Electrophysiological measures of attentional tracking and working memory
Drew, Trafton, 1980-
In the multiple object tracking (MOT) task, observers are presented with multiple identical objects, some of which are temporarily identified as targets. After a selection period, all objects move randomly and independently for several seconds. At the end the motion period, all objects stop and observers must identify the target objects again. This task has been used to study a variety of important cognitive questions from object-based attention to cognitive development, divided attention and the development of expertise. Yet, surprisingly little is known about the neural mechanisms that underlie the ability to track multiple targets independently. Although a number of researchers have used fMRI (functional magnetic imaging) to examine what areas are active during MOT, the current set of studies is the first to employ ERPs (event-related potentials) to examine the neural mechanisms of MOT. With excellent temporal resolution, the ERP methodology allows researchers to delineate the time course of different phases of a single task with millisecond precision, something not possible with fMRI. In Chapter II, we manipulated the number of targets and difficulty of tracking and observed a lateralized contralateral negativity that was sensitive to the number of targets but not difficulty of tracking. Chapter III examined the effect of irrelevant white probes flashed briefly throughout the trial while observers tracked. We observed modulations of early visual components that indicated that during tracking, spatial attention focused on targets but did not differentiate between distractors and empty space. Finally, in Chapter IV, we examined the relationship between visual working memory (VWM) and MOT by manipulating the presence or absence of task relevant motion. We found that the waveforms evoked by an MOT task in the absence of task-relevant motion were nearly identical to waveforms evoked by the VWM task, suggesting that VWM is an important part of the typical MOT task. This thesis includes previously published and unpublished material.