The Nature of Consciousness: Consciousness, Life and Meaning

Identity: Who Am I?

Every year 98% of the atoms of my body are replaced: how can I claim to be still the same person that I was last year, or, worse, ten years ago? About 70% of your original neurons die before you reach maturity: what is the relationship between you and the child that had all those dead neurons? What is (where lies) my identity? What is "my" relationship to the metabolism of my body?

Derek Parfit once proposed this thought problem: what happens to a person who is destroyed by a scanner in London and rebuilt cell by cell in New York by a replicator that has received infinitely detailed information from the scanner about the state of each single cell, including all of the person's memories? Is the person still the same person? Or did the person die in London? What makes a person such a person: bodily or psychological continuity? If a person's matter is replaced cell by cell with equivalent cells is the person still the same person? If a person's psychological state (memory, beliefs, emotions and everything) is replaced with an equivalent psychological state is the person still the same person? What if the original is not destroyed, and now there is a perfectly identical copy of yourself living in London? Are both you?

Parfit believes that teleportation is simply a way for the self to travel from New York to London: yes, you are the same person at the other end. On the other hand, you die all the time because your brain changes all the time, and your self now is not the same self of a few minutes ago. And since you died all the time that you thought you were living, the final death is not a big deal: it is just one more death in a long sequence of deaths, or, better, it is yet another self that dies.

This is not just philosophy for the sake of philosophy: your morality depends on what you think "you" is. If you think of yourself as a continuous being, you reach some conclusions. If you think of yourself as identical to your brain, and therefore dying and being born another person all the time, you reach different conclusions on what is right and what is wrong. Your rational and emotional behavior depend on that assumption.

The most obvious paradox is: how can reality be still the same as we grow up? Do two completely different brains see the same image when they are presented with the same object? If the brains are different, then the pattern of neural excitement created by seeing that object will be different in the two brains. How can two different brains yield the same image? The logical conclusion is "no, the tree I see is not the tree you see, we just happen to refer to it the same way so it is not important what exactly we see when we look at it". But then how can I see the same image yesterday, today and tomorrow? Our brain changes all the time. Between my brain of when i was five years old and my brain of today there is probably nothing in common: every single cell has changed, connections have changed, the physical shape of the brain has changed. The same object causes a different neural pattern in my brain today than it did in my brain forty years ago. Those are two different brains, made of different cells, organized in different ways: the two patterns are physically different.

Nonetheless, it appears to me that my old toys still look the same. But they shouldn't, because my brain changed, and the pattern they generate in my brain has changed: what i see today should be a different image than the one i saw as a five-year old. How is it that i see the same thing even if i have a wildly different brain?

Furthermore, experience molds the brain: i am not only my genome, i am also the world around me. And i change all the time according to what is happening in the world. "I am" what the world is doing.

All of this almost seems to prove that "i" am not in my brain, that there is something external to the brain that does not change over time, that the brain simply performs computations of the image but the ultimate "feeling" of that image is due to a "soul" that is external to the brain and does not depend on cells or connections.

On the other hand, it is easy to realize that what we see is not really what we think we see.

When we recognize something as something, we rarely see/feel/hear/touch again exactly the same thing we already saw/felt/heard/touched before. I recognize somebody's face, but that face cannot possibly be exactly the same image i saw last time: beard may have grown, a pimple may have appeared, hair may have been trimmed, a tan may have darkened the skin, or, quite simply, that face may be at a different angle (looking up, looking down, turned half way). I recognize a song, but the truth is that the same song never "sounds" the same: louder, softer, different speakers, static, different echo in the room, different position of my ear with respect to the speakers. I recognize that today the temperature is "cold", but if we measured the temperature to the tenth decimal digit it is unlikely that we would get the exact same number that i got the previous time i felt the same cold. What we "recognize" is obviously not a physical quantity: an image, a sound, a temperature never repeat themselves. What is it then that we recognize when we recognize a face, a song or a temperature? Broadly speaking, it is a concept.

We build concepts of our sensory experience, we store those concepts for future use, and we match the stored concepts with any new concept. When we do this comparison, we try to find similarity and identity. If the two concepts are similar enough, we assume that they are identical, that they are the same thing. If they are not similar enough, but they are more similar than the average, then we can probably establish that they belong to a common super-concept (they are both faces, but not the same face; they are both songs, but not the same song; and so forth). We have a vast array of concepts which are organized in a hierarchy with many levels of generalization (“your face” to “face of you and siblings” to “faces of that kind” to “generic face” to ... to “body part” to ...). A sensory experience is somehow translated into a concept and that concept is matched with existing concepts and eventually located at some level of the hierarchy of concepts. If it is close enough to an existing concept of that hierarchy at that level, it is recognized as the same concept. Whatever the specific mechanism, it is likely that what we recognize is not a physical quantity (distribution of colors, sound wave or temperature) but a concept, that somehow we build and compare with previously manufactured concepts.

Identity is probably a concept. I have built over the years a concept of myself. My physical substance changes all the time, but, as long as it still matches my concept of myself, I still recognize it as myself.

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