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

estimation, a subject first applied a reference force (or angle)acting on the steering wheel in a clockwise direction. The reference was 10.5 N on the isometric steering wheel and 9" on the isotonic steering wheel. Feedback was given on an 11-point scale, with the reference in the middle of the scale. Subjects were told that the reference corresponded to 100.

A subject then applied 11 different test forces (or angles) by applying a force or angle until the pointer was placed at the middle mark of the 11-point scale. The forces or angles required corresponded to 50 per cent, 60 per cent, 70 per cent, 80 per cent, 90 per cent, 100 per cent, 120 percent, 140 per cent, 160 per cent, 180 per cent, and 200 per cent of the reference force or angle. For force, these stimuli ranged from 5.25 N to 21 N while, for angle, they ranged from 4.5` to IS`. After the presentation of a test stimulus, a subject was asked to report a number considered to represent the test force (or angle) in proportion to the reference. The presentation order of the test stimuli was randomized. For magnitude production, a subject first applied a reference force (or angle) by acting on the steering wheel in a clockwise direction. The referencewas 10.5 N on the isometric steering wheel and 90 on the isotonic steering wheel. Feedback was given on an 11-point scale, with the reference in the middle of the scale. The subject was told that this corresponded to 1011. The scale was removed and a number was displayed instead (50, 60, 70, 80, 90 100, 120, 140, 160, 180, or 200) and the subject was asked to produce a force (or angle) corresponding to the given number in proportion to the reference The presentation order of the test stimuli was randomized.

For this experiment, 12 male subjects, aged between 18 and 26 years, took part using a within- subjects experimental design. Subjects attended two sessions with the order of presentation of the force angle, and magnitude estimation, and magnitude production conditions balanced across subjects.

The exponent indicating the rate of growth of sensation was determined by fitting Stevens' power law to the data. With the stimulus and sensation 3.3.2 Results

Exponents for the rate of growth of sensation were obtained from least-squares regression between the median judgements of the 12 subjects for each test magnitude and the actual test magnitude, with the apparent magnitude assumed to be the dependent variable (261. The calculated exponents were 1.14 (force magnitude estimation), 1.70 (force magnitude production), (1.91 (angle magnitude estimation), and 0.96 (angle magnitude production). The median data, and lines of best fit from all subjects, are shown in Figs 8, 9, 10, and 11 for force estimation, force production, angle estimation, and angle production respectively and are compared inFig. 12

The Spearman rank order correlation coefficients between the physical magnitudes and the perceived magnitudes were 0.89 for force magnitude estimation, 0.65 for force magnitude production, 0.89 for angle magnitude estimation, and 0.87 for angle magnitude