Building permanent memory codes: codification and repetition effects in word identification.

Abstract

The studies presented in this article investigate the memory processes that underlie two phenomena in threshold identification: word superiority over pseudowords and the repetition effect (a prior presentation of an item facilitates later identification of that item). Codification (i.e., the development of a single memory code that can be triggered even by fragmented input information) explains the faster and more accurate identification of words than pseudowords. Our studies trace the development and retention of such codes for repeated pseudowords and examine the growth and loss of the repetition effect for both pseudowords and words. After approximately five prior occurrences, words and pseudowords are identified equally accurately in two types of threshold identification tasks, suggesting codification has been completed for pseudowords. Although the initial word advantage disappears, the accuracy of identification still increases with repetitions. The facilitation caused by repetition is not affected much by spacing within a session, but drops from one day to the next, and after a delay of one year has disappeared (new and old words were identified equally well). These results suggest an episodic basis for the repetition effect. Most important, after one year, performance is equal for old pseudowords and new and old words: all these levels are superior to that for new pseudowords, suggesting that the learned codes for pseudowords are as strong and permanent as the codes for words. A model of identification is presented in which feedback from codes and episodic images in memory facilitates letter processing. An instantiation of the model accounts for the major features of the data.