A goal of human-robot interaction is to allow one user to operate multiple robots simultaneously. In such a scenario the robots provide leverage to the user's attention. The number of such robots that can be operated is called the fan-out of a human-robot team. Robots that have high neglect tolerance and lower interaction time will achieve higher fan-out. We define an equation that relates fan-out to a robot's activity time and its interaction time. We describe how to measure activity time and fan-out. We then use the fan-out equation to compute interaction effort. We can use this interaction effort as a measure of the effectiveness of a human-robot interaction design. We describe experiments that validate the fan-out equation and its use as a metric for improving human-robot interaction.

A goal of human-robot interaction is to expand the capability of human beings so that they can control multiple robots simultaneously. This provides leverage for human attention beyond single robot interaction. The number of such robots that can be operated is called the fan-out of a human-robot team. We define the concepts of neglect-tolerance as a measure of autonomy and interaction-effort as a measure of required human attention. A model for fan-out is presented that predicts a human's ability to control multiple robots. We validate this model using robot simulations and user studies. Using the validated model we demonstrate enhanced task performance on physical robots as predicted by the model.