Peripheral Contrast Thresholds of the Human Eye

Experimental results concerning the behavior of the contrast threshold are given as obtained from about 100,000 responses of the same subject.The circular test spot of size d between 6.6′ and 8° was projected 7° nasal from the fovea. Green light was used for background and test spot. The stimulus exposure t was varied between 0.02 and 1 second.So long as d and t are small, the behavior of ΔB/B agrees with the explanation of de Vries: ΔB~B12. The dependence of the sensitivity of the eye on B is calculated from the precise shape of the curve for ΔB as a function of B for these combinations of d and t. The result does not contradict direct measurements of the sensitivity.