a string of letters, usually four or five, is flashed for several milliseconds onto a screen. readers are then asked to choose which of two letters had been in the flashed string. for example, if "wosk" had been flashed, a reader might have to decide whether "k" or "h" had been in "wosk". a wse arises when subjects choose the correct letter more consistently when letter strings are real words rather than nonwords (e.g. "wkrg") or single letters.