The perception of object motion during smooth pursuit eye movements: adjacency is not a factor contributing to the Filehne illusion.

During smooth pursuit eye movement performance often an illusory motion of background objects is perceived. This so called Filehne illusion has been quantified and explored by Mack and Herman [Q. J.exp. Psychol. 25, 71-84 (1973); Vision Res. 18, 55-62 (1978)]. According to them two independent factors contribute to the Filehne illusion: (1) a subject relative factor, viz. the underregistration of pursuit eye movements by the perceptual system, and (2) an object relative factor, viz. adjacency of the pursued fixation point and the background stimulus. The evidence of the present experiment supports the former but rejects the latter as a contributing factor. Instead of the concept of adjacency, an alternative theoretical extension of the subject relative factor is offered.