Abstract
When attention is split into foci at disparate locations, the minimum size of the selection focus at each location is larger than if only one location is targeted (Franconeri, Alvarez, & Enns, 2007)- splitting attention reduces its spatial resolution. Here we tested temporal resolution and speed limits. STIMULUS. Three concentric circular arrays (separated by large distances to avoid spatial interactions between them) of identical discs were centered on fixation. Up to three discs (one from each ring) were designated as targets. The discs orbited fixation at a constant speed, occasionally reversing direction. After the discs stopped, participants were prompted to report the location of one of the targets. DESIGN. Across trials, the speed of the discs and the number in each array was varied, which jointly determined the temporal frequency. For instance, with 9 objects in the array, a speed of 1.1 rps would be 9.9 Hz. RESULTS. With only one target, tracking was not possible above about 9 Hz, far below the limits for perceiving the direction of the motion, and consistent with Verstraten, Cavanagh, & LaBianca (2000). The data additionally suggest a speed limit, with tracking impossible above 1.8 rps, even when temporal frequency was relatively low. Tracking two targets could only be done at lower speeds (1.4 rps) and lower temporal frequencies (6 Hz). This decrease is approximately that predicted if at high speeds and high temporal frequencies, only a single target could be tracked. Tracking three yielded still lower limits. Little impairment was seen at very slow speeds, suggesting these results were not caused by a reduction in spatial resolution. CONCLUSION. Splitting attention reduces the speed limits and the temporal frequency limits on tracking. We suggest a parallel processing resource is split among targets, with less resource on a target yielding poorer spatial and temporal precision and slower maximum speed.
Meeting abstract presented at VSS 2012