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Difference thresholds for lifted weights have been reported by Laming .based on an Experiment Fechner using weights from 300 to 3000 g, resulting in a Weber fraction of 0.059 (5.9 per cent), and Oberlin [151 measured difference thresholds for lifted weights from 50 to 550 gaving a Weber fraction of 0.043 (4.3 percent)

tic discrimination of finger span with widths varying from 17.7 to 100 mm have been reported as 0.021 (2.1 per cent) by Gaydos h61. Discrimination of elbow movement has been reported as 8 per cent by Jones et al. [17], while discrimination of sinusoidal movements of the finger studied Rinker et al. produced difference thresholds that ranged from the present experiment investigated difference thresholds for steady state steering-wheel force(using an isometric steering wheel), and difference thresholds for steady state steering-wheel angle (using an isotonic steering wheel). 3.2.1 Method

Difference thresholds were determined with a two alternative forced-choice procedure using an up-and-down transformed response (UDTR) method. Subjects were required to act on the steering wheel to achieve a reference force or reference angle, followed by a test stimulus. The required levels for both actions were presented on a character-less 11-point scale on a computer monitor. The reference stimulus and a test stimulus were presented sequentially, and in random order, to subjects who were required to report which of the two stimuli 'felt greater: The UDTR method was used with a three down one-up rule (i.e. three correct responses row caused the test stimulus to become closer to the reference stimulus whereas one incorrect response resulted in an increase in the difference between the reference and the test stimulus). The three-up one down rule means that the observed at a 79.4 percentdictated their responses. The sequence terminated after three 'up' and three 'down' reversals of direction. The difference thresholdwas measured as the mean value of the last two 'up' and the last two 'down' reversals.

For this experiment, 12 male subjects, aged between 18 and 28 years, took part using a within-subjects experimental design. The order of presentation for the refer-- conditions was balan-d across sub- jects with six subjects starting with isotonic control, and six starting with isometric control. 3.2.2 Results

The median absolute and relative difference thresh olds are shown in Table 2. For both force and angle, the absolute difference thresholds increased signifi- cantly with increasing magnitude of the reference(p < 0.01, Friedman test)

The median absolute and relative difference thresh- olds for both force and angle are shown in Fig. 6 andFig. 7 respectively. The median relative difference thresholds tended to decrease (from 16.5 per cent to 11.5 per cent) with increases in the reference force and decrease (from 17.0 per cent to 11.5 per cent)with increases in the reference angle. However, over-all, the relative difference thresholdsd not differ significantly over the three