I've found recently that I can't get the chance to speak when I'm in a situation with more than one other person, especially a work meeting. In the second or two that I take to think about what's been said and consider what to say, someone else cuts in. More often than not, they just grab the chance to speak and say something not very important.
Now, I've always been kind of a slow one-to-one person, but I think it's been getting worse. I may be getting old and senile, but maybe it's the effect of too much written communication, like here. It encourages you to think at least a little bit before you contribute.