Systematic Alterations of the Apparent Centers of Lines

Abstract

Predictable stimulus-bound alterations in the apparent centers of lines were used to discriminate behavioral differences in bisection. 2 dimensions of individual differences were demonstrated in bisection that appeared to be related to cognitive control mechanisms: the well-known basic tendency for the upper segment of lines to be overestimated, and the relative influence on the apparent centers exerted by the stimulus-effects. The roles on these of minor modifications in the stimulus and of secondary factors such as practice, eye and hand dominance, sex, etc., were examined. A more basic effect was noted when the lines were bisected in a horizontal orientation—there was almost no correlation between S's performance with vertical vs horizontal lines. Even though the two main effects noted above were still present, their measures did not correlate with those of the vertical bisection. The implications of this are discussed.