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The Simon effect refers to the relatively poorer response times and accuracy when responding to targets that appear in a task-irrelevant spatial location that is incongruent with the location of the correct response key, compared with targets that appear in spatially congruent locations. Like Stroop and flanker effects, the Simon effect is thought to result from conflict between an irrelevant response tendency and an intended response. Because attentional control has been linked to conflict resolution, the Simon task has been proffered as a possible tool for measuring the efficacy of executive control mechanisms. These mechanisms are also involved in working memory (WM) processes, and are thought to be responsible for maintaining information in the presence of continued processing or distraction. The present study investigated the interface between WM and attention by examining the time course of the Simon effect over the response time distributions under varying WM load conditions. Participants completed verbal 0-back, spatial 0-back, verbal 2-back, and spatial 2-back tasks. Results show that the Simon effect is diminished in high WM load tasks compared with low-load tasks, and that the Simon effect interacts with the spatial task domain such that the effect persists across the distribution of response times. In contrast, the Simon effect peaks and decays in verbal tasks. The results demonstrate that the Simon effect interacts with WM load and task domain. The results suggest that the effect is more modifiable than expected, and support a complex interface between WM and attentional control. [ABSTRACT FROM AUTHOR]

Visual tracking abilities are limited to only a few objects at a time. When do errors arise? We hypothesized that some errors arise prior to tracking; specifically, during the first moments of a trial because of an inability to correctly perceive the number of targets in a display. To test this hypothesis, we modified a basic multiple object tracking (MOT) task in two ways: (1) we distilled the first moments of MOT into a static working memory task, requiring participants to remember and then identify targets among nontargets in displays without motion; (2) we unconstrained the number of responses a participant could make, asking them to terminate each trial when they felt that they had made an adequate number of responses. In Experiment I, participants made the wrong number of responses in a considerable number of trials, and they tendered the wrong number of responses more frequently with larger loads. Comparisons across different delay durations demonstrated that these results were not caused by temporal decay. Follow-up experiments produced similar results when participants stated the cardinal number of targets perceived in a static trial (Experiment 2), and when they reported whether or not a test display included the same number of targets as a memory display (Experiment 3). Finally, with a typical tracking duration, participants also produced the wrong number of responses frequently (Experiment 4). Thus, some of the difficulty associated with MOT originates from uncertainty about the number of targets at the start of an episode. [ABSTRACT FROM AUTHOR]