What everyone said above, basically. I think INTPs are so wrapped up in themselves, they fail to notice or even care about others. No Fe.
I find that INTPs just talk at you and rarely try to engage you, or even care if you are engaged. When they see my eyes glaze over with boredom, they hardly notice and continue on rambling in detail, interjecting their own monologues to giggle at some random non-sequitor, go back to rambling and then stop to explain the whole history about a phrase they used before getting back to the once-interesting but now tedious topic. And they can really go on *forever* and never really get to the damn point. And get annoyed when you try to make them bring it on home.
I am always acutely aware of how I am being received. If I notice someone glance away for even a second, I speed up the explanation, change the subject or inject something humorous in to draw everyone back in and get everyone commenting and talking back.
Most times when I talk to an INTP, they don't appreciate back and forth banter - when they are on about a subject, they will never let you get a word in edgewise - *never*. The minute I open my mouth to respond after being silent for 15 minutes, I am immediately interrupted and spoken over. This is the only time I see INTPs get assertive and loud. It can be quite annoying.
My lovely, lovely INTP boyfriend often talks me to sleep on the phone, and continues speaking to me for 20-30 mins even though he knows I am fast asleep, bless his heart.