Presentation for 2006 Meeting of the Society for Neuroscience

Sustained attention is essential for many cognitive behaviors, including performance in the multiple object tracking (MOT) paradigm, which relies almost completely on attention (Pylyshyn and Storm, 1988). Using MOT, parametric increases in fMRI activation as a function of attentional load have been found in both parietal and frontal brain areas, but the results lacked information about the temporal course of attention (Culham et al., 2001).

With high-density electrode arrays, we used electroencephalograpy (EEG) to examine the temporal dynamics of attention during multiple object tracking. Subjects viewed ten discs moving randomly on a display, and attentively tracked a pre-cued subset of the discs. Attentional load was operationalized as the number of discs (two to four) that had to be tracked. We were interested in changes in oscillatory power over the course of attentive tracking, as changes in the alpha (8-13 Hz) and gamma (20-50 Hz) bands are correlated with intensity of visual attention (Klimesch, 1999; Gruber, 1999; Muller, 2000).

We found that alpha power at parietal electrodes decreased as MOT attentional load increased. Moreover, this decrease grew more pronounced over the course of the tracking period. Although in the low-load condition, alpha power showed little change with time, in the more demanding conditions, alpha power decreased with time on task. Gamma power at many electrode sites decreased with tracking time as well, but this effect was not load sensitive. These results reveal EEG correlates of attentional load dependent and independent activation, and also demonstrate that visual attention is a dynamic process, which is constrained not only by spatial capacity, but also by temporal limitations.

Supported by NIH grants MH068404.