Other evidence comes from experimental studies showing that some manipulations (e.g., a distractor task, such as repeatedly subtracting a single-digit number from a larger number following learning; cf Brown-Peterson procedure) impair memory for the 3 to 5 most recently learned words of a list (it is presumed, still held in short-term memory), while leaving recall for words from earlier in the list (it is presumed, stored in long-term memory) unaffected; other manipulations (e.g., semantic similarity of the words) affect only memory for earlier list words, but do not affect memory for the last few words in a list.