**4. Discussion**

According to the National Federation of the Blind, braille literacy has been on the decline. Out of 1.3 million legally blind people in the USA, only 10% of them can read braille. Moreover, only 10% or blind children are learning braille, calling it "The Braille literacy crisis in America", which limits the prospects of braille based designs [39]. The braille watches [22–24] can theoretically be used as a digital braille interface if combined with color sensing and color recognition systems; however, no such scheme has been presented by the developers. A summary and comparison of these have been provided in Table 6. Analog time watches with conventional rotating hands exhibit gradually altering angular orientation because the hands move continuously with passing time, whereas digital time watches numerically convey time. The continuously rotating analog watch hands provide a means to the human brain for instantaneous spatial recognition, such as the relative difference between two time-stamps and the apprehension of remaining time until an event. Situations like these for an analog watch do not strictly engage mental numeric calculations, which is conversely true for a digital watch where brief mental calculations are required for interpreting these events. In terms of human perception, it is a matter of spatial recognition versus mental numeric calculations. Likewise, a mere description of color in text or braille manner in a theoretical scenario of inclusion of color information through braille watch might not be sufficient for PVI perception as it lacks the essence of color nature, their relative relationships, and interpretation.

Related works are focused on the tactile translation of colors in artworks, which limits the usability of those schemes in daily life. They also have high learnability requirements, and cannot be used for the color perception of arbitrary objects. We have integrated perceptual color patterns with analog watch design in an intuitive arrangement. The subjects' feedback validated the effectiveness of ColorWatch TCP as there were only a few incorrect color identifications, and almost all of the identifications were correct. The subjects were also able to understand the tactile-color association and the way they are organized on the watch design. It enabled them to quickly recall the correct related color for the detected angular position on the disk. The subjects reported the ease of tactile dot detection on the square disk in comparison with the round disk. This might be caused by a fewer number of probable positions for the tactile dot on the square disk rather than the round disk. Another possible reason for that may be the shape of the square disk which conserves its apparent tactile shape perception even after rotations at 90°, and the angular position of the tactile dot at one corner of it can be identified relative to its distinct and conserved geometry. A similar effect can be achieved for one tactile dot detection of any regular polygon shape, if the number of distinct positions or the number of fixed angle rotations it takes for one full revolution is a factor of the number of polygon vertices. The reason for the round shape of the larger disk for color hue in color perception, and the minute pointer in timepiece mode is chosen instead of a polygon shape is to help identify continuous rotations for the minute pointer in timepiece mode. Moreover, the continuous movement of round disk or minute hand can provide more precise time, instead of fixed rotations for every five minutes, for example. The color gamu<sup>t</sup> of ColorWatch might be

further extended to represent eight color hues, each for three levels of color tones along with eight levels of achromatic colors as shown in Figure 1e. In this way, the colors are placed at 60°angles on the color wheel, capable of presenting 32 colors. The dynamic nature of spatial color recognition for reference color and easy learnability makes it particular among TCPs from relevant research. A brief comparison for relevant works is provided in Table 7. This might help PVIs as an assistive device as the overall rating of 'Good' is reflected by test subjects' responses. The workload assessment test also validates it to be suitable for a broad population of potential PVI users with low learnability requirements, as indicated by below-average scores of mental demand coupled with low frustration, and higher satisfaction about performing the task correctly.

### **Table 6.** Features and comparison of tactile watches.


**Table 7.** The overview and comparison with relevant works on tactile color pictograms.


The contributions of this study are listed here:

