If, after being in the dark for many minutes, one views an extended surface under dim (scotopic) illumination, one fails to see any hint of the dark spot at the center of gaze that might be expected from the absence of rods in the fovea. Here we report that, if the surface is suddenly completely darkened, one sees for a few seconds a relatively bright spot, about 2 deg in size, at the point of fixation. If the surface is now restored to its original brightness, a dark spot of similar size appears where one fixates, that again lasts for several seconds. All this can be observed with no elaborate apparatus.
Get full access to this article
View all access options for this article.
References
1.
DitchburnR WGinsborgB L, 1952Nature17036–37
2.
ExnerS, 1868Zentralblatt für die medizinischen Wissenschaften6594–596
3.
von HelmholtzH, 1867/1962Treatise on Physiological Opticsvolume 2 (New York: Dover, 1962); English translation by SouthallJ P C for the Optical Society of America (1925) from the 3rd German edition of Handbuch der physiologischen Optik (first published in 1867, Leipzig: Voss, 3rd edition 1911, Hamburg: Voss) page 304
