Payne W H
Science. 1967 Jan 27;155(3761):481-2. doi: 10.1126/science.155.3761.481.
Reaction times to a dim photopic stimulus were measured on a circle about the fovea, 15 degrees from the line of direct vision. Large variations in reaction time were found on various half meridians and were interpreted as reflecting the distribution of retinal receptors.