Experimental procedures
Participants in different centers were tested in identical surrounding settings. The room was lit and noise-proved. A non-rotatable wooden chair was fixed at a certain spot for participants to sit 1.2 meters (m) away from the wall. All goggles are tightened firmly to avoid any kind of slippage. Each kind of goggle carries a high-speed digital camera and a gyroscope to catch the movements of pupils and sense the angular acceleration. Each equipment was calibrated according to the manufacture’s guidelines. We defined the straight-ahead when facing the wall is 0 degree. From this point on, the 15, 25, 35, and 45 degrees was marked. We pre-calculated and draw a perpendicular line of each angle on the wall (Figure 1F). The targets were placed on the perpendicular lines according to the participant’s height. When performing the vertical impulses, participants tilted their heads 45 degrees away while keeping their eyes on the targets at 0, 15, 25, 35, and 45 degrees, respectively.
Searching the best gaze angle, only the vertical semicircular canals were tested. All directional degrees were collected on the two pairs of vertical planes. After distracted the participants’ head 45 degree to the right, we asked them to stare at the targets that placed at 0, 15, 25, 35, and 45 degrees sequentially. At each angle, at least 10 successful impulses were recorded after outliers were excluded. After the right-side experiments finished, we turned their heads to the left, to perform another round of tests.
In contrast, all six semicircular canals were tested with eithervHIT system in the comparison project. We first asked the participants to look straight forward at the target and move the head at ground-parallel plane to test the horizontal semicircular canals. Then we followed the manufactures’ instructions when performing vHIT on LARP and RALP planes. In the VG and Oto systems, we turned the participants’ head 45 degree left or right with the anterior-posterior axis fixed, while their eyes stared at the same target. For the ESC system, we kept the participants’ head at straight-ahead but rotated side- upwards and downwards. To perform the inter-examiner tests on the gaze-angle experiments, we have two independent examiners to performed on the same participants.