Quantifying the time course of similarity

Does the similarity between two items change over time? Previous studies (Goldstone & Medin, 1994; Gentner & Brem, 1999) have found suggestive results but have relied on interpreting complex interaction effects from “deadline” decision tasks in which the decision making process is not well understood (Luce, 1986). Using a self-paced simple decision task in which the similarity between two items can be isolated from strategic decision processes using computational modeling techniques (Ratcliff, 1978), we show strong evidence that the similarity between two items changes over time and shifts in systematic ways. The change in similarity from early to late processing in Experiment 1 is consistent with the theory of structural alignment (Gentner, 1983; Goldstone & Medin, 1994), and Experiment 2 demonstrates evidence for a stronger influence of thematic knowledge than taxonomic knowledge in early processing of word associations (Lin & Murphy, 2001).