Characterizing Complexity: A Multidimensional Approach to Digital Control Room Display Research

Complexity can be characterized at numerous levels; physical, perceptual, and cognitive features all influence the overall complexity of an informational display. The Human Performance Test Facility (HPTF) at the U.S. Nuclear Regulatory Commission (NRC) develops lightweight simulator studies to examine the workload induced by various control room-related tasks in expert and non-expert populations. During the initial development of the lightweight simulator, cognitive complexity was defined based on the number of elements in each control panel. While the number of items roughly maps onto information density, it is only one of several features contributing to display complexity. This study is a follow-up to the original complexity evaluation and includes an initial characterization of the perceptual complexity of a set of control panels in their original (i.e., unmodified) and modified (for cognitive complexity reduction) forms. To assess perceptual complexity, a 3-dimensional approach was developed. The control panel displays were assessed using common measures of physical complexity (e.g., edge congestion, clutter, symmetry), performance-based measures (reaction time and accuracy for target identification), and subjective impressions using a survey adapted from a similar FAA assessment of air traffic controller workstation display complexity. Overall, the results suggested that clutter and symmetry were associated with target identification performance; participants interacting with high symmetry-low clutter displays identified target controls faster than those interacting with low symmetry-high clutter displays. Survey results tended to follow the same pattern as the physical and performance-based results; however, these patterns were not statistically significant, likely due to the small sample size. These initial results are a promising indication that the physical and performance-based measures were valid for assessing display complexity and that they are sensitive to differences in complexity, even with smaller samples. The physical and performance-based measures may be good candidates for human factors validation of future system designs - they are quick and easy to administer while providing a holistic sense of display perceptual complexity. Like other types of surveys, surveys for display complexity often require large samples to detect meaningful differences between groups. System designers and other stakeholders may want to consider alternative strategies, such as physical system measurement and characterization using performance-based methods if the user base is small or designs are in the early stages of development, requiring quick answers and an iterative approach to evaluation.