**4. Experimental methods**

170 Advanced Topics in Measurements

plates vertically to control the step-height. The servo motor-driven X-table generates the presentation velocity by its reciprocating movement. The rotary table regulates the presentation angle by rotating the X table placed on it. The Peltier elements maintain, using the Peltier effect to heat or cool, the step plates' temperature by regulating the DC voltage applied to them. Here, the presentation angle of the step plates to a subject's finger is controlled as shown in Fig. 7. The motion direction of the X-table is always perpendicular to the direction of a step edge. Consequently, the presentation device is capable of presenting a fine step-height at the reciprocating velocity of 0 to 60 mm/s and the presentation angle of 0 to 180 degrees. In addition, the step plates' temperature can be controlled within the range

Angle: 0 Angle: 45 Angle: 90

In the psychophysical experiments using the measurement system, when the human subjects are required to judge which step-height of the presented step pair is larger, they press each of the right/left computer-mouse buttons to input the answer into the computer. The step-heights of the next trial are calculated by computer based on the PEST algorithm

In the passive-touch experiments of this paper, a cover plate with a hole like fingertip profile was installed to cover the step-height presentation device as Fig. 6 showed and the human subjects touched the step plates through the hole using their top and center of their fingertips as shown in Fig. 8. During the experiments, to prevent the sensitivity of human tactile sensation from declining, the step plates' temperature and the room temperature were kept constant approximately 37 and 26 degrees centigrade, respectively. Before the

Top of fingertip Center of fingertip

experiments the human subjects washed their hands with soap to keep them clean

of 8 to 50 degrees centigrade.

Fig. 7. Presentation angles of step.

using the subject's answers.

Fig. 8. Fingertip regions.
