Tactile identification of embossed lines and square areas in diverse dot heights by blind individuals

Most of the braille embossers incorporate a mode for the creation of braille embossed graphics (BEG). Some of them can produce dots in different elevations, but also various dot densities. Dot elevation and dot density constitute the main variables that dominate the identification and conceptualization by blind users of tactile elements, such as lines and areas, in BEG. Nevertheless, there are not enough published research data in this domain. We present the results of a study with 30 congenitally blind participants to examine their detection performance in tactile identification of context-free embossed lines and square areas in eight dot elevations H1 to H8 (from 0.03 to 0.47 mm) and two dot densities (10 and 20 dpi). The detection accuracy and response time of the matching task were examined for each type of test stimuli. The results of correct and misclassified stimuli are presented in confusion matrixes, along with the overall mean response time for each task. The participants classify with better accuracy the stimuli with the three lower dot elevations (between 0.03 mm and 0.15 mm) for both types of stimuli and in both dot densities. The minimum overall mean response time of the identification task was achieved for the larger dot height H8 in the case of raised-dot square areas of 10 dpi. The analysis of the results indicates that better classification accuracy is achieved with the combination of four dot heights H1, H2, H4, and H8. Blind users can distinguish textures produced by dots with very low heights in line with the recent literature suggestions. The current study constitutes a first step toward recommendations for the designers of BEG in applying textures with variable dot height and dot density for educational purposes or for producing tactile maps to benefit users who are blind.