Seated subjects matched their perceptions of the intensity of Y-axis, Z-axis, or Y-plus-Z vibrations, by adjusting the intensity of a sinusoidal, 5-Hz, X-axis response vibration. Stimuli were sinusoidal at 3.2, 5, and 8 Hz. For each frequency there were six vibration conditions (Y axis alone, Z axis alone, or both axes together with 0 degrees, 90 degrees, 180 degrees, or 270 degrees phase angles between them) presented at each of two acceleration levels (0.15 and 0.25 G R.M.S.). Results showed that X-axis response accelerations for the dual-axis stimuli were greater than those for either one of their Y-axis or Z-axis components. This occurred for both acceleration levels and for all three frequencies. In addition, response acceleration was nearly constant for the dual-axis stimuli regardless of the phase angle between their Y-axis and Z-axis components. Again, this was true for both acceleration levels and all three frequencies. These findings indicate that although dual-axis vibrations are judged to have greater subjective intensity than either of their single-axis components the phase relationship between those components appears to have no appreciable effect.
