## 6 Experiments and Discussion
### Preliminary Experiment
#### 6.1.5 Discussion and Suggestions for Next Experiment  
In the preliminary experiment, the material was perceived only by the enlarged image of the texture and the impact sound, and the shape of the object was only the cube.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Actual Class** & **Accuracy** \\ \hline cloth & 0.80 \\ glass & 0.61 \\ metal & 0.73 \\ paper & 0.67 \\ plastic & 0.51 \\ wood & 0.63 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Accuracy for each material class.  
Figure 16: Example of displayed cubes.  
Figure 17: Displaying cubes for each material in VR.  
Therefore, we concluded it was difficult to distinguish the material, because the situation was different from the normal perceptual situation. There was a similar feeling from the subjects, based on their responses after the experiment.  
However, even under the same circumstances, there were four or more patterns of all materials, with a correct answer rate of 80% or more. This result suggests that even if only the texture image is presented, it is sometimes possible to perceive with some accuracy, depending on the combination, and that there is a difference in each combination of materials.  
Therefore, in the preliminary experiment, the combination, in which the accuracy was 80% or more, was used as the combination capable of correct perception. Table 7 shows the patterns selected, based on this criterion for each material, where the combination of incorrect materials selected for the correct material is indicated by \"-\", and each pattern is separated by \",\".  
The next problem was the difference in the accuracy rate for each subject. Just as the accuracy differs, depending on the combination of each material, it is possible that each subject has individual differences in their perceptual ability. Therefore, Table 8 shows the accuracy of all materials of each subject for the same material patterns as Table 7.  
As we can see here, excluding subjects E and H, all subjects achieved an accuracy of 80% or more, in all selected combinations. We compared the average value of the accuracy of each material for each group, between the subjects whose accuracy was 80% or more, and those whose was not (that is, subjects E and H). The results revealed a significant difference (\(p=0.0281<0.05\)), indicating that there is a difference in perceptual ability in the preliminary experiment between these two groups.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Actual Class** & **Patterns** \\ \hline cloth & glass-metal, glass-plastic, glass-wood, metal-paper, metal-wood, paper-plastic, plastic-wood \\ glass & cloth-metal, cloth-paper, metal-paper, metal-wood \\ metal & cloth-paper, cloth-plastic, cloth-wood, glass-paper, paper-plastic, paper-wood \\ paper & glass-metal, glass-wood, \\ plastic & cloth-glass, cloth-paper, \\  & cloth-wood, glass-paper \\ wood & cloth-metal, glass-plastic, \\ \hline \hline \end{tabular}
\end{table}
Table 7: Combinations capable of correct perception.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Subject** & **Accuracy of All Materials** \\ \hline A & 0.828 \\ B & 0.828 \\ C & 0.828 \\ D & 0.862 \\ E & 0.724 \\ F & 0.859 \\ G & 0.931 \\ H & 0.682 \\ I & 0.931 \\ J & 0.897 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Accuracy of all materials of each subject.  
On the basis of the above, we selected the subjects with the combination of materials shown in Table 7 and the accuracy of 80% or more in Table 8 and conducted the following experiment.