Memory blocks in word fragment completion caused by involuntary retrieval of orthographically related primes

Seven experiments showed that word fragments are not solved as well following prior exposure to orthographically similar primes (e.g., ANALOGY as a prime for A_L__GY) relative to orthographically dissimilar primes (e.g., UNICORN). This blocking effect was influenced by the modality (auditory vs. visual) of the primes but not by the depth to which they were processed. This blocking effect occurred even when participants were informed about it and told to try to avoid remembering the primes, and it was not affected by the proportion of test fragments for which the orthographic primes were correct versus incorrect answers. The results have implications for theories concerned with unconscious mechanisms that underlie memory blocking and blocks to creative problem solving.