## 3 Psychophysical Experiments
### Experiment 2
#### 3.5.2 Experimental Results  
The average recognition accuracy and reaction time from all total trials was about 95 percent (SD:11 percent) and 1.02s (SD: 0.52 s) as illustrated in Figure 9. It can be seen that in all conditions, the coding method with combination of three parameters performed better than that of two parameters. To quantitatively analyze the preference of combinations in terms of recognition accuracy, post hoc tests with Bonferroni were performed.  
In order to intuitively compare the performances of all the coding methods considering both recognition accuracy and reaction time, we further carry a ITR analysis as illustrated in Figure 10.  
As seen in Figure 10, there is a significant effect of CM on ITR, and LRM has the highest ITR among the proposed coding methods, which is in accordance with results of ANOVA analysis (Table 4).  
Figure 8: Schematic diagram of coding methods with combination of three parameters: (**a**) location, rhythm of times and intensity (LRI); (**b**) location, rhythm of duration and intensity (LRI2); (**c**) location, rhythm of times and intensity (LRI3); (**d**) location, rhythm and mode (LRM). For the convenience of labelling angel intervals, five degrees in vertical coordinate indicates the interval [5; 10] in Table 3, 10 indicates [10; 15] and so forth.  
Figure 9: Recognition accuracy and reaction time (s) for each coding method in experiment 2. Error bars indicate standard error.  
In order to further improve the recognition accuracy of the vibrotactile display. We carry a three-way repeated measure MANOVA to study whether there is significant difference of performance between levels of each coding parameter in the preferred coding method (LRM). There are four independent variables: flight states (four levels), locations (five levels), rhythms (two levels), and one dependent variable: recognition accuracy.  
As seen in Table 4, there are no significant difference of performance between levels of each coding parameter, except for the parameter of location (\(F_{(19,4)}=2.97\), \(p=0.032\)). In order to further improve the design of vibrotactile device and its coding strategy. We analysis the correct percentage changing with the set angle as shown in Figure 11.  
As seen in Figure 11, the average recognition accuracy of all the angles exceeded 90%. The recognition accuracy at the angles ranging from 20 to 40 degrees and 60 degrees appear to be greater in terms of volatility than other angles. These angles were cued by t  
\begin{table}
\begin{tabular}{c c c c} \hline
**CM(0)** & **CM(0)** & **Mean Difference/I-J(Z)** & **Sig** \\ \hline LR & LRI1 & \(-0.17367\,\)* & \(0.004\) \\ LR & LRI2 & \(-0.00610\) & \(0.916\) \\ LR & LRI3 & \(-0.11890\,\)* & \(0.043\) \\ LRI1 & LRI2 & \(0.17976\,\)* & \(0.000\) \\ LRI1 & LRI3 & \(0.05476\) & \(0.219\) \\ LRI2 & LRI3 & \(-0.12500\,\)* & \(0.007\) \\ PRM & PRI1 & \(0.01424\) & \(0.694\) \\ \hline \end{tabular}
* represents the mean difference is significant at the 0.05 level.  
\end{table}
Table 4: Post hoc Test for different combinations of coding parameters with LSD correction.  
Figure 11: The curve of recognition accuracy change with set angle in preferred coding method. Error bars indicate standard error.  
Figure 10: Information transfer rate for different coding methods; the error bars indicate standard error.  
respectively (see Figure 2). The questionnaire also indicates that most of the subjects reported that they have difficulty in discriminating vibrations from these factors, which is in accordance with the result of Table 5. It suggests that the setting sites for these factors should be adjusted to further improve the perceptual performance of the vest.