Comparison of VAS and Direct Numerical Evaluation in Visual Sensitivity Testing of Grayscale Images

Abstract

Our goal is to quantify the subtle differences in individual perceptions, and we explore the possibility of the VAS being able to represent indices other than pain. We consider that VAS's advantage should be contrasted with the Likert Scale and that the advantage of VAS is that it can be expressed in detail as a point on a linear number line, not as a stepped expression. We studied it was necessary to investigate the performance of the VAS. In this study, we compared the method of expressing subjectivity on a number line to express subjectivity directly on a number line, such as the NRS. However, we did not use the NRS, which expresses subjectivity on a scale of 11, as it is, but adopted a method of expressing subjectivity directly as a numerical value. For example, in the VAS, the distance between the straight line of 100 mm and the mark's left side is used as the measurement value. We convert this measurement into the value of the interval [0, 1] and use it. Therefore, we refer to the evaluation by the value of the interval [0, 1] as the Ex-NRS, which is directly inputted instead of the NRS that evaluates in 11 steps. In this paper, we report a comparison between a numerical representation of subjectivity and a direct numerical representation using Ex-NRS. We used grayscale images presented to subjective assessment subjects, and VAS and Ex-NRS measured the degree of subjectivity for comparison.