*3.2. Identification Tests*

As the subjects were given a random color sample, they were asked to identify the color and its tone corresponding to the cross-modular tactile pattern of ColorWatch. Time slots of fifteen minutes each for both the learning phase and color identification tests were allocated per subject, based on preliminary evaluation and improvisations from our group. To avoid prejudices from previous tests, and to make participants feel comfortable in their subjective identifications; the subjects were informed of flexible time limits. However, all the subjects completed the learning phase and identification tests within fifteen minutes for each stage. The square and the round disk could be easily distinguished from each other, in addition to the tactile embodiment on them since they are placed at distinct positions intersecting traditional clock hands. The six color-hues are located such as the complementary colors are on opposite ends from each other. Hence, it all came down for subjects to remember only three colors with their respective positioning on ColorWatch, and understanding the key idea for monochromatic and achromatic colors, and their tones. The subjects were quick to learn the pattern and reported no trouble in getting familiarized with the ColorWatch idea and its large scale prototype. During color identification tests on fifteen subjects, no feedback for their identifications was provided to them during tests, and no color sample or their identification was repeated for any case. All the identifications made were correct as shown in Table 3, except a total of three wrong identifications. The subject 'S2' misidentified light versus dark yellow and subject 'S13' misidentified a color tone for achromatic color, yielding the total correct identification rate at 99.17%.


**Table 3.** The correct identifications out of total color identifications made by fifteen subjects for ColorWatch color gamut.

### *3.3. Workload Assessment*

The NASA Task Load Index (NASA-TLX) is considered the gold standard for subjective workload measurement. It was developed by the Human Performance Group at NASA's Ames Research Center and can evaluate task demands and workload of an individual performing it based on task, behavior, and subject-related scales [34]. The task-related scales are used to measure the objective demands of the task, the behavior-related scale reflects upon an individual's subjective evaluation of the task, while the subject related scale accounts for the psychological impact on the individual. The NASA-TLX test can be applied to evaluate quantitative subjective mental workload assessment of a service, system, or task based on six indicators. The indicators and evaluated scores for subjects are shown in Table 4. The scale from 1 to 10 points is chosen for the ease and familiarity of participants, with 1 ranging from very low to 10 being very high. Typically, the measured scores for different indicators are assigned weights corresponding to their relative importance, but some studies such as [35] have used raw TLX tests. Considering the subjective

nature of the task in this study, we have evaluated the raw TLX test using uniform weights for all indicators.


**Table 4.** NASA-TLX test questions with subject wise score selection.

Figure 6 summarizes workload assessment scores for subjects under the NASA-TLX test. The indicators for mental, physical, and temporal demands, effort, and frustration all score less than the median value for the scoring range of 1–10. Most of the participants were very quick to learn the tactile interface for color translation and they requested to start the tests without consuming most of the learning phase time of fifteen minutes given to them. Given that the physical and temporal demands are very low for the proposed system, the mental demand and efforts put on by the users may vary from person to person, as it has been reflected by their respective standard deviations. The mean scores for both mental demand and effort lie in the medium-low of scoring range for the test, and less than the median for scoring range. However, few subjects suggested that it might be easier with more practice. The proposed system is promising in terms of user satisfaction as the performance indicator for user satisfaction scored highest while the frustration indicator scored lowest among all the indicators for this test.

**Figure 6.** Workload assessment scores for NASA-TLX test question indicators.
