# The Effects of 3D and 2D Imaging on Brain Wave Activity in Laparoscopic Training
## 2 Methods
### Apparatus  
Both tasks were conducted in a laparoscopic simulation trainer (40 cm \(\times\) 25 cm \(\times\) 15 cm, length \(\times\) width \(\times\) height) developed for the present study. Simulated laparoscopic tasks were performed by holding a laparoscopic instrument passing through a rubber diaphragm representing the patient' abdominal wall. The port of 10 mm in diameter was located at 5.7 cm and 135\({}^{\circ}\) from the center of the rubber diaphragm, and the fulcrum was located approximately halfway up the instrument shaft. The handle of the instrument was set at 80% of the participant's elbow height, as suggested by [PERSON] et al. [34]. A horizontal occluding board was used to prevent direct vision of the instrument displacement during the tasks. Many previous studies comparing 3D and 2D vision systems have failed to use appropriate controls that were identical in all respects except for the 2D or 3D viewing conditions [35]. To ensure that 2D and 3D viewing were the only variables in this experimental research comparing laparoscopic technical performance and mental workload in 2D and 3D, the display monitor and laparoscopic camera were kept identical by using one vision system that was able to display both 2D and 3D images with the same set-up. For both the 2D and 3D viewing conditions, the participants controlled the movement of the instrument based on visual feedback from a 3D TV (Sony KDL-55W800B 55-inch 3D LCD TV). A 3D digital recorder (Sony HDR-TD30V Full HD) was set at an angle of 30\({}^{\circ}\) from the horizontal plane to capture real-time displacement movement in the laparoscopic simulation trainer for synchronous display on the 3D TV. For the 3D viewing condition, the participants wore active 3D glasses (SONY TDG-BT400A) to view the stereoscopic 3D images. Suboptimal viewing conditions caused by head tilt from the display elevation and acute eccentric viewing angles increase crosstalk due to incorrect orientation of the glasses relative to the display [36; 37; 38]. 3D perception is dramatically influenced by the distance between the viewer and the stereoscopic display in a way that is qualitatively different from the effect of viewing distance on the perception of a 2D display [35], and the best 3D images are obtained when the viewer is directly facing the display and the viewer's eye level is the same as that of the center of the display [36]. To ensure fair comparisons between the 2D and 3D displays, the viewing conditions were standardized by adjusting the screen height according to each participant's eye level and maintaining an eccentric viewing angle of 90\({}^{\circ}\) and a viewing distance of 2 m from the participant's eyes, as shown in Figure 1.  
A pegboard and triangle set (Limb & Things, Product No. 50331) and a 5 mm curved dissector were used in the peg transfer task (shown in Figure 2). A digitizer tablet with a light and accurate pen (Wacom CTL-480) and a 10 mm Endo Babcock clamp were used for the circle-tracing task. As shown in Figure 3, the digitizer tablet was covered with a target paper with a pre-marked circular path, and the Endo Babcock clamp was modified by removing the clamp and attaching the digital pen to the rod of the instrument with a plastic tube. The MUSETM headband (InteraXon Inc., Toronto, Canada), a commercially available and noninvasive wireless Electroencephalography (EEG) monitor, was used to collect brain waves and blinks at a sampling rate of 220 Hz. It is worn as a flexible, adjustable, lightweight headband with seven sensors--two forehead sensors, two ear sensors, and three reference sensors--and has been used in previous studies [39; 40; 41; 42; 43]. Participants wore the headset while performing the two tasks and the data were transmitted via Bluetooth to a laptop. Once the simulated task was completed, the NASA TLX form was used to evaluate the subjective mental workload experienced by the participant.