Mixed-initiative Multirobot Control in USAR

Abstract

In this experiment, the first of a series investigating control of cooperating teams of robots, cooperation was limited to deconfliction of plans so that robots did not re-explore the same regions or interfere with one another. The experiment found that even this limited degree of autonomous cooperation helped in the control of multiple robots. The results showed that cooperative autonomy among robots helped the operators explore more areas and find more victims. The fully autonomous control condition demonstrates that this improvement was not due solely to autonomous task performance as found in (Schurr et al. 2005) but rather resulted from mixed initiative cooperation with the robotic team. The superiority of mixed initiative control was far from a foregone conclusion since earlier studies with comparable numbers of individually autonomous robots (Trouvain & Wolf 2002; Nielsen et al. 2003; Trouvain et al. 2003; Crandall et al. 2005) found poorer performance for higher levels of autonomy at similar tasks. We believe that differences between navigation and search tasks may help explain these results. In navigation, moment to moment control must reside with either the robot or the human. When control is ceded to the robot the human’s workload is reduced but task performance declines due to loss of human perceptual and decision making capabilities. Search by contrast can be partitioned into navigation and perceptual subtasks allowing the human and robot to share task responsibilities improving performance. This explanation suggests that increases in task complexity should widen the performance gap between cooperative and individually autonomous systems. We did not collect workload measures to check for the decreases found to accompany increased autonomy in earlier studies (Trouvain & Wolf 2002; Nielsen et al. 2003; Trouvain et al. 2003; Crandall et al. 2005), however, eleven of our fourteen subjects reported benefiting from robot cooperation. Our most interesting finding involved the relation between performance and switching of attention among the robots. In both the manual and mixed initiative conditions participants divided their attention approximately equally among the robots but in the mixed initiative mode they switched among robots more rapidly. Psychologists (Meiran et al. 2000) have found task switching to impose cognitive costs and switching costs have previously been reported (Squire et al. 2003; Goodrich et al. 2005) for multi-robot control. Higher switching costs might be expected to degrade performance, however in this study; more rapid switching was associated with improved performance in both manual and mixed initiative conditions. We believe that the map component at the bottom of the display helped mitigate