Within-trial and across-trial distractor rejection mechanisms.

Color singleton distractors' interference is known to be modulated by rejection mechanisms based on the distractors' probability of occurrence at different locations. Here, to further address color-singleton distractor rejection, we used a modified version of the additional-singleton paradigm, where four consecutive displays were presented in rapid succession on each trial. In Experiment 1 the irrelevant singleton was either presented in the last display (single location, 40% probability) or repeated in all four displays (repeated location, 10% probability), with the two conditions appearing at separate locations. Contrary to common observations, we found that capture was much more attenuated at the repeated location, despite the lower distractor probability. Furthermore, we found no signs of target-processing impairment at the repeated location where capture was basically eliminated, whereas capture was present at the single location. In Experiment 2, where both locations had repeated distractors, we found target-processing impairment only at the location with the highest distractor probability (40%). Experiment 3 indicated that suppression, regardless of any within-trial distractor repetitions, becomes evident only when the distractor probability is high enough (35%). Experiment 4 replicated the main findings in a single experiment, within the same group of participants. The results suggest the possible existence of distinct rejection mechanisms based on within-trial and across-trials distractor repetitions. While suppression is probably involved in the across-trials rejection mechanism, we propose that the one operating on a shorter within-trial time scale is likely controlled solely by a distractor-expectation or distractor-prediction error mechanism.