Abstract
The item-specific proportion congruency (ISPC) effect constitutes the phenomenon that Stroop effects are reduced when incongruent items belong to a mostly-incongruent (MI) than a mostly-congruent (MC) grouping. While the ISPC effect is purported to reflect associations formed in long-term memory, the assigned proportion manipulation entails that stimulus repetitions vary as a function of the MC and MI conditions, leaving open the possibility that a short-term repetition priming process may work to enlarge the Stroop effect in the MC relative to the MI group. In the present study we investigated whether the ISPC effect reflected contributions from separate long-term associative learning and short-term repetition priming processes. To do so, the magnitude of the ISPC effect was compared when stimulus repetitions were systematically present and absent across the experimental session. While we observed that the ISPC effect was robust across groups, it was revealed that removing stimulus repetitions significantly attenuated the effect. Additionally, it was revealed that stimulus repetitions had a profound impact on performance, and sequential congruency (i.e., congruent-to-congruent and incongruent-to-incongruent inter-trial repetitions) had none, suggesting that this repetition priming process depended on the repetition of stimulus features. Overall, the present study indicates the typical ISPC effect reflects contributions from both short and long-term memory processes.