The effect of the Muller-Lyer illusion on map reading

One important reason for studying visual illusions is that they can influence real-world perception as people interact with human-made displays. Three experiments examined how the Muller-Lyer illusion affects distance judgments and decision-making in the complex graphical context of a map by having subjects estimate the lengths of road segment lines framed by inward-going or outward-going wings in actual maps, in control displays that had the map context removed, and in simulated maps. The experiments showed that (1) outward-going wings led to higher distance estimates than did inward-going wings to the same extent both with and without the map context, (2) decisions based on distances determined from maps were affected by Muller-Lyer elements in the maps, and (3) map readers' measurement behavior influenced the effect of the Muller-Lyer elements in maps. The discussion focuses on how certain display manipulations and task manipulations affect the Muller-Lyer illusion. In addition, the discussion addresses the instances in which using a map might be affected by misestimation due to Muller-Lyer elements.