Tokyo Woman's Christian University, Zenpukuji 2-6-1, Suginami-ku, Tokyo 167-0041, Japan.
Tokyo Woman's Christian University, Zenpukuji 2-6-1, Suginami-ku, Tokyo 167-0041, Japan.
Vision Res. 2021 Aug;185:1-8. doi: 10.1016/j.visres.2021.03.006. Epub 2021 Apr 13.
Stroke width is an important factor affecting letter legibility. Although there seems to be a critical or optimal value for stroke width, it has been difficult to estimate quantitatively because shape deterioration and the increase of stroke width are covariates. This study attempted to predict the optimal value of stroke width considering it as a duty ratio. The duty ratio is related to the amplitude of the fundamental frequency, with the maximum amplitude of the fundamental frequency occurring at a duty ratio of 0.5. The fundamental frequency decreases when the duty ratio is set either lower or higher than 0.5. Based on previous research indicating that letters also have a critical band (CB), or the frequency band which contributes most to letter recognition, which corresponds to their fundamental frequency, we hypothesized that the amplitude of CB is related to the legibility of letters. We measured the contrast thresholds using square-wave gratings and letters of differing duty ratios. In both the grating and letter stimuli, the amplitude of CB reached its maximum when the duty ratio was around 0.5. Contrast thresholds for stimuli with various duty ratios were accurately predicted by the amplitudes of CB and the contrast thresholds in the individual's sine-wave grating. Our results suggest that the amplitude of a single critical component contributes significantly to the legibility of letters, even though they contain diverse frequency components.
笔画宽度是影响字母可辨认度的一个重要因素。虽然笔画宽度似乎存在一个临界值或最佳值，但由于形状劣化和笔画宽度的增加是协变量，因此很难进行定量估计。本研究试图将笔画宽度视为占空比来预测最佳值。占空比与基频的幅度有关，基频的最大幅度出现在占空比为 0.5 时。当占空比低于或高于 0.5 时，基频会降低。基于先前的研究表明，字母也有一个临界频带（CB），或者说是对字母识别贡献最大的频率带，与它们的基频相对应，我们假设 CB 的幅度与字母的可辨认度有关。我们使用方波光栅和不同占空比的字母来测量对比阈值。在光栅和字母刺激中，当占空比约为 0.5 时，CB 的幅度达到最大值。通过 CB 的幅度和个体正弦光栅的对比阈值，可以准确预测具有不同占空比的刺激的对比阈值。我们的结果表明，即使字母包含多种频率成分，单个临界成分的幅度对字母的可辨认度也有重要贡献。
