Interactions between memory scanning and visual scanning in display monitoring

Many real-world tasks require the simultaneous performance of memory scanning of several memorized items and visual scanning of several physically separated sources of information in the visual field. This paper reports a study that was conducted to quantify the possible interactions between memory scanning and visual scanning. A quantitative model was derived to integrate Sternberg's linear model of memory scanning and Neisser's linear model of visual scanning. The derived model was tested through two experiments. The experiments simulated a process controller's task of monitoring an array of instrument meters to detect if any of them indicated a system error. The subjects were required to keep a number of items in their working memory (the definition of errors) and search through an organized array of instrument meters to decide whether any of the meters carried an item that matched any of the memorized items in their working memory. Two experimental factors were investigated in both experiments: the number of memorized items and the number of circles needed to be searched. These defined memory scanning demand and visual scanning demand respectively. Experiment 1 employed a different set of memorized items for each experimental trial, whereas experiment 2 employed the same set for all the trials that had the same experimental condition. The experiments identified both the strengths and the limitations of the derived model. Implications for human-machine interface design and human performance modelling are discussed.