The Direct Route: Mediated Priming in Semantic Space
McKoon and Ratcliff (1992) presented a theory of mediated priming where the priming effect is due to a direct but weak relatedness between prime and target. They also introduced a quantitative measure of word relatedness based on pointwise mutual information (Church and Hanks; 1990), and showed that stimuli chosen with the measure produced graded priming effects as predicted by their theory. Using stimuli from Balota and Lorch (1986), Livesay and Burgess (Livesay and Burgess; 1997, 1998) replicated the mediated priming effect in humans, but found that in HAL, a corpus-derived semantic space (Lund, Burgess and Atchley; 1995), mediated primes were in fact further from their targets than unrelated words. They concluded from this that mediated priming is not due to direct but weak relatedness. In this paper we present an alternative semantic space model based on earlier work (McDonald and Lowe; 1998). We show how this space allows a) a detailed replication of Ratcliff and McKoon's experimental results using their stimuli and b) a replication of Livesay and Burgess's human experimental results showing mediated priming. We discuss the implications for McKoon and Ratcliff's theory of mediated priming.