Communications of the ACM

compared to the dashboard with no overuse of colors. However, this excess effort did not affect performance of the task. The sample heat map of two subjects (see Figure 3) reflects the presence of cognitive overload. A heat map uses different colors—red for the largest number of fixations, green for the fewest number of fixations—to show the number of fixations viewers make in certain areas of an image. 6 The heat map on the left of the figure indicates the subject spent significant time on all bars with different colors. In contrast, the heat map on the right of the figure shows how another subject spent time on specific bars.

Analysis of Misuse of Colors

Task performance between the two groups sho wed no statistical difference. Approximately 88% of the subjects (or 26 of the 30) answered the task correctly in both groups. However, a significant difference was found in the overall fixation durations and counts between the two groups. To perform the task, subjects who viewed the dashboard with misuse of colors took approximately 45 seconds, whereas those who viewed the dashboard with no such misuse took approximately 27 seconds; Table 2 shows the results of the independent sample t test, indicating a high cognitive load exists for viewers of the dashboard with misuse of colors.

To determine whether there was a System 1, then System 2 sequence, the study identified task-relevant and task-non-relevant areas. First, a specific task non-relevant area was identified from the dashboard that did not have to be viewed to perform the task. This area is the bar that indicates the small market in the East zone (dark red) for the chart “market type by market size” that appears in the top part of the lower panel of Figure 2. The time of the first fixation was obtained when a viewer would look at this dark red bar. This time was compared with the first fixation time of the same area (light blue) in the top part of the top panel in Figure 2. On average, the subjects using the dashboard with misuse of colors looked at this area within 6. 2 seconds of their average viewing time of 45. 2 seconds. On the other hand, subjects using the dashboard with no such misuse looked at this specific area within 18. 2 seconds of their average viewing time of 26. 8 section time on task-relevant areas.

The identification of a System 1, then System 2 activation sequence is easier for dashboards that misuse colors because viewers readily recognize the task-relevant and task non-relevant areas, as in Figure 2. This sequence identification is not possible for dashboards that overuse colors because the areas overlap, as in Figure 1.

This study followed a design in which subjects were randomly assigned to one of the variations—overuse vs. no overuse of colors and misuse vs. no misuse of colors—in dashboards. Each group included an equal number of subjects. One variation was provided to 15 subjects, and the other to the rest. The order of the dashboards was randomized; that is, some subjects received dashboards with or without overuse of colors first and some received dashboards with or without misuse of colors first. The subjects performed two tasks related to the two dashboards as their eye movements were tracked. Prior to tracking, subjects’ eyes were calibrated and validated. Following calibration, the subjects were shown a task on a screen and asked to read it carefully. They then saw the dashboard and verbalized an answer. This sequence was used to avoid eye movements associated with writing down answers. The sequence was repeated for each dashboard and eye movements were tracked through EyeLink 1000 software. Verbalizations were also recorded. The tracker recorded a minimum fixation time of four milliseconds.

Analysis of Overuse of Colors

The accuracy of the analysis between the two groups showed no statistical difference. Nearly 92% of the subjects (or 28 of the 30) answered the task correctly in both groups. But total fixation duration and fixation counts for the tasks were compared between the two groups, finding significant differences. Subjects who used the dashboard with overuse of colors took approximately 28 seconds, while those who viewed the dashboard with no such misuse took approximately 22 seconds. The independent sample t test (see Table 1) confirmed the differences in fixation durations; counts were significant in the two groups.