Priming is an implicit memory effect in which exposure to one stimulus influences a response to another stimulus. People are faster in deciding that a string of letters is a word when the word followed an associatively or semantically related word. For example, NURSE is recognized more quickly following DOCTOR than following BREAD. Various experiments supported the theory that activation spreading among related ideas was the best explanation for the facilitation observed in the lexical decision task. The priming paradigm provides excellent control over the effects of individual stimuli on cognitive processing and associated behavior because the same target stimuli can be presented with different primes. Thus differences in performance as a function of differences in priming stimuli must be attributed to the effect of the prime on the processing of the target stimulus. Priming can occur following perceptual, semantic, or conceptual stimulus repetition. For example, if a person reads a list of words including the word table, and is later asked to complete a word starting with tab, the probability that he or she will answer table is greater than if they are not primed. Another example is if people see an incomplete sketch they are unable to identify and they are shown more of the sketch until they recognize the picture, later they will identify the sketch at an earlier stage than was possible for them the first time. The effects of priming can be very salient and long lasting, even more so than simple recognition memory.] Unconscious priming effects can affect word choice on a word-stem completion test long after the words have been consciously forgotten.[ Priming works best when the two stimuli are in the same modality. For example visual priming works best with visual cues and verbal priming works best with verbal cues. But priming also occurs between modalities,] or between semantically related words such as "doctor" and "nurse".