Reading "glasses" will prime "vision," but reading a pair of "glasses" will not

In a lexical decision task with two primes and a target, the target was preceded 300 msec by the second prime (P2) which in turn was preceded by a brief forward and backward masked first prime (P1). When P1 and P2 were unrelated, reaction times were faster when the target was related to P2 (e.g., wave SALT ... pepper) than when the target was unrelated to P2 (and P1--e.g., wave LOAN ... pepper). However, this semantic priming effect was reduced to statistically nonsignificant levels when P1 and P2 were repetitions of the same word. That is, priming did not occur for salt SALT ... pepper relative to loan LOAN ... pepper. This reduction in priming was observed whether P2 and the target were strongly or weakly related. These findings raise problems for current accounts of semantic priming.