Repetition priming effects in lexical decision tasks are stronger for low-frequency words than for high-frequency words. This frequency attenuation effect creates problems for frequency-ordered search models that assume a relatively stable frequency effect. The suggestion is made that frequency attenuation is a product of the involvement of the episodic memory system in the lexical decision process. This hypothesis is supported by the demonstration of constant repetition effects for high-and low-frequency words when the priming stimulus is masked; the masking is assumed to minimize the influence of any possible episodic trace of the prime. It is further shown that long-term repetition effects are much less reliable when the subject is not required to make a lexical decision response to the prime. When a response is required, the expected frequency attenuation effect is restored. It is concluded that normal repetition effects consist of two components: a very brief lexical effect that is independent of frequency and a long-term episodic effect that is sensitive to frequency.There has been much recent interest in the fact that in a lexical decision experiment, where subjects are required to classify letter strings as words or nonwords, there is a substantial increase in both the speed and the accuracy of classification for words that are presented more than once during the experiment, even though considerable time may have elapsed between successive presentations (Forbach, Stanners, & Hochhaus, 1974;Kirsner & Smith, 1974; Scarborough, Cortese, & Scarborough, 1977). This phenomenon is referred to as the repetition effect.There are basically two different approaches to the repetition effect. On the one hand, it is seen as the product of a temporary modification to the process of lexical access (e.g., Forbach et al., 1974). As a result of recent activation, the lexical representation of a word is left in a state of increased accessibility. This priming effect can then be used as a powerful diagnostic tool for analyzing the

Form-priming occurs when a prime that is graphemically similar to the target word facilitates processing of the target. In an activation model (such as Morton's logogen model), such an effect can be interpreted as a partial-activation effect. A prime that shares letters with the target must inevitably produce activation in the detectors for both the prime and the target. Alternatively, form-priming could be seen as a special case of repetition-priming, in which the prime actually accesses the entry for the target. It is shown that masked-priming effects in the lexical decision task can be obtained for graphemically related pairs such as bontrast-CONTRAST, but not for four-letter pairs such as bamp-CAMP. It is suggested that the priming effect is controlled by neighbourhood density, short words usually having many neighbours, long words having very few. This hypothesis is supported by the finding that form-priming does occur for four-letter words if the prime and target are drawn from low-density neighbourhoods. For a partial-activation theory, an inhibitory mechanism that is sensitive to the number of prime-neighbours is required to explain the results. Of the several versions of a repetition account considered, the “best match” hypothesis appears to be the most promising: this assumes that priming is limited to the stimulus that best matches the prime. It is also shown that prime-target pairs that are related in form and meaning (e.g. made-MAKE) produce the same priming effect as identical pairs, as predicted by a repetition account that assumes a common entry underlying both forms.

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