Explicit and implicit intermixed-blocked effects in the absence of instructions requiring the search for differences between visual stimuli.

In three experiments, participants were asked to mentally count how many target stimuli appeared in a sequence of presentations, without informing them that there were two types of stimuli (AX and BX) with a specific difference. Some participants received intermixed AX and BX presentations (INT groups), while others received the presentations in blocks (BLK groups). In all three experiments, the INT group showed a greater ability to differentiate the stimuli in a posttest compared to the BLK group. In Experiment 1a, where AX and BX were drawings of plants that differed in the number of petals, the improvement in differentiation was accompanied by the ability to identify the specific difference. However, in Experiments 1b and 2, where AX and BX were robots with a more subtle difference in eye separation, the improvement in differentiation occurred without participants being able to indicate what the difference between the stimuli was. These results suggest that intermixed preexposure can generate, without the need for initial instructions to look for differences between stimuli, both explicit (Experiment 1a) and implicit (Experiments 1b and 2) beneficial effects on stimulus differentiation. (PsycInfo Database Record (c) 2025 APA, all rights reserved).