What is your self, really? And also, I guess, when Spider-Man puts on the black suit, does he change into a different person?
No. That isn’t me giving an answer because I think it’s obvious, and it isn’t the answer the essay gives, either. The essay references the black suit’s effects on Spider-Man a lot, but never actually makes the argument that Spider-Man becomes a different person by putting on the black suit. It kind of implies it will at some point, but then it doesn’t.
But what is your self? Your emotions? In practice, we tend to refer to our emotions as things that happen to us, and to which we can be prone, but not really what we are. You do not become a literally different person because you are angry. Your thoughts? How does that work? Do you cease to be every time one thought completes and another begins? Memories? But we don’t usually think of amnesiacs as being a new person walking around in the old one’s body, but rather as someone who can’t remember who they used to be.
The essay wanders around talking about biopsychosocial connections, but ultimately the answer here is that your self is the persistent consciousness which experiences things. Peter Parker and Eddie Brock both are the same guy before and after bonding with the symbiote, because their consciousness has not ceased. This is kind of a cop-out answer, though, because we have no idea what the consciousness is, where it comes from, and can’t even prove that there’s more than one. I know that I am conscious and experience things, but I don’t know if anyone else does. Presuming you are, in fact, conscious, you know that you are conscious, but you don’t know for sure if I am. I assume you’re conscious because you behave more or less the same way I do, so I expect you have that quality in common with me as well, but there’s nothing I can measure to know for sure, and indeed it’s not clear how I could possibly test that, or you test me for my consciousness.
Punting to consciousness is kind of like punting to quantum physics, in that it’s an unknown thing that could therefore theoretically be responsible for anything, but in this case it really is most consistent with how people use the concept of “self.” It’s just not a very satisfying answer, because we understand almost nothing about it.