The angular function of orientation illusions induced by projected images of tilted real object scenes.

Tilt aftereffects induced by line gratings are maximal when the test and inducing stimuli have an angular separation of 10 degrees-15 degrees. Similar effects induced by prismatically tilted real-object scenes have been found to increase monotonically with scene tilt. The difference between these two angular functions of aftereffect (that induced by gratings and that induced by real objects) has been attributed to the 'meaning' inherent in the real-object scenes. The preliminary experiments described here suggest that tilt aftereffects and illusions induced by projected slides of tilted real-object scenes have angular functions similar to that induced by a line grating. Hence, the monotonically increasing angular function obtained in the prism studies is not necessarily determined by the use of real-object scenes.