As I understand it, when they talk about 100 ms being the fastest possible thing we can notice, they mean if we can notice a reply from a computer was instantanious or if there was a delay. If we get to compare instantaneous to 10 ms lag in realtime sound, we can very easily hear the difference. But if we type a question to a computer and get a text answer within 100 ms we will persive it as being instantaneous.

http://theixdlibrary.com/pdf/Miller1968.pdf