Neural correlates of size illusions: an event-related potential study.

The aim of this study was to investigate the neural correlates of size illusions. Participants were presented with a sphere of a fixed angular size positioned (i) at either a far or close position within a three-dimensional virtual scene or (ii) at either an upper or lower screen position on a plain gray background. The visual-evoked potentials were recorded while participants were required to fixate on and attend to the sphere. The results showed that the amplitude of visual P2 component was affected by sphere position in the three-dimensional scene condition only, suggesting that the activity level of the primary visual cortex was modulated by the size illusion at later stages of visual processing.