## 2 Experiment 1
### Results and Discussion  
#### 2.2.1 MLDS Analysis  
The results, as shown in Figure 2a, are consistent with the intuitive guess that the larger the index number difference, i.e., the greater the gloss difference, the higher the probability of subjects choosing that pair of materials. Consequently, the blocks located further from the diagonal in the figure correspond to a higher probability of choice. By observing a series of material pairs with equal serial number differences (the series of blocks parallel to the diagonal corresponding to material pairs), such as only comparing all material pairs marked with black dots (the index number difference is 1), it is found that the higher overall gloss (8 and 9 have higher overall gloss than 1 and 2), the higher probability of being selected, indicating that subjects are more likely to perceive greater gloss differences even though these material pairs have similar gloss differences on physical axes. Figure 2b shows the data of the Virtual group in a similar way. The results of the Virtual group are generally the same as those of the Real group.  
After conducting MLDS analysis, the glossiness psychological scale image for the Real group is shown in Figure 3a. From an overall perspective, the relative perception intensity increases monotonically with actual glossiness; however, the relationship between them does not change linearly, especially in the 20 GU-30 GU interval, where lower glossiness perception intensity occurred than in slightly higher glossiness situations. This phenomenon can also be observed in Figure 2a, where the combination of (3, 4) exhibits a lower probability compared to other combinations with a difference of 1 in their corresponding index values. This shows that people are not sensitive to glossiness perception in this interval, and it is difficult to reflect perception differences in data by adding some error disturbance. However, in the high glossiness interval, perception intensity rises very quickly, and the same increase in glossiness brings a relatively larger change in perceived glossiness.  
Figure 2: The original data before MLDS analysis. (**a**) shows the original data of the Real group. (**b**) shows the data of the Virtual group. The glossiness intensity (index number) of the stimuli is sorted from low to high. The different color brightness in the figure represents the probability of subjects choosing the stimulus pair composed of horizontal and vertical coordinate intensities. Different marker represents the index number difference between different stimulus pairs.  
Figure 3b depicts the data analysis outcome of the Virtual group. Notably, the perception in the medium gloss range is not particularly sensitive, whereas the perception outcome in the high gloss range is more influenced by the actual gloss. However, the characteristics of the extremely low gloss range (i.e., approximately 0.0-0.3) in the Virtual group are more salient, similar to the changes in the high gloss range, with a steeper incline. The nonlinear relationship of the virtual group is relatively clearer, exhibiting a growth pattern similar to that of a quadratic function, but it can also be divided into three ranges: low, medium, and high, each with its unique characteristic change. Within the low-gloss range (i.e., from 0.0 to approximately 0.3), the perceived glossiness increases at a faster rate, then transition to the medium-gloss stage, and the sensitivity to glossiness alterations visually diminishes. The glossiness within the range of 0.3 to 0.6 is compressed in perception. After 0.6, the perceptual response to glossiness becomes sensitive again, and minor alterations in glossiness can result in a notable perceptual response.