Divided attention can be deadly, as we know from warnings not to text or talk while driving. But why exactly is it sometimes difficult to divide our attention between two tasks like driving and talking? Back in the 1980’s, psychologists were testing and debating several competing theories to explain the costs of doing two things at once. Chris Wickens and I wondered if perhaps some of these different theories were not really competing after all but were rather complementary, each tapping into different ways that simultaneous tasks might interfere with each other. Could we design an experiment that would help us find out?
We realized that a dual-axis tracking task could provide us with the opportunity to test the distinctive contributions of different sources of difficulty in divided attention. Dual-axis tracking, after all, could be configured in different ways such that, on one hand, subjects were literally performing two separate one-dimensional tracking tasks simultaneously or, on the other hand, performing a single tracking task in two dimensions. We knew that control system engineers had devised mathematically sophisticated ways of measuring tracking performance that might reveal more precisely what the sources of interference in dual-axis tracking could be. So we designed an experiment in which we measured how well participants performed dual-axis tracking tasks under a variety of different configurations, and then we looked at what our results meant for the different competing or complementary theories in play.
Abstract
Why do people often find that performing two tasks at once is harder than performing one task at a time? Three mechanisms of task interference that might answer that question were investigated: resource competition, confusions, and incompatible task proximity between processing stages. The subjects performed dual-axis compensatory tracking with error displays that were either integrated or separated, with axis controls that either were integrated into one stick or remained separate, and with control dynamics on the two axes that were either the same or different. Tracking error increased and control activity decreased as a function of the combined difficulty of the two control dynamics. Integrated displays and integrated controls both led to increased confusions between tracking axes although error was not reliably affected. Significantly, performance was also affected by whether the integrality of displays matched that of controls. These results suggest that resource competition, confusions, and compatibility of proximity play distinct roles in dual-axis tracking performance.
Citation
Fracker, M. L., & Wickens, C. D. (1989). Resources, confusions, and compatibility in dual-axis tracking: Displays, controls, and dynamics. Journal of Experimental Psychology: Human Perception and Performance, 15(1), 80–96.
Dr Martin Fracker 