ABSTRACT
Until the mid-twentieth century, visual science laboratories used mainly circular dots and disks as stimuli, without the benefit of spatial frequency analysis. A 2°-disk, for example, was the standard tool for isolating the performance of the high resolution part of the retina known as the fovea centra/is. These circular targets were also used to study flicker fusion, contrast sensitivity, color perception, and every other kind of response that was measured in the laboratories of the day.
