Priming
Priming is an increase in the speed or accuracy of a decision that occurs as a consequence of a prior exposure to some of the information in the decision context, without any intention or task related motivation. Since priming occurs in tasks where memory for previous information is not required, and may even have detrimental effects, it is assumed to be an involuntary and perhaps unconscious phenomenon. One of the original demonstrations (Meyer and Schvaneveldt, 1971) of priming occurred in a lexical decisiontask in which a series of decisions is made about whether letter strings are words or not. Priming was shown to occur in cases where two successive letter strings were semantically related words. For example the decision that 'doctor' is a word was faster when the preceding letter string was 'nurse' as compared to 'north' or the non-word 'nuber'. This semantic priming effect was explained by a mechanism termed spreading activation that had been proposed by Collins and Loft us in a 1975 paper that updated the concepts originally set out by Collins and Quillian. In this new view semantic memory was based on a network that was not strictly hierarchical and for which intersection search was not a suitable search mechanism. Instead Collins and Loftus proposed when the memory representation for a concept is activated the activation spreads to neighboring stored representations. If such a neighbor is presented as the next letter string in a lexical decision (or other) task, it will be identified sooner because it was partially activated by the prime word even before being presented. An underlying assumption is that related words are stored nearer one another (as in Collins and Quillian) than unrelated so that priming is proportional to semantic relatedness. It is important to note that priming occurs in the lexical decision task even though that task does not require participants to remember or use information about letter strings from the previous trials. Priming is therefore believed to occur without intention and is described as an 'automatic' process. It also seems to occur without awareness and is therefore described as an 'unconscious process'. These characteristics distinguish priming from aspects of memory involving deliberate retrieval as used in most episodic memory tests. As is explained below, in the view of many theorists priming and episodic retrieval are actually examples of two different kinds of memory: implicit and explicit memory.
