Tactile Elevation Perception in Blind and Sighted Participants and Its Implications for Tactile Map Creation

Objective: Our goal was to determine the optimal elevation of tactile map symbols. Background: Tactile perception research predicts that symbol elevation (vertical height) and texture on tactile maps could influence their readability. However, although research has shown that elevation influences detection and discrimination thresholds for single tactile stimuli and that the physiological response of fingertip receptors varies with texture, little is known about the influence of these parameters on the identification of stimuli in the context of multiple symbols as found on tactile maps. Method: Sighted and visually impaired participants performed tactile symbol identification tasks. In Experiment 1, we measured the effect of elevation on identification accuracy. In Experiment 2, we measured the effect of elevation and symbol texture on identification speed. Results: Symbol elevation influenced both speed and accuracy of identification; thresholds were higher than those found in work on detection and discrimination but lower than on existing tactile maps. Furthermore, as predicted from existing knowledge of tactile perception, rough features were identified more quickly than smooth ones. Finally, visually impaired participants performed better than sighted ones. Conclusion: The symbol elevations necessary for identification (0.040 to 0.080 mm) are considerably lower than would be expected on the basis of existing tactile maps (generally 0.5 mm or higher) and design guidelines (0.4 mm). Application: Tactile map production costs could be reduced and map durability increased by reducing symbol elevation. Furthermore, legibility of maps could be improved by using rough features, which are read more easily, and smaller symbols, which reduce crowding of graphics.