Fig. 5.

Statistical explanation of the tilt illusion. (A) Probability distribution of the physical sources of projected angles in the database, given a reference line oriented 60° from the horizontal (indicated by black in the icons below the graph). (B Left) Standard presentation of the tilt illusion, as shown in Fig. 1B; the gray line is vertical. (B Right) The direction (arrows) and magnitude of the tilt effect predicted by the distribution shown in A. The solid gray line is vertical; the dotted line indicates the predicted shift in the apparent position of the vertical line shown on the left.