2.2 Methods
For this study, we improved the electric goniometer (NAGASHIMA MEDICAL
INSTRUMENTS co., Ltd.) so that we did not monitor any other position
(for example, up-and-down of the center of gravity) except for tilt
stimulation, and that the movement could be stopped with a joy-stick
immediately when volunteers perceived a level of tilt. We were also able
to measure the tilt angle from the standard level with a digital display
of the tilt angle.
There is a direct-current motor behind the tilt bedplate. This motor
connects a right and left changeover switch of the tilt direction, and
has a potentiometer that displays the angle and enables measurement to
0.1°.
It is possible to tilt the subject to a maximum of
20°on both sides, and to change the angular velocity.
This enabled us to maintain the experimental conditions better than the
past manual studies and allowed for easy and objective measurement, in
contrast to the past studies because of the digital display of the tilt
angle.2-4
We studied the tilt perception and very short term memory of the tilt in
normal volunteers in standing and sitting positions as a pilot study. We
found that the sitting position to be more difficult than the standing
position. Therefore, we decided to study the patients in a sitting
position, and set up the chair on the tilt bedplate of the electric
goniometer (Figure 1). We made volunteers sit in the chair without
leaning against the backrest. We covered their eyes with goggles to
remove the visual input and used an instrument fixed to the trunk, and
fixed their head in place with ear pads attached to the chair. Patients
were also required to take off their shoes and float both of their legs
(Figure 2). We regulated the angular velocity of the tilt at
1°/sec.