains; and how many consciousnesses might one brain possess?
I cannot answer these questions very well; these are questions that even the most first-rate scientists and philosophers have pushed away unanswered. I am only putting some questions before you to ponder, and I believe that after reading this article you will also have your own unique insights.
Limited by space, here I will only briefly discuss some issues of the “stream of consciousness,”
Like the “flow of time,” the “stream of consciousness” is an illustrative way of speaking. The “stream of consciousness” in the mental world is just like the “flow of time” in the material world: the endpoints of the flow of time are birth and extinction in the material world; the endpoints of the stream of consciousness are life and death in the living world. You can perceive the “directionality” of the flow of time because time is projected onto your directional stream of consciousness. In the many-worlds theory, the flow of time may “branch,” that is, give rise to multiple “parallel universes”[①], while the “stream of consciousness” seems not to “split.” This is what I am going to discuss.
Here “consciousness” mainly includes “self-consciousness,” and “self-consciousness” should be the hallmark of intelligent beings. What exactly counts as “self-consciousness” is highly controversial: some say higher animals (such as chimpanzees) also have self-consciousness; the more extreme even say ants and fleas have it too! At the other extreme, some say prehistoric humans did not have self-consciousness! But one thing you should not object to—you do have “self-consciousness.” What we are discussing is this kind of “self-consciousness” that you possess.
2．A thought experiment that causes the stream of consciousness to branch
In many science-fiction works you can see this kind of thing: a person walks into a supermachine, the supermachine scans him, converts the arrangement of all the particles in his body into data, transmits it at the speed of light to another star system for reassembly, while the original body is dismantled. This is what is called “instantaneous transfer.” In fact, this cannot be realized, because the data required to describe a person is simply too vast. But this does not violate the laws of physics, so one cannot rule out an infinitely advanced civilization realizing this kind of “instantaneous transfer.”
And if such technology really existed, one could simply make several copies of a person or choose not to destroy the original body. If a person were copied into two versions, how would that person’s “stream of consciousness” proceed? If no mark were made on the original body, then no one would know which one was the true “him.” And because of the continuity of the stream of consciousness, both “he’s” would think the other was the copy, so whether subjectively or objectively, the two “he’s” are completely equivalent! Since consciousness cannot control two people at the same time, it can be said that in “copying” the “stream of consciousness” has branched!
3．Where consciousness resides and an empirical example of the branching of the stream of consciousness
Consciousness is produced by the human brain; most people would not object to that. But which part of the human brain produces consciousness? On this question there are many different opinions, and so far there has still not been a satisfactory answer—some say it is the “reticular formation”; some say the thalamus and midbrain; some say the “hippocampus”; some say the cerebral cortex. These views all have their reasons. More philosophers and psychologists believe that consciousness resides in the “language center,” the Wernicke and Broca areas[②]. But this view is also unreasonable: are those congenitally deaf-mute people supposed to have no consciousness? And among mathematical prodigies, the great majority claim that when they think they “do not use verbal language,” and clinical observation has found that when people display conscious phenomena, the “language center” is not always in an active state. Personally, I think consciousness is more like something produced by the combined action of all parts of the brain; the organic integration of the various parts is a process from quantitative change to qualitative change, and among them the cerebral cortex should play a key role.
We know that the left and right hemispheres are symmetrical yet divided in labor—the left hemisphere is responsible for the comprehension and formation of language and writing; the right hemisphere is responsible for geometric thinking and art appreciation, and so on. The left hemisphere is responsible for the tactile sensation and movement of the right side of the body, hearing in the right ear, and vision in the right half of the visual field, while the right hemisphere is the opposite[③]. Such a division of labor makes the “corpus callosum,” which connects the left and right hemispheres for the exchange of information, especially important.
For some unfortunate epilepsy patients, removing the corpus callosum may be the best surgical treatment. Many psychologists abroad have conducted experiments on these patients whose corpus callosum has been severed: the patient’s left and right visual fields are simultaneously exposed to completely separate stimuli: a picture of a pencil flashes on the right, and a picture of a cup flashes on the left. The patient will say, “That is a pencil,” while the left hand will choose a plate to match the cup (rather than choosing an eraser or something like that to match the pencil). This is because the “language center” is in the left hemisphere; although the right hemisphere cannot speak, it behaves as if it were an independent person.
Of course, in the experiment above, the left and right hemispheres are not completely separated; their emotions are shared. But obviously no one would think that “emotion” is where consciousness resides. Some people think that even if the right hemisphere has consciousness, it is very primitive, because it cannot even understand the most basic sentences. But the question will not be brushed aside so easily. A man named Donald Wilson and his collaborators carried out a striking experiment in 1977: a patient with the code name “P.S.”, after split-brain surgery, although only the left hemisphere could speak, both hemispheres could understand language, and later the right hemisphere even learned to speak! Moreover, the two hemispheres actually displayed different preferences—for example, the left hemisphere said it hoped to become a cartographer while the right hemisphere hoped to become a race-car driver! I do not know the details of the experiment, but its credibility is quite high.
We see P.S. displaying two different consciousnesses, and this phenomenon is frightening. I cannot help wondering: how did his “stream of consciousness” “flow”? Clearly, during the surgery, his “stream of consciousness” had not been “broken off”; from before the surgery to after the surgery, his “stream of consciousness” was continuous, just as it is when you sleep and then wake up. For either hemisphere, it had merely lost part of its memory and temporarily lost some of the functions of the other hemisphere—and it might even be able to learn[④]—while its consciousness remained continuous; it knew clearly that it was the person before the surgery. Here, the left and right hemispheres are completely equal, which is to say that the “stream of consciousness” has branched!
You may think: “If I underwent such a terrifying operation, when I woke up would I be the left hemisphere or the right hemisphere?” This question is extremely hard to explain: obviously, your consciousness would not “jump back and forth” between two consciousnesses. For other people, both hemispheres are you and are equivalent; while for you, perhaps you can only control half the body, and the one controlling the other half is another “guy.” I also want to ask a question I myself cannot figure out—if after split-brain surgery one of my hemispheres were accidentally “to die,” then am “I” “still alive,” or “half dead,” or “50% likely dead, 50% likely alive”?
If in the future there were a technology that could temporarily freeze the corpus callosum, cutting off the connection between the two hemispheres, and then “revive” the corpus callosum several years later, what kind of situation would appear? The stream of consciousness should reunite into one again; how would this person come to accept that he once had been two mutually independent conscious beings?
In this chapter I have raised many questions, yet I am unable to give explanations—these questions are difficult even for the most top-notch philosophers and psychologists to make coherent. But we can all think about these questions; everyone will have their own conclusion. I have only demonstrated one fact—that the mental world is mysterious, that consciousness is not as simple as “a function of the human brain”; it is also full of unsolved mysteries. The inquiry into the essence of mind has by no means ended, and for a long time to come, both now and in the future, it will still remain one of the themes of research and debate in philosophy.
[①]More precisely, “orthogonal universes”
[②]The Wernicke area is responsible for understanding language, and the Broca area for forming language
[③]For some reason, only smell is left hemisphere to left nostril, right hemisphere to right nostril. Vision is also not the left hemisphere controlling the right eye and the right hemisphere controlling the left eye; rather, the left hemisphere is responsible for the right side of the visual field of both eyes, and the right hemisphere is responsible for the left side of the visual field of both eyes.
[④]If it is a child, the chance of learning is quite high.
Translated from the Chinese original with AI assistance. The original text is authoritative.
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