Movement error, pressure variation, and the range effect.

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Abstract
The subject''s (S) task in this study was to compensate for the displacement of a spot of light from the center of an oscilloscope screen. He did this by moving a control stick during a period when the spot was not visible. To determine the effect of pressure variation on the CE and precision (Weber ratio) of positioning responses at small distances, 4 pressure-displacement conditions were used a maximum displacement of 6[degree] with maximum pressures of 0, 7.5, 15, and 30 lb. Eight Ss were used, each serving under all conditions. The displacements were presented in 2 orders: a mixed (random) series and a constant series. For both series, pressure variation had no significant effect on CE and the Weber fraction. The pattern of error and dispersion for the 2 series differed, however. In the mixed series, the range effect was quite prominent as compared to the constant series. Also, the CE at the shortest displacements, when the data of an earlier experiment are included, seems to be greater than the CE at the longest, thus indicating nonlinearity of the range effect. This nonlinearity seems to be exaggerated as the range of movement is shortened. The Weber ratios for the 2 series seem to be proportional except for the initial decline as the extent of movement increases, the mixed series resulting in a steeper fall. Both series show a greater Weber ratio at the shorter displacements, and along with the data of the earlier study suggest that this departure from linearity is magnified by compressing the range of movement.
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