Position constancy during pursuit eye movement: An investigation of the filehne illusion

Experiments were performed to investigate the Filehne illusion, the apparent movement of the background during pursuit eye movements. In a dark room subjects tracked a luminous target as it moved at 3°/s or 10.5/s in front of an illuminated background which was either stationary or moved at a fraction of the target speed in the same or opposite direction. Subjects reported whether the background appeared to move and the direction of the movement. Results reveal only a partial loss of position constancy for the background during tracking. The stationary background is perceived to move slightly in the direction opposite to that in which the tracked target is moving. These results seemed best described as an instance of perceptual underconstancy and led to the speculation that the source of the illusion is an underestimation of the rate of pursuit eye movements. An experimental test of this hypothesis which produced supporting evidence is reported.