There are several proposed theories regarding the N400 in a priming paradigm and the most favored one is from Neely and Keefe (1989), who propose that these mechanisms are automatic spreading activation (Collins and Loftus, 1975), expectancy and semantic matching (den Heyer et al., 1983; Neely and Keefe, 1989; Silva-Pereyra et al., 1999). Expectancy and semantic matching mechanisms are referred to as controlled priming mechanisms and are generally believed to act more effectively at relatively long stimulus onset asynchrony (SOA) of greater than 500 ms, whereas automatic spreading activation mechanism is said to have influence on the priming effect at short SOAs (De Groot et al., 1986; Neely, 1991). However, studies have shown that semantic matching strategies (controlled priming mechanisms) can be active at SOAs as short as 150 ms (Koivisto, 1998) and automatic spreading activation can influence priming as long as 2000 ms (Deacon et al., 1999). In general, research evidence suggests that the N400 in priming paradigms reflects different mechanisms, such as automatic spreading activation (Deacon et al., 2004; Deacon et al., 2000; Kiefer, 2002; Kiefer and Spitzer,
