Intensity judgments of vibrations in the X axis, Z axis, and X-plus-Z axes

Seated subjects matched their perceptions of the intensity of X-axis, Z-axis, or X-plus-Z vibrations, by adjusting the intensity of a sinusoidal, 5 Hz, Y-axis response vibration. Stimuli were sinusoidal at 3.2, 5, and 8 Hz. For each frequency there were six vibration conditions (X axis alone, Z axis alone, or both axes together with 0 degree, 90 degrees, 180 degrees, or 270 degrees phase angles between them) each presented at each of two acceleration levels (0.15 and 0.25 G.R.M.S.). Results showed that Y-axis response accelerations for the dual-axis stimuli were greater than those for either one of their X-axis or Z-axis components. This occurred for both acceleration levels and for all three frequencies. However, the pattern of results indicated that response acceleration varied significantly as a function of the combination of phase angle and frequency. This is in contrast to results from a previous experiment, involving Y-plus-Z axis stimuli, which showed that the effects of phase angle were minimal at all three frequencies. Apparently phase angle, in combination with frequency, plays a significant role for X-plus-Z vibrations, but not for Y-plus-Z vibrations.