Toshisuke Miwa

Thresholds of perception of vibration in recumbent men

The thresholds of perception of vibration by recumbent men are a significant index for the governmental agency concerned with regulation of vibration exposure. The thresholds of perception of continuous sinusoidal vibrations and single and multiple bursts of sinusoidal vibrations in the horizontal and vertical directions were investigated in recumbent men. We found that the threshold curves, as a function of the frequency, had different characteristics for vertical vibrations than for horizontal vibrations in the recumbent position. The threshold values for pulsed vibrations became smaller (easier to perceive) as the bursts were elongated until saturation occurred at 4 s duration. Threshold values for pulse durations longer than 4 s were the same as those for continuous vibration. This suggests the existence of temporal integration of sensation of vibrations as in psychoacoustics.

Evaluation of vertical vibration given to the human foot

The effects of acceleration amplitudes and frequencies of vertical foot vibration on mechanical and sensation responses were studied in two sets of experiments. The first experiments determined the mechanical characteristics of the foot in three seated subjects at frequencies between 5 and 1000 Hz, in terms of the driving point mechanical impedances and acceleration transmission ratios between the foot and lower leg. In the second set of experiments, sensation scales for foot vibrations were determined in ten seated subjects at octave center frequencies between 8 and 400 Hz, which involved equal sensations of continuous and impulsive motions, sensation magnitudes, and rating of five successive categories of sinusoidal motion. Contours of mechanical and sensational responses are presented. Using the results obtained, a foot response meter was made and used in a field survey to evaluate foot vibration.

Evaluation methods for vibrations

Abstract Interval and ratio scales in subjective response were determined for vertical and horizontal sinusoidal vibrations of the whole body in the same way as loudness level and loudness in psycho-acoustics. The sensation difference between vertical and horizontal vibrations was also observed. Next a weighted summation method in the ratio scale was examined for frequency components of compound sinusoidal and random vibrations and an evaluation method for pulsed vibrations studied. The relation between emotional response (unpleasant or intolerable) and sensation magnitude in the interval scale was examined as a possible means of assessing the vibration. Finally, a method of measurement was established for actual vibration given to a person who sat on a soft resilient cushion on a vibrator. This paper is a review of work carried out by the authors.

Slow vertex potentials evoked by whole‐body impulsive vibrations in recumbent men

Characteristics of slow vertex responses evoked by whole‐body vertical and horizontal impulsive vibrations of one cycle of a sinusoid were investigated in recumbent men. Fundamental frequencies were varied from 8 to 100 Hz. The p–p amplitudes and latencies of V potentials were determined as a function of vibration amplitude and fundamental frequency. The response patterns are similar to those evoked by optical and acoustic stimuli to human visual and auditory organs. The thresholds of the evoked potentials were determined by a cross‐correlation technique and the perceptional thresholds were measured for the same vibration. It is concluded that the perceptional thresholds can be estimated approximately from the thresholds of the evoked potentials, for example, by subtraction of 14.5 dB from the thresholds of the evoked potentials for vertical vibrations and 10 dB from those for horizontal vibrations from 8 to 100 Hz.