## 3 Materials and Methods
### Materials  
In this study, two stimuli (modeling techniques) were designed: conventional parametric CAD modeling and VR free-form modeling (see Table 1). Parametric CAD modeling has been extensively used in different fields. Because of its widespread usage, the SolidWorks modeling software (2016 version) was employed for the parametric CAD modeling in this study. ASUS computers equipped with an NVIDIA discrete graphics processing unit and a 20-inch, light-emitting-diode screen were used in the parametric CAD modeling experiment. The computers were located in the computer room of a school.  
\begin{table}
\begin{tabular}{c c c} \hline
**Item** & **Parametric CAD** & **Free-Form VR** \\ \hline \multicolumn{2}{c}{Operative technique} & Desktop & VR devices \\ \hline \multirow{3}{*}{Hardware} & ASUS desktop computer, LED display screen, keyboard, and mouse. & HTC VIVE Pro, a handheld controller, a base station, and an Acer VR-ready laptop \\ \hline \multirow{6}{*}{Specifications} & Display: 20-inch, light-emitting-diode (LED) screen & Display: Dual AMOLED 3.5” screens \\  & Maximum resolution: 1366 \(\times\) 768 pixels & Resolution: 1440 \(\times\) 1600 pixels per eye (total 2880 \(\times\) 1600 pixels) \\ \cline{1-1}  & Viewing angle: (horizontal and vertical) & 2880 \(\times\) 1600 pixels) \\ \cline{1-1}  & 90 \(\times\) 65 degrees & Field of View (FOV): Approximately 110 degrees \\ \cline{1-1}  & Graphics processing unit: The desktop computer equipped with an NVIDIA discrete graphics processing unit & Refresh Rate: 90 Hz \\ \hline \multirow{2}{*}{Software} & SolidWorks 2016 & Gravity Sketch 3D VR \\  & (executed on Microsoft Windows) & (activation of SteamVR on Microsoft Windows) \\ \hline \multirow{6}{*}{Operation site} & \multirow{2}{*}{\begin{tabular}{c} \begin{tabular}{c} \begin{tabular}{c} \begin{tabular}{c} \begin{tabular}{c} \begin{tabular}{c} \begin{tabular}{c} \begin{tabular}{c} \begin{tabular}{c} \begin{tabular}{c} \begin{tabular}{c} \
\begin{tabular}{c}
\begin{tabular}{c} \end{tabular} \\ \end{tabular}\end{tabular}\end{tabular}\end{tabular}\end{tabular}\end{table}
Table 1: Descriptions of the conventional parametric CAD modeling and VR free-form modeling.  
VR free-form modeling is an emergent modeling technique, and Gravity Sketch 3D was used as the software for VR free-form modeling in this study. In this creative 3D modeling software, a polygon modeling technique is used to connect points, edges, planes, and entire elements. Gravity Sketch 3D has features such as a 3D space brush, color selection system, and VR modeling controller, and this software enables designers to model their products by using a handheld VR controller. During testing, the participants put on a head-mounted display (HTC Vive, HTC and Valve Corporation) and used a wireless handheld controller (SteamVR, Valve Corporation) for operation. The examiners activated the motion program of SteamVR on a 15-inch, VR-ready Acer laptop with the Microsoft Windows operating system to monitor the experimental process.  
The participants had to complete two modeling tasks in each modeling technique: (1) the modeling of an exact geometric shape, namely a cube, and (2) the modeling of a creative shape, namely a mug. A cube is a basic geometric shape with simple and symmetrical characteristics and its modeling requires precise size control. A mug has a free, creative shape, and its modeling process is more complex than that of a cube.