The pressure exerted by the index finger tip was continuously recorded while the human subject was trying to maintain the pressure at the level of a given pressure (this pressure is named ‘target pressure’, 0.5-500g) with optical information for ten minutes, and the results obtained under various conditions were analysed.
1) The errors tended to be minimal in the range between 40 and 50g target pressure, and increased approximately in proportion to the target pressure above 50g.
2) When the subject relaxed his index finger, the errors decreased with decreasing target pressure in the range of less than 50g.
3) The errors were increased by excluding optical information. In target pressure less than 50g, the increment of the errors due to a decrease in the skin pressure intensity was further increased by exclusion of optical information.
4) In small target pressures, the errors tended to decrease transiently in evening, while in large target pressures the errors showed a gradual increase from morning toward evening.
5) The errors showed generally minimal values 2 or 3 minutes after the beginning of the measurement, and thereafter increased more remarkably in large target pressures than small ones.

The effects of the surface friction of a grasped object on the regulation of grip force during holding tasks using a precision grip were investigated. Using a force transducer-equipped grip apparatus, the grip force and load force acting on the object were measured continuously while surface materials (silk, wood, suede and sandpaper) and load weights (0.98N, 1.96N, 2.94N, 4.90N and 9.81N) were varied. From the recorded data, the average static grip force, slip force, safety margin force and static friction coefficient were evaluated.
It was found that both the slip force and safety margin force increased as the slipperiness of the object surface increased. Significant interactions between surface type and weight were observed in the slip force and static friction coefficient. The interaction effect resulted from the fact that the frictional relationships with the fingers changed according to both weight and surface conditions. This was considered due to the viscoelastic nature of finger skin. An increase in the safety margin force with surface slipperiness was considered due to psychological reaction, probably fear of dropping the object. Unexpected changes in surface conditions caused a greater safety margin force than trials without a surface change, which might also have been associated with psychological reaction to uncertainty of the new surface condition. A relatively large inter-subject variation was found in the slip force and safety margin force relative to slippery surfaces.

The authors carried out neurometry and CMI investigation on 512 subjects in June and July '87. The subjects were devided into four groups according to the CMI criteria by Fukamachi: CMI. I Diagnosed to be normal, II Provisionally to be normal, III Provisionally diagnosed to be neurotic, IV Diagnosed to be neurotic. Comparison was done not only among these groups, but also among age groups and between male and female.
Although there were no great differences among the group I, II and III, each current through F2, F4, F5 and F6 significantly decreased from the group I to IV (p<0.01). A similar tendency was seen in F2 and F6 of the male subjects in each age group, but no tendency in the female subjects.