Influence of accommodation on the viewing of an optical illusion

This study demonstrates the role of microfluctuations of accommodation in the viewing of the concentric ring illusion. Four experiments were carried out. Experiment I consisted of changing the distance between the illusion and the eyes but retaining visual angle, luminance and pupil size constant. In Experiment II, the accommodation of the eyes is paralysed by a cycloplegic. In Experiment III, the illusion is shown to a monocular aphakic and in Experiment IV, the exposure time is varied between 1/100 and 5 sec. Furthermore, a series of observations compared the concentric ring illusion seen with both eyes simultaneously. The evidence provided by the results of these experiments plus others discussed provide evidence that the concentric ring illusion is caused by the microfluctuations of accommodation.