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.