Ecological warnings

• Understanding the evolutionary “meaning” of stimuli can lead to better warning stimuli.
• Face stimuli–both muscular expressions and color signals–are a rich, universal source.
• Cultural selection may have already selected for warning-related symbols to have angry-face stimulus features.
• Classical geometrical illusions, and variants on them, can be designed to better attract the attention of viewers.
• Static warning stimuli can be designed so that they perceptually dynamically change as needed.

Our visual system has evolved over hundreds of millions of years, and is finely honed for processing natural scenes. It is reasonable to expect that warning signs that can more closely mimic ancestrally alerting stimuli (or “supernormal” versions of such stimuli) in nature would be among the most effective even today. Here we investigate warning symbols from an ecological standpoint, specifically in light of recent research in three areas of vision: color perception, the evolution of writing and typography, and visual illusions. We discuss how the color and geometry of an angry face, for example, may underly the superiority of red color and V shapes in warnings. We also describe simple heuristic ecology-based rules for the design of text in warning signs. Finally, we take up how radial line stimuli and the illusory effects they induce can be harnessed for capturing the attention of an observer, orienting him toward a warning symbol, and deterring him from moving closer.