Search time and subjective evaluation
Distraction increased search time. The result of matched samples t-test showed a significant difference (t=-6.721, p < 0.001) of subjects’ search time in non-distraction (M = 117.43, SD = 21.837) and distraction (M = 144.58, SD = 31.583). Meanwhile, the change of layout also increased the search time. The difference [F (2,70) = 11.045, p < 0.001, η2 = 0.240] of subjects' search time in horizontal (M = 102.86, SD = 34.42), vertical (M = 107.08, SD = 40.60) and square (M = 117.53, SD = 40.12) was also significant, which was tested by one-way repeated-measures ANOVA. The result was the same as we expected. Distraction and layout changed the difficulty, so the search efficiency was also different.
The difference (t=-22.405, p < 0.001) of the score of difficulty evaluation in distraction (M = 2.93, SD = 1.01) and distraction (M = 5.23, SD = 1.00) was significant. The results in horizontal (M = 3.00, SD = 1.01), vertical (M = 3.42, SD = 1.40) and square (M = 3.86, SD = 1.29) were also significantly different [F(1.418, 49.626) = 10.313, p = 0.001, η2 = 0.228]. The results showed that the participants' subjective evaluation of difficulty was consistent with the objective difficulty of the task, which was reflected in the search time.
When there were distractions in the page, fixation count, fixation duration and saccade count all increased (Fig. 6). The result of matched samples t-test showed that fixation count, fixation duration and saccade count all had significant effects (p < 0.05) in non-distraction and distraction. The change of layout also affected fixation count, fixation duration and saccade count. However, only fixation count had significant effects [F (2,70) = 23.556, P < 0.001, η2 = 0.402]. More specific trends are denoted by multiple comparisons of fixation count, fixation duration and saccade count, as shown in Fig. 7. The correlation analyses showed that fixation count, fixation duration and saccade count have significant effect (p < 0.05) on search time in non-distraction and distraction (Fig. 8) and in horizontal, vertical, and square (Fig. 9). All eye-tracking metrics were positively correlated with search time. The above results showed that the difficulty caused by the change of distraction and layout increased, making participants need more eye movement and more observing time.
The fixation points were connected by lines sequentially to obtain the trajectory of fixations which represents scan path. Both distraction and layout affected the trajectory of participants' fixation. Compared with non-distraction, distraction made participants' scan paths denser, but the random distribution of fixations did not change (Fig. 10). The difference of layout did not change the density of scan path, but the shape changed. Accumulated horizontal lines can be seen in horizontal, accumulated vertical lines can be seen in vertical, while there were more short lines in square (Fig. 11).
We have tried to create SAM (Scan -path Angle Mode) and apply it to the analysis. The proportional distribution of scan-path angle was a surprising discovery. The results of SA1P were very close in non-distraction (M = 32.72%, SD = 0.0208) and distraction (M = 31.66%, SD = 0.0503), and larger than SA2P, SA3P and SA4P, as shown in Fig. 12. This trend was more obvious in layout group, in which the results of SA1P in horizontal (M = 45.00%, SD = 0.0535), vertical (M = 41.05%, SD = 0.0499) and square (M = 44.39%, SD = 0.0402) were shown in Fig. 13. When distraction added, the results of SA2P, SA3P and SA4P were very similar in non-distraction and distraction. However, after the layout changed, the results of SA2P, SA3P and SA4P were different in horizontal, vertical, and square.