Illusions in reading maps by touch: reducing distance errors

The study reports systematic distance errors in reading raised-line maps by touch, and how they can be reduced. We show that T-shaped road junctions produce the typical error due to overestimating the length of the bisecting road compared to the bisected road. The error was not reduced when the target location was marked initially by a symbol. However, it was eliminated by instructions to use both hands concurrently to scan the route relative to an external square frame surrounding the map layout and to the body midline. Road junctions, which resemble 'Müller-Lyer' configurations, produced a significant overestimation of the length of a road that ended in diverging side roads relative to underestimating a road section with converging side roads. Spatial anchor cues from landmarks along the route, either alone or in conjunction with the spatial frame instructions, eliminated the illusion equally. We discuss theoretical implications, and the use of map frames and landmarks as spatial guides to improve map use by touch.