Visual extrapolation of a line segment to the point of its intersection with a straight line. I.

A study is made of the capacity of fifty subjects to estimate the position of the point of intersection between a straight line and the visually extrapolated extension of a line segment at three different angles between the line and the segment: 30 degrees, 60 degrees and 90 degrees. The results show systematic deviations in the estimation of acute angles. The point of intersection of the straight line and the segment is misperceived to be shifted inwards in the angle between them. It is also shown that the set of imaginary extensions of a line segment with a given length, until its intersection with the given straight line, is determined only by the angle between the straight line and the segment and does not depend on the distance between them. Various possible mechanisms which could determine the solution of the task facing the subjects are discussed.