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.