Using a testfield subtending a visual angle of 5 degrees, dark adaptation functions were obtained with six test-exposures (1.0, 0.5, 0.1, 0.04, 0.02, and 0.01 sec) both from the central retina, and from the temporal parafovea. The functions for both retinal locations were found to vary systematically in relation to duration of testflash. With increasing test-exposure time, the final cone levels as well as the final rod levels are at lower threshold brightnesses. The sensitivity for a given test-exposure time is greater in the central retina than in the parafovea for the photopic range of vision, whereas the sensitivity for the scotopic.range is greater in the parafovea than in the central retina.
ERNST WOLF and MICHAEL J. ZIGLER, "Dark Adaptation Level and Duration of Testflash," J. Opt. Soc. Am. 41, 130-131 (1951)