What sort of details outside of yourself are you best at noticing or picking up on? I guess the extraverted functions are best for that. My Si seems to only pick up details as they relate to myself - otherwise I can be oblivious. I can be with someone a whole day and not be able to tell you what the person was wearing at the end of it - unless something about their clothes specifically grabbed my attention. I'm always aware of what's going on around me, but unless there's the need to react to something, the details just sort of continue past me. If they're not needed in the present, I guess they don't really register.
On the other hand, the things that I do immediately pick up on and remember without having to concentrate are people's emotions, looks, gestures - that sort of thing. The other day, some people came around to see my flatmates who were out. I told the people they weren't in, and they left without leaving a message. Later on, one of my flatmates was trying to work out who the people would have been - asking me questions about them. I said they were a couple with a little boy - then I thought that perhaps they had a girl, not a boy - couldn't remember which. I tried to picture the child in my head, but nothing came up. Then I started wondering if I had imagined that they had a child. Because there was a pram just outside the door - maybe seeing the woman standing next to the pram made me make the connection? lol Then my flatmate wanted to know what the woman looked like - was she huge? Uh, Idk - I was looking at her face. lol What I did remember clearly about the situation was that she looked confused and uncomfortable to see me open the door - don't know why - and the guy looked a bit grumpy. lol I would be a terrible witness.
So what sort of things do you tend to notice without trying?