The upcoming Samsung 400 Hz (or 480 Hz in the US.) utilizes the so-called BFI/DFI principle. BFI/DFI stands for (Black/Dark Frame Insertion), and means that the TV inserts very short black frames between the original picture frames.
The method utilizes the principle that the human eye does not “forget” light instantly. You know this from a very short flash that tends to stay on your eye cornea for a short time. By inserting very short black images between the other frames, you can constantly reset the human eye, in order to improve the perception of response time on a LCD-TV.