Size Discriminability of Circular Tactile Point Symbols

－Comparison between Blind and Sighted People－

Abstract

To find highly discriminable combinations of circular tactile point symbols on swell paper, we presented pairs of tactile circular point symbols with diameters varying between 1.0 mm and 5.0 mm in 0.5 mm steps to 12 blind and 12 sighted participants in a paired comparison experiment. The participants were asked which dot was larger or if both were the same size. The difference thresholds for the size of the circles increased as the diameter of the reference stimulus increased. They were found to range from 0.5 mm to 0.7 mm. These values are lower than the values obtained in previous research. Possible reasons for this difference were the difference in diameter steps and the removal of the data of the participants with great ambiguity. A two-way ANOVA test between the participant groups did not show a significant main effect; the blind participants did not surpass the sighted in terms of the difference threshold. The threshold values obtained in this experiment were utilized in the design of a tactile star wheel for the blind.