Subjective effects of combined-axis vibration: comparison of Y-axis and Y-plus-roll vibrations

A psychophysical matching experiment was conducted to compare the perceived intensity of Y-axis and Y-plus-roll vibrations. Seated subjects matched their perceptions of the intensity of single-axis stimulus vibrations in the Y-axis, or combined-axis stimulus vibrations made up of Y-axis and roll motions, by adjusting the intensity of a sinusoidal, 5 Hz, Z-axis response vibration. Stimulus vibrations were sinusoidal at 3.15, 4, 5, 6.3, and 8 Hz. For each frequency, both types of stimulus vibrations were presented at three acceleration levels related to three axis-to-seat distances for the roll vibrations. The results showed that as frequency increased the acceleration of the Z-axis matching response decreased for both types of stimuli. In addition, as stimulus acceleration (axis-to-seat distance) increased, response acceleration showed substantial increases at every frequency. However, the matching responses showed only minor differences due to vibration type, indicating that the effects of roll vibrations can be accounted for in terms of the Y-axis translational vibrations produced at the subject's seat.