# Motion-Sphere: Visual Representation of the Subtle Motion of Human Joints
## 5 Evaluation of the Proposed Motion-Sphere
### A Comparative User Study  
We selected 13 different ROMs from the TotalCapture data set for visualization on the Motion-sphere (Some of which are demonstrated in Section 4). The study validated parameters, such as the usability, utility, insights, and learnability. The twist quantification, which can only be validated by the user experience is also part of the user study. We compared the Motion-sphere visualization with the video, Motion-belt [17], STS [16] method. The user study included 10 participants aged 20-30 years. All of the participants were everyday computer users. The following procedure was used for the user study. The users were taught about the Motion-sphere visualization, Motion-belt, and the STS technique by providing them with multiple visualization slides with correct answers (swing, twist, and speed) and instructions as a training set. Sufficient time was given until the users were comfortable before the next phase of testing. The second time, different motion visualization slides without any correct answers were given to users and they were asked to predict the correct swing, twist, and speed of the motion just by visualization. Following this, qualitative user experience was captured. The process was repeated for five iterations.  
We found that the users were able to predict the swing with fairly good accuracy as compared to the video and Motion-belt technique. However, we had mixed results when predicting the twist. Although the users opened that color coding the miniature models of limbs was helpful, they could not quite get it accurately in all three techniques. Figure 14 shows the error in the participants' prediction  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sl. No**} & \multirow{2}{*}{**Type of Motion**} & **Ground Truth** & **Measured** & **Standard** \\  & & **(in Degree)** & **(in Degree)** & **Error** \\ \hline
1 & Lower Arm Swing & 118 & 122 & \\
2 & Upper Arm Swing & 183 & 178 & \\
3 & Lower Leg Swing & 105 & 107 & \\
4 & Upper Leg Swing & 108 & 103 & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Swing visualization accuracy of Motion-sphere against the ground truth: the measured swing is with respect to the parent joint segment.  
Figure 12: Swing angle measurement between the target bone segment and its parent bone segment for the ground truth.  
Figure 13: Accuracy of swing visualization w.r.t. the grid size.  
against the ground truth values. We classified speed into Fast, Medium, or Slow. All three techniques fared equally in their visualization of speed.  
When the participants were presented with five sets of motion, each motion comprising two data for comparison, and asked to provide their perceived difference w.r.t. the swing and twist, an average error of \(8^{\circ}\) was noted in STS and \(4^{\circ}\) in the Motion-sphere, as indicated in Figure 15a. The learnability of the Motion-sphere was also tested across multiple iterations. In their qualitative analysis, the users collectively opened that they were more comfortable and felt more in control of their prediction of the parameters at the end of the experiment. Figure 15b, shows the improvement in the accuracy of prediction while using the Motion-sphere in the second iteration.