The sinusoidal vibration sensation at lying on the back was equalized into that at sitting by 10 male subjects in the frequency range between O.5 and 300 Hz, in order to obtain equal sensation contours at lying posture. This experiment was carried out for the vertical and the horizontal vibrations.

As a result, the vertical vibration sensation of the lying subject receiving from 40 to 150 Hz was severer by about 12 dB in max. than that at sitting, because of the resonance of the skull. On the remainder frequency range, vibration perception was almost the same at both postures. On the other hand, the horizontal vibration sensa-tion at both postures was nearly the same in all frequency range (0.5-300 Hz). From these results, the equal sensation contours at lying posture for both directional vibra-tions were determined.

The estimated equal sensation curves from above results agree with those obtained by direct measurement in which the vibration at a certain frequency from O.5 to 300 Hz was equalized into the standard vibration at 20 Hz. Thus, the assessment method of the vibration at the sitting posture established previously can be applied to that at the lying provided that the equal sensation contour for the vertical vibration is revised near 80 Hz.