Evolved navigation theory and the environmental vertical illusion
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These studies suggested that everyday visual perception is unconsciously subject to large-scale illusions on ubiquitous environmental surfaces. Participants overestimated environmentally vertical surfaces and did so to an increasing degree with longer surfaces, neither of which occurred with environmentally horizontal surfaces. I title this illusion the environmental vertical illusion. The severity of previous injury from a fall related to the degree of illusion such that more severe previous falling injuries were associated with lower illusion magnitudes, even though the illusion is still present at higher injury severities. I predicted these data from hypotheses derived from Evolved Navigation Theory (ENT), which focuses on how navigational costs over evolutionary time can shape cognitive and perceptual mechanisms. Virtual reality data suggested that unrealistically artificial falling costs failed to produce the environmental vertical illusion, even on apparently vertical surfaces. Virtual reality methods also suggested that distance estimation from immobile visual displays deviated from natural distance estimation in important ways that hold implications for tasks involved in piloting and surgery. Data from physical and virtual reality suggested that no clear relationship existed between the 2D Vertical-Horizontal Illusion and 3D distance estimates gathered here. The current findings hold implications outlined under ENT for areas such as anxiety disorders, piloting, surgery, individual differences, and visual stimuli design. However, these findings may be most important because distance and orientation perception occurs constantly in most visual systems and, consequently, most behaviors. Understanding how distance perception occurs thus helps us to understand one of the most common of all psychological experiences. These data suggest that a primary component of human visual experience is illusory. However, through the use of a theory rooted in evolution (ENT), we may be able to predict and better understand these important features of human psychology.