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The Same-Different task consists of a rapid presentation of two stimuli and is used to assess how quickly humans can distinguish between identical and non-identical stimuli. Despite the task’s simplicity and benefitting from over 50 years of research, there are still major gaps in the models that try to explain the cognitive process required to make comparison judgements. A central modelling hurdle is the fast-same phenomenon, referring to the fact that “Same” responses are faster and more accurate than “Different” responses, whereas typical analytical-based models would predict the opposite. Nevertheless, some modelling propositions have been put forth, including Ratcliff and Hacker`s (1981) response bias framework. In this study, we diligently reproduced Experiment 1 of Ratcliff and Hacker's (1981) study to put their proposition to the test. This experimental study consists of two conditions: adding a caution component to “Same” responses in one case and to “Different” responses in the other. We observe that manipulating task instructions does not generate any significant difference between conditions and that there is no speed-accuracy trade-off, opposing Ratcliff and Hacker’s (1981) original results. Response bias could therefore not be the main explanation for the fast-same phenomenon.

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