Yours vs. Mine
A question that inevitably comes up very early in the process of designing a new app is this: should the interface refer to the user as “your” or “my” when talking about the user's stuff, as in “my profile” or “your settings”? For a long time, this question ate at my soul. Which is right?
The answer actually has quite a few implications, even if they're subconscious. If you refer to a user's profile as “your profile,” the implication is that the interface is communicating with you, whereas if you refer to it as “my profile,” you're implying that the interface is an extension of the user, as though it is communicating for you.
There are two groups of neurological adaptations that I think might roughly support each of the approaches.
As humans have evolved the ability to use tools, the brain has developed a function for assimilating external objects into its motor mapping. After using a hammer for a while, your body starts to build systems that treat the hammer like an external appendage, or at least an extension of your existing appendages. In fact, these on-the-fly mappings can even replace your actual arm: When test subjects are shown a fake arm that replaces their real arm (using mirror magic), a researcher can make them flinch in pain by poking the fake arm with a pin.
If we refer to the user's stuff as “my stuff,” we're potentially using this artificial mapping system by assuming the brain has assimilated the interface into its existing spacial mapping. In that case, calling a part of that interface “mine,” as though it already belongs to me, makes sense, because my brain considers it a literal extension of myself.
On the other hand, humans are social creatures and we've evolved extremely complex systems for social interaction with other humans. There are entire areas of the human brain dedicated to understanding, interpreting, creating, and analyzing language. When we talk with people, we have a very constant, strict set of absolutes that guide us through sorting out our thoughts: There is me, and I am communicating with a series of other people called “you”.
Additionally, we've evolved systems for making estimations and assumptions about what other people are actually trying to communicate despite the actual words that come out of their mouths. These assumptions help us to limit explicitness and increase efficiency in social interactions.
If we think about interfaces as literal “interfaces” to tasks (like how people are interfaces to their ideas), instead of as tools themselves, it makes sense for the interface to take on a personality, and to become a “you” to the user. Thus, it would make sense for the interface to refer to a user's stuff as “your stuff,” because the interface is just a medium between the user and what she wants to accomplish or find. In a way, the interface takes on a social characteristic, and becomes a humanoid assistant by utilizing existing functions of the human brain's social systems.
After thinking about this stuff for a very long time, I've settled pretty firmly in the camp of thinking that interfaces should mimic social creatures, that they should have personalities, and that I should be communicating with the interface rather than the interface being an extension of myself. Tools have almost always been physical objects that are manipulated tactually. Interfaces are much more abstract, and much more intelligent; they far more closely resemble social interactions than physical tools.
The answer for me, then, is that you're having a conversation with the interface. It's “Your stuff.”