**6. Conclusion**

In this study, to measure the finger's fine step-height discrimination capability the computer-controlled measurement system that presents fine step-heights of 0 to 1000 µm to subjects' fingers was developed. Using the measurement system the paper examined the effects of the touching manner of human finger, finger's motion direction, and fingertip region on the tactile recognition of fine step-heights. In the psychophysical experiments, to determine the difference thresholds and subjective equalities for fine step-heights the measurement system calculated the amounts of step-height of the step pairs by computer according to the PEST algorithm and presented the step pairs to the subjects.

First, the upper thresholds for the step-heights of 10 to 100 µm were determined in the active- and passive-touch experiments. The resulting thresholds became larger as the magnitude of step-height increased. Also the threshold of active-touch manner for each of the step-heights larger than 50 µm was smaller than that of passive-touch manner and the thresholds of the touching manners for each of the step-heights smaller than about 40 µm were almost equal regardless of the touching manners. Therefore it was found that the fingertip's discrimination ability of the fine step-heights depends on the amounts of stepheight and if a step-height is larger than 50 µm, the finger's tactile sense can increase the sensitivity in active-touch manner.

Next, to investigate the effects of the finger's motion direction and fingertip region in recognizing fine step-heights, the upper thresholds for a 10 µm step-height were determined when the human subjects discriminated the pairs of step-heights presented at various presentation angles using the top and center of their fingertips. When the presentation angle of a step-height to a fingertip changed from 0 to 90 degrees, although the thresholds of the center of the fingertips almost stayed constant, the threshold for the step-height presented to the top of the fingertips at 90 degrees became the smallest value. Therefore, it was found that the tactile sense of the top of a fingertip is highly sensitive to the step-height as compared with that of the center.
