No abstract

A principal function of the medial frontal cortex, in particular the anterior cingulate cortex (ACC), is to monitor action. The error-related negativity (ERN, or N(E)), an event-related brain potential, reflects medial frontal action-monitoring processes. Specifically, the error-detection theory of the ERN states that the ERN reflects ACC processing that is directly related to detecting the error. This theory predicts that ERN and ACC activity should increase directly with the dissimilarity of the error from the correct response, with similarity defined with respect to the common movement features of the responses. In contrast, the conflict-detection theory claims that ACC and ERN activity represent the detection of response conflict. This theory predicts that the activity should increase directly with the similarity of the error and the correct response. To test these theories, we investigated the effects of response similarity and conflict on the ERN, using a task that involved hand and foot movements. ERN activity was largest under conditions of high response conflict, where the error was similar to the correct response. This finding favors the conflict-detection theory over the error-detection theory, although the ERN was not associated with posterror slowing, as predicted by proponents of both theories. Discrepancies between our results and those of past studies may stem from the use in previous studies of four-finger response tasks which are subject to unique physiological and biomechanical constraints. We conclude that the ERN reflects medial frontal activity involved in the detection or affective processing of response conflict.

Is content addressable in the representation that subserves performance in multiple-object-tracking (MOT) experiments? We devised an MOT variant that featured unique, nameable objects (cartoon animals) as stimuli. There were two possible response modes: standard, in which observers were asked to report the locations of all target items, and specific, in which observers had to report the location of a particular object (e.g., "Where is the zebra?"). A measure of capacity derived from accuracy allowed for comparisons of the results between conditions. We found that capacity in the specific condition (1.4 to 2.6 items across several experiments) was always reliably lower than capacity in the standard condition (2.3 to 3.4 items). Observers could locate specific objects, indicating a content-addressable representation. However, capacity differences between conditions, as well as differing responses to the experimental manipulations, suggest that there may be two separate systems involved in tracking, one carrying only positional information, and one carrying identity information as well.

Observers in a multiple object tracking task can track about four to five independently moving targets among several moving distractors, even if all of the stimuli disappear for a 300-msec gap. How observers reacquire targets following such a gap reveals what kind of information they can maintain for targets. Previous research has suggested that participants maintain minimal information about a set of moving objects-namely, just their present spatial locations. We report five new experiments that demonstrate retention of location information for at least four objects, and extrapolated motion information for around two objects.