Abstract

Measurements of absolute and contrast thresholds values 7° nasal from the fovea for 6500 and 5250A for line-shaped targets 2′ in width, length l between 2′–256′ and time of observation t between 0.02-1 seconds are presented.

The absolute thresholds agree with what was to be expected from the two-quanta theory, For l > 32′ for green flashes and for l > 8′ for red ones, ${\overline{N}}_{60\hspace{0.17em}\text{percent}}∾l^{\frac{1}{2}}$ and for t > 0.1 second, ${\overline{N}}_{60\hspace{0.17em}\text{percent}}∾t^{\frac{1}{2}}$. When t < 0.1 second or l < 32′ for green and l < 8′ for red light, Bunsen-Roscoe’s and Ricco’s law, respectively, is valid. Also, predictions for the behavior of the contrast thresholds for line-shaped sources are made which are also based on the quanta theories for these visual functions. The dependence of the contrast threshold ${〈\mathrm{\Delta }{\overline{N}}_{60\hspace{0.17em}\text{percent}}〉}_{\text{Av}}$ on l for large l for line-shaped targets is equal to the dependence of ${〈\mathrm{\Delta }{\overline{N}}_{60\hspace{0.17em}\text{percent}}〉}_{\text{Av}}$ on t and corresponds with the dependence of ${〈\mathrm{\Delta }{\overline{N}}_{60\hspace{0.17em}\text{percent}}〉}_{\text{Av}}$ on t and on the diameter d of circular flashes in the way predicted by theory.

© 1953 Optical Society of America

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