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why is the visual field not circular

We investigated the effect of artificial parafoveal scotomata on the multifocal electroretinogram (M-ERG). M-ERGs were recorded from normal subjects using a monitor with several different sizes of black paper attached. A lower response density area around the 10 to 15 degree parafoveal region was not recognized for scotomata up to 3 degrees but was observed in scotomata above 5 degrees (visual angle) in the field topography of M-ERG. The shape of the scotomata was not circular but somewhat oval.

The results from two cases of parafoveal retinal degeneration accorded well with this basic study.
We determined the relative effectiveness of different areas of the visual field in determining the perceptual upright. The perceptual upright was measured using the character вpв, the identity of which depended on its perceived orientation (the Oriented Character Recognition Test).

The visual field was divided into left and right, upper and lower, and central and peripheral halves, with different backgrounds presented in each area. The left and right visual fields contributed equally to the perceptual upright while the lower visual field demonstrated a larger effect on the perceptual upright as compared to the upper visual field.

The central and peripheral visual fields interacted with one another in a complex manner, although a separate experiment suggested that the peripheral visual field did not alter the perceived orientation of the central field.

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