Neural binocular summation and the effect of defocus on the pattern electroretinogram and visual evoked potentials for different pupil sizes.

Smaller pupil size and levels of defocus produced greater changes in cortical activity as evidenced by both the PERG and VEP. Considering these changes and the obtained positive BS, the mechanism could be initiated as early as the retinal processing stage, then being modulated and enhanced along the visual pathway and within the visual cortex.