Fig. 5

NPD variation rate of individual subjects obtained by Eq. (1). P values are shown at the end of average bar by paired t test between each average of NPD variation rate of visual contact target material and average of NPD variation rate of 100%. And this paired t test results: *p < 0.05, **p < 0.01. Significant difference of 1% standard by paired t tests is recognized between average of wood panel and averages of both plastic panels, respectively. NPD near-point distance