┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 装 ┊ ┊ ┊ ┊ ┊ 订 ┊ ┊ ┊ ┊ ┊ 线 ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊

subjects would match either the displacement of the hand on the steering wheel or the angle through which the steering wheel was turned. 'match the sensation experienced with the reference wheel. Subjects were required to achieve the reference or match within 6 s, and to hold the force or angle for 4 s. Subjects were required to move their hands to the test condition within the 6 s given to achieve the match. The total time for one reference and match trial was 20 s

Subjects attended two sessions, one with isometric steering wheels and one with isotonic steering wheels. Four reference conditions were presented in each session: 5 N, 15 N, 1.5 N m, and 3 N m with the isometric steering wheels, and 3`, 90, 10 mm, and 30 mm with the isotonic steering wheels. The forces and distances refer to the forces and dist-es at the hm of the steering wheel.

For this experiment, 12 male subjects, aged between 18 and 26 years, took part using a within-subjects experimental design where all subjects participated in all conditions. The order of presentation of the reference conditions was balanced across subjects

For six subjects, the first session used the isometric steering wheels; for the other six subjects, the first session used the isotonic steering wheels

For each reference condition, a total of 18 trials were undertaken: nine trials to account for each combination of three reference wheels and three diameters of test wheel (small, medium, and large) including matching to the same wheel, and a repeat of these nine conditions.

The length of time that subjects were required to hold a force or torque was minimized to prevent fatigue. Typically, subjects took 10s to reach the desired force or angle. The view of their hands was obscured so that subjects did not receive visual feedback of their position or movement.

3.1.1 Method

Using the 'method of adjustment' [11l, subjects 'matched' sensations from a 'reference' steering wheel to a 'test' steering wheel. When grasping the reference wheel, subjects were required to achieve a desired stimulus magnitude师acting on the wheel in a clockwise

direction using visual feedback from a fixed 11-point indicator scale on a computer monitor. Instructions on the computer monitor then instructed the subjects to move their hands to either the'small','medium; or'large steering wheel, and to The results for a typical subject in the experiment with isometric control are shown in terms of force in. The results for a typical subject in the experiment with isotoniccontrol are shown in terms of angle in Fig. 4 and in terms of displacement in Fig. 5

Correlation coefficients between the physical magnitudes of the reference condition and the test condition are presented for each subject in Table 1 For isometric control,

correlation coefficients were obtained for both torque and force at the steering- wheel rim. For isotonic control, correlation coefficients were obtained for both angle and displace