Note on the systematic error of estimation as a function of stimulus magnitude.

Abstract

On the basis of a discussion of Weber's law the prediction was made that the systematic errors of estimation are linear functions of stimulus magnitude. As a special case it is suggested that the size of a geometrical illusion generally is a linear function of the size of the illusion figure. The result of an experiment with Oppel's illusion is in agreement with this prediction.—During successive estimations practice did not decrease the amount of illusion.