Fig. 5.

Results of Experiment 2 in which observers matched the orientation of the virtual line joining the two intersections in as Poggendorff figure. The matching stimulus was a circular Gabor patch containing a 3.75 c/deg grating that could be rotated by the observer in 1° steps until it appeared to match the orientation of the virtual line. The left hand panel shows the mean error made in the settings by three subjects (SB, TM, MM), where the error is defined as the shift towards the vertical orientation. The error bars represent standard deviations of the subject’s scores (note: not standard errors). The right hand panels shows these errors converted into errors in the Poggendorff direction (black lines), corrected for the Zehender bias by the method described in the text. The red lines show the Zehender bias towards the vertical.