The legibility of a letter may be influenced by a lot of factors, in which both structural characteristics of a letter and psychological factors would be involved. Many relevant researches have been reported so far, but they could not afford evidence as to how those factors determine the legibility and also what quantitative combinations of those factors have a share in the legibility. The purpose of this paper is to clarify these points by the employment of a multiple regression method.
The quantized 46 Kata-Kana letters contaminated by visual noise (Fig. 1), for which 4 noise levels, labelled as
P6,
P9,
P135, and
P203, were prepared, were used to give an index of the legibility of a letter (Table 3). The obtained legibility was intended to be explained by 9 factors, which were named as the internal redundancy (Factors 1 to 4), the component of direction (Factors 5 to 8), and the frequency (Factor 9).
The multiple regression analysis done at 4 noise levels provided us with standard regression coefficients and regression correlation coefficients of 9 predictor variables (Table 8), which revealed relative importance of factors determining the legibility, and also multiple correlation coefficients
R (Table 8), showing an over-all aspect of discrepancies between the actual proportion of correct identification and the one estimated by the equation (4). The following results were obtained.
1. The highest multiple correlation coefficient was shown at the
P135 noise level, i.e., when noise cells are contained in a mesh with the probability 0.135.
2. The longitudinally-scanned redundancy (factor 2), the left-directionallyscanned redundancy (factor 4), the component of horizontal direction (factor 5), and the component of longitudinal direction (factor 6) were identified as positive factors participating in the legibility.
3. The right-directionally-scanned redundancy (factor 3) and the component of right direction (factor 8) were regarded as trivial factors.
4. The factor of frequency (factor 9), which was a sole psychological factor, among the analyzed variables, negatively affected the legibility through all of the noise levels.
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