Dividing attention between the color and the shape of objects.

In many dual-task experiments, the priority observers give to each task is experimentally varied. Most experiments using this methodology have studied the effect of dividing attention between spatially distinct objects. We examined performance when attention had to be divided between stimulus attributes other than spatial location. In the first experiment, observers identified the color and the shape of a single letter. Accuracy was the same for single- and dual-task conditions, and a trial-by-trial analysis revealed a strong positive correlation in the correct identification of the color and the shape. In the second experiment, color and shape judgments were separated in space, with opposite results: Dual-task performance was worse than single-task performance, and the trial-by-trial analysis indicated a strong negative correlation between tasks. The results indicated that often only one dimension was processed within a trial. The results support object and space models of attention.