I feel awkward saying anything with absolute certainty, because this is a question I ponder myself a lot too. I have a hard time because I am an only child, and now it's hard to tell if I'm an Extravert with massive Introvert-like coping mechanisms from growing up and having to entertain myself, or if I'm simply an Introvert. It doesn't help that there appear to be multiple definitions of Introvert/Extravert, lol.
This is a pretty simple-minded explanation, but whatevs.
In general, Ne/Ti will intuit the possibility in a situation, and then default to Ti to strategize how to bring it about. They look to reality first, realize the possible ways of changing it, and then logically work out how to make it real.
Ti/Ne is the other way around. They first attempt to understand the whole structural pattern that underlies a situation, and then use Ne to get a gist of what their understanding's impact on reality would be. They're more into discerning patterns and then working out their implications without necessarily altering reality.
If you want, I have a ton of info in my PM Inbox I could forward you, too.
Also, since I'm kinda-sorta in the same conundrum as you: read about Ti from a reputable source. Since I've been reading about Ti from legit sources of information, I've learned a lot, and a lot of what I would've guessed was Ne in myself was really Ti. It's an odd function, and there's a ton of stereotypes and misinformation about it on the net.