Anomalous loss in blue-green wavelength discrimination with very brief monochromatic stimuli presented to the normal human eye.

The wavelength-discrimination curve of the normal human eye shows minima in discrimination thresholds at about 490 and 580 nm for viewing times of 1 s or longer. A reduction in viewing time was found to yield non-uniform increases in discrimination thresholds in the blue-green region of the spectrum, and these findings were quantified in objective, two-interval, forced-choice discrimination measurements. Monochromatic stimuli were presented foveally in a circular, horizontally oriented, bipartite field of 100 Td and angular subtense 2 degrees. When viewing time was decreased to 3 ms there was a sharp increase in discrimination threshold over 490-520 nm, maximizing near 500 nm. In this region, the fields appeared markedly desaturated. The loss in discrimination was distinct from that exhibited by tritanopes, and a control experiment showed that the effect was not attributable to the reduced energy of the short flash.