Tactile Detection by Blind People of Embossed Lines and Squares with Selected Dot Elevation

Dot elevation and dot density are two main variables that dominate the recognition and conceptualization of tactile embossed graphics by blind individuals. Nevertheless, few studies have investigated tactile sensitivity to the elevation (third dimension) of tactile graphics. In a pilot experiment we conducted recently using 8 dot elevations of embossed lines and squares, in 20 or 10 dpi, produced by a Tiger VP200 braille embosser, we observed that participants can detect only two highs with accuracy above 50%. We present here the results of an experimental study with 30 congenitally blind participants to investigate the detection accuracy of embossed tactile lines and squares in four selected dot elevations among the eight possible dot heights that can be produced by the VP200 embosser. A total of 1,920 responses were recorded. 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 for the raised-dot lines and squares stimuli. Moreover, the overall mean response time of the detection task is provided. We observed that in all cases, only the stimuli with the lower two heights H-1 and H-3 provide detection accuracy above 70%.