Kaber DB, Alexander AL, Stelzer EM, Kim S-H, Kaufmann K, Hsiang S. Perceived clutter in advanced cockpit displays: measurement and modeling with experienced pilots. Aviat Space Environ Med 2008; 79:1007–18. Introduction: Synthetic and enhanced vision systems (SVS and EVS) are being introduced into the cockpit to promote safety under workload conditions. Integration of existing iconic imagery with SVS and EVS displays may lead to perceptions of clutter. This research evaluated head-up display (HUD) features, including SVS, EVS, traffic collision avoidance system symbology, flight pathway (TUNNEL) guidance, and different primary flight display symbol sets, on pilot perceptions of clutter. A perceptual decomposition of the construct of clutter was also conducted. Method: During a simulated landing, 4 expert pilots viewed images of 16 HUD configurations. Pilots rated clutter for each image and the utility of pairs of terms for describing clutter. Results: Results revealed all HUD features and two-way interactions to be significant in perceived clutter. Ratings increased with additional features. The presence of EVS, TUNNEL, and an expanded symbol set contributed the most. Regression models were developed to predict the likelihood of clutter ratings based on pilot perceptions of display characteristics. Pairs of terms found to have the greatest use for describing clutter included “redundant/orthogonal,” “monochromatic/colorful,” “salient/not salient,” “safe/unsafe,” and “dense/sparse” (in that order). A factor analysis revealed underlying display qualities explaining ∼78% of variability in perceived clutter, including global density, feature similarity, feature clarity, and the dynamic nature of displays. These qualities corresponded with the display descriptor terms plus the terms “static/dynamic.” Discussion: The study provided information on the relationship of display features and pilot perceptions of clutter. We identified terminology pilots use to describe clutter and latent display variables that drive perceived clutter.