In previous reports of this series, psychological experiments have been carried out on subjects sitting on a vibration table without cushions. In the case sitting on a cushion, vibration influence may be assessed either by measuring vibration acceleration values at the most adjacent spots on body surface touching the cushion, or by obtaining them by subtracting the attenuation values of the cushion from the vibration spectrum given to the subject without it. As the latter is capable of pursuit by several techniques in the laboratory test, measuring methods of the attenuation effect of the cushion are studied in this report.

Three methods, threshold shift, mechanical impedance and acceleration ratio, were devised for the measurement of attenuation effect of the cushion to vertical and horizontal vibrations in frequency range between 2 and 100 Hz. Patterns of the attenuation effect on two resilient samples were determined for both vibrations using these methods. Measuring method of the vibration spectrum directly given to the subject sitting on the resilient material was also deduced for practical use.