Psychophysical Assessment of Whole-Body Vibration

Using the methods of magnitude estimation and intensity matching, curves of equal subjective vibration intensity were constructed over the frequency range from 3.5 to 20 Hz. Twenty subjects made magnitude estimations of the intensity of vibration at 0.08, 0.16, 0.24, 0.40, 0.48, and 0.56 gz with vibration at 0.32 gz serving as a standard. These intensities were judged at each of the frequencies of 3.5, 5, 7, 9, 11, 15, and 20 Hz. For each frequency, the results were plotted as straight-line functions on log-log graphs of subjective intensity against physical intensity. The slopes of the lines varied as a function of frequency, the steepest slope occurring at 5 Hz. (the frequency of greatest body response due to resonance in this axis). Additional experiments were conducted in which ten subjects matched the intensity of 9-Hz. vibration at 0.16, 0.36, and 0.56 gz with vibration at each of the other six frequencies listed above, and ten different subjects made similar equality judgments against 9-Hz. vibration at 0.08, 0.26, and 0.46 gz. Equal intensity curves derived from the magnitude estimation data show the same general shape and comparable levels as corresponding curves determined experimentally using the intensity matching procedure. These methods provide more systematic and quantitative characterizations of subjective response to vibration than previous approaches which have relied heavily on qualitative descriptions.