Visual noise causes tunnel vision

Ss had quickly to detect similarities between two uppercase letters presented peripherally and one other central letter falling on the fovea. These three characters were so legible that this task was very easy when the three letters were flashed on by themselves. But the addition of extra letters to this display seriously impaired performance. The periphery of the retina could no longer accurately detect at a glance whether items were similar. Foveal performance was also affected to some extent by extra items in the periphery of the retina.