The Visibility of Black Objects Against an Illuminated Background

Measurements in terms of the total average number of quanta that must be intercepted from the background by a flash of various durations, shapes, and sizes in order to perceive a “negative” flash are presented for rod vision 7° nasal from the fovea.It proved that the results are fairly well described by quantatheoretical observations on the dependence of the absolute threshold on the visual angle of the test spot and the flashtime and such observations on the behavior of the contrast threshold.