[a] In the center of the visual field, corresponding to the center of the fovea of the retina, a very large number of neurons process information from a small region of the visual field.
If the same stimulus is seen in the periphery of the visual field (i.e. away from the center), it would be processed by a much smaller number of neurons.
When expressed in this way, the values of cortical magnification factor vary by a factor of approximately 30 – 90 between the foveal and peripheral representation of the primary visual cortex (V1), depending on how the estimate is obtained.
[4] Visual performance depends importantly on the amount of cortical tissue devoted to the task.
As an example, spatial resolution (i.e. visual acuity) is best in the center of the fovea and lowest in the far periphery.