Prime relevance is a critical factor for lexical contribution to letter level processing.

When nonwords are intermixed with words in reading aloud, stimulus quality (SQ) and frequency exert additive effects. This pattern suggests that interactive activation between the letter level and the orthographic lexicon is strategically prevented to avoid lexical capture (O‘Malley & Besner, 2008). However, when a semantic priming paradigm is applied in lexical decision, frequency interacts with SQ for unrelated trials (Borowsky & Besner 1993). The aim of the present research is to asses the role of prime relevance in this effect. In Experiment 1, frequency, SQ and prime relatedness (repeated vs. unrelated) were manipulated in a reading task with words and nonwords. Interactive effects of frequency and SQ were observed. In Experiment 2 only unrelated primes were used, and additive effects of frequency and SQ were found. These results suggest that the presence of related primes plays a critical role in the regulation of activation dynamics in target processing.