An RT distribution analysis of relatedness proportion effects in lexical decision and semantic categorization reveals different mechanisms

The magnitude of the semantic priming effect is known to increase as the proportion of related prime–target pairs in an experiment increases. This relatedness proportion (RP) effect was studied in a lexical decision task at a short prime–target stimulus onset asynchrony (240 ms), which is widely assumed to preclude strategic prospective usage of the prime. The analysis of the reaction time (RT) distribution suggested that the observed RP effect reflected a modulation of a retrospective semantic matching process. The pattern of the RP effect on the RT distribution found here is contrasted to that reported in De Wit and Kinoshita’s (2014) semantic categorization study, and it is concluded that the RP effect is driven by different underlying mechanisms in lexical decision and semantic categorization.