The cognitive architecture of processes responsible to assess similarity and clarity in a comparison task

When asked to compare two stimuli, participants are on average faster to respond Same than Different, an effect coined the fast-same. The dual-process theory argues that information about similarity is processed in priority over any other type of information, causing the fast-same effect. We tested this serial architecture of cognitive processes using a double factorial paradigm, suitable for a Systems Factorial Technology (SFT) analysis. Twenty participants completed a task in which they compared two letters, which were varied on two dimensions: the similarity and the clarity of the letters. Their task was to indicate if the second letter was the Same as the second letter (ranging from identical and clear to similar and slightly blurry) or if it was Different (if the stimuli were either dissimilar or very blurry). The SFT results show that most participants processed the information in serial, but in a mixed order. In other words, for some trials, participants processed similarity first, and for some other trials, they processed clarity first. This implies that participant indeed processed information in serial in the comparison task, but that it does not cause the fast-same effect.