Chapter 3. Effects of Display Curvature, Display Zone, and Task Duration
3.3. Results
Cronbach’s α between the ECQ items was 0.85 (pre) and 0.83 (post), indicating internal consistency (Gouttebarge et al., 2004; Steenstra et al., 2009). The ICC values for the initial ECQ scores and CFF values (i.e., before the visual tasks) were 0.89 and 0.93, indicating that the participants were homogeneous (Gouttebarge et al., 2004; Steenstra et al., 2009) in terms of their initial ECQ scores and CFF values. The results of the two ANOVA tests, i.e., ANOVA for display curvature, display zone, and task duration and ANOVA for display curvature and visual tasking, are presented in table 3.2.
Table 3.2 p-values for effects of display curvature (DC), display zone (DZ), task duration (TD), and visual tasking (VT) on legibility and visual fatigue (p-values less than 0.05 are underlined)
Effects
Legibility Visual Fatigue
Letter Searching
Error
Letter Searching
Speed
Subjective (VAS)
Subjective (ECQ)
Physiological (CFF)
Display Curvature (DC) .022 .0001 .039 .61 .32
Display Zone (DZ) .028 <.0001 <.0001
Task Duration (TD) .080 .063 <.0001
DC × DZ .021 <.0001 .009
DC × TD .70 .13 .35
DZ × TD .49 .073 .58
DC × DZ × TD .55 .59 .60
Visual tasking
(VT) <.0001 .02DC × VT .28 .27
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3.3.1. Visual searching task performance 3.3.1.1. Letter searching error
For the letter searching error (%), the interaction effect of the display curvature × display zone was significant (Table 3.2 and Figure 3.5). The leftmost display zone (Z1) of the flat display setting showed the highest letter searching error and was grouped differently from all the other settings, except for the rightmost ones (Z5) of the 400 R and flat settings. The effect of display curvature was significant. The 1200 R curvature setting was grouped differently from the flat setting, with a mean (SD) letter searching error of 9.8 (7.0) for the former vs. 12.2 (9.8) for the latter. The effect of display zone was also significant, and Z1 and Z3 were grouped differently, with a mean (SD) letter searching error of 11.7 (9.1) for Z1 vs. 9.9 (6.9) for Z3. Three contrasts (C1, C3, and C4) were significant (p ≤ .03), with the mean letter searching error of (Z1+Z5)/2 being higher than those of (Z2+Z4)/2 and Z3, and the mean letter searching error of (Z1+Z2+Z4+Z5)/4 being higher than that of Z3. Further, the mean (SD) letter searching error was 9.9 (6.9), 10.4 (6.5), 11.5 (7.6), and 10.9 (6.5) for Z3, (Z2+Z4)/2, (Z1+Z5)/2, and (Z1+ Z2+Z4+Z5)/4, respectively.
Figure 3.5 Effects of display curvature and display zone on letter searching error (Z denotes display zone, where Z1 is the leftmost zone, Z3 is the center zone, and Z5 is the rightmost zone;
Tukey’s HSD grouping is indicated in parentheses; SD range: 4.7–10.1)
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3.3.1.2. Letter searching speed
For the letter searching speed (letters/s), the interaction effect of display curvature × display zone was significant (Table 3.2 and Figure 3.6). Z1 in the flat setting showed the lowest speed, and Z1
and Z5 in the flat setting were grouped differently from all the other settings. The effect of display curvature was significant with the 400 R and 600 R settings grouped differently from the other settings. The mean (SD) letter searching speed was 12.6 (2.6), 12.6 (2.4), 12.0 (2.5), and 11.8 (2.9) for the 400 R, 600 R, 1200 R, and flat settings, respectively. The effect of display zone was significant. Z1 and Z5 were grouped differently from Z2 and Z3, with the mean (SD) letter searching speed being 11.9 (2.6), 12.0 (2.7), 12.4 (2.6), and 12.6 (2.7) for Z1, Z5, Z2, and Z3, respectively. Three contrasts (C1, C3, and C4) were significant (p < .0001), with the mean letter searching speeds of Z3, (Z2+Z4)/2, and Z3 being higher than those of (Z1+Z5)/2, (Z1+Z5)/2, and (Z1+Z2+Z4+Z5)/4, respectively. Further, the mean (SD) letter searching speed was 12.6 (2.7), 12.4 (2.5), 12.0 (2.5), and 12.2 (2.4) for Z3, (Z2+Z4)/2, (Z1+Z5)/2, and (Z1+Z2+Z4+Z5)/4, respectively.
Figure 3.6 Effects of display curvature and display zone on letter searching speed (Z denotes display zone, where Z1 is the leftmost zone, Z3 is the center zone, and Z5 is the rightmost zone;
Tukey’s HSD grouping is indicated in parentheses; SD range: 2.1–3.0)
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3.3.2. Visual fatigue
3.3.2.1. Subjective visual fatigue (VAS)
For the visual fatigue reported on the VAS, the interaction effect of display curvature × display zone was significant (Table 3.2 and Figure 3.7). Z1 in the flat setting showed the highest visual fatigue and was grouped differently from the other settings except for Z5 in the flat setting. The effect of display curvature was significant. The 600 R and flat settings were grouped differently, with a mean (SD) VAS score of 42.6 (22.6) for the former vs. 49.1 (24.0) for the latter. The effect of display zone was also significant. Z3 was grouped differently from Z1 and Z5, with a mean (SD) VAS score of 40.6 (23.9), 50.0 (23.4), and 47.0 (21.6) for Z3, Z1, and Z5, respectively.
All four contrasts (C1, C2, C3, and C4) were significant (p ≤ .009), with the mean VAS scores of (Z1+Z5)/2, (Z2+Z4)/2, (Z1+Z5)/2, and (Z1+Z2+Z4+Z5)/4 being higher than those of Z3, Z3, (Z2+Z4)/2, and Z3, respectively. Further, the mean (SD) VAS score was 40.6 (23.9), 44.0 (21.8), 48.5 (21.2), and 46.2 (20.6) for Z3, (Z2+Z4)/2, (Z1+Z5)/2, and (Z1+Z2+Z4+Z5)/4, respectively. The effect of task duration was significant, with the mean (SD) VAS score being 40.7 (21.6) for the first set vs.
49.5 (23.9) for the second set.
Figure 3.7 Effects of display curvature and display zone on subjective visual fatigue after two sets of visual tasks (0 – no visual fatigue, 100 – very severe visual fatigue) (Z denotes display zone, where Z1 is the leftmost zone, Z3 is the centre zone, and Z5 is the rightmost zone; Tukey’s
HSD grouping is indicated in parentheses; SD range: 2.1–3.0)
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3.3.2.2. Subjective (ECQ) and psychophysiological (CFF) visual fatigue
Based on the ECQ scores measured before and after the two sets of five visual search tasks in each curvature setting, the effect of visual tasking was significant, with the mean (SD) ECQ score increasing from 11.6 (9.4) to 23.4 (12.2) (Table 3.2 and Figure 3.8). Similarly, based on the CFF values, the effect of visual tasking was significant, with the mean (SD) CFF value decreasing from 41.6 (1.4) to 41.3 (1.4) (Figure 3.8).
Figure 3.8