<p>Four experiments assessed the effect of practice with similar stimuli on the ability of adult humans to identify a target stimulus by means of same/different judgments. Experiment 1 found the target identification task sensitive to the effect of practice, by showing a decrement in the percentage of errors across blocks of trials. Experiment 2 also found the task to be sensitive to stimulus length and distinctiveness, as there were more errors with long than short stimuli, and there were also more errors when the stimuli contained a higher number of shared elements. Experiments 3 and 4 found a progressive decrement of errors on the “same” trials but not on the “different” trials, suggesting an increment in the ability to judge the target stimulus as same, although accuracy to judge the non-target stimuli as different was not improved to the same extent. It appeared to be the case that these findings were not related to any potential response bias to judge the stimuli as same or different. The study found the target identification task sensitive to variables related to perceptual learning, providing some new insights about the potential biases to respond same or different.</p>