On the additive effects of stimulus quality and word frequency in lexical decision: evidence for opposing interactive influences revealed by RT distributional analyses

The joint effects of stimulus quality and word frequency in lexical decision were examined in 4 experiments as a function of nonword type (legal nonwords, e.g., BRONE, vs. pseudohomophones, e.g., BRANE). When familiarity was a viable dimension for word-nonword discrimination, as when legal nonwords were used, additive effects of stimulus quality and word frequency were observed in both means and distributional characteristics of the response-time distributions. In contrast, when the utility of familiarity was undermined by using pseudohomophones, additivity was observed in the means but not in distributional characteristics. Specifically, opposing interactive effects in the underlying distribution were observed, producing apparent additivity in means. These findings are consistent with the suggestion that, when familiarity is deemphasized in lexical decision, cascaded processing between letter and word levels is in play, whereas, when familiarity is a viable dimension for word-nonword discrimination, processing is discrete.