In a 1975 study, psychologists Fergus Craik and Endel Tulving investigated which type of encoding results in the best memory for verbal information. In their experiment, participants were shown words and asked questions designed to engage one of three processing levels. Visual processing was prompted by questions about the physical appearance of the letters (e.g., font), acoustic processing by questions about the word's sound (e.g., rhyming), and semantic processing by questions about the word's meaning. Afterward, participants were given a surprise recall or recognition test for the words.