Threshold measurements of spectral sensitivity in a blue monocone monochromat.

Threshold measurements of spectral sensitivity were obtained from a blue monocone monochromat using a foveal fixation target. The dark-adapted spectral sensitivity function could be represented by the luminosity function of the rods (CIE C\) weighted by xanthophyll. With a 6.2 troland (id) background the spectral sensitivity function was identical to that of the blue cones (Stiles iri) for wavelengths between 395 and 505 nm. With a 0.4-td background, a double-peaked function was obtained, representing the complete linear summation of the V\ function and blue cones. It is suggested that the V>. function obtained with a foveal fixation target is determined by cones and not rods.