Experiments have been carried out to determine the sense of horizontal vibration where subjects can see the view from a window. A gap between physical feeling and visual amplitude of vibration can cause discomfort and an uneasy feeling in the high frequency and acceleration range. The visual situation has the greatest influence on vibration perception, and this is closely connected with vibration amplitude. Vibrations can not be perceived physically in the low frequency and small acceleration range, but they can be recognized visually as movement of the view. Therefore, many subjects can perceive vibrations when they can see the view. It is therefore necessary to assess the perception threshold in consideration of the influence of visual sensation. The visual sensation does not influence perception in the high frequency range, because the vibration amplitude is imperceptible in that range. It is therefore possible to assess vibrations on the basis of perception threshold scatter by physical feeling in the body.
