Studies of Spectral Sensitivity as Measured by a Procedure of Flicker Threshold

Subjects adjusted the radiance of monochromatic stimuli, modulated at constant frequencies, to produce just‐detectable flicker. Experiment I showed that spectral sensitivity determined at frequencies 20–35 Hz matches CIE photopic luminous efficiency: higher frequencies (40–45 Hz) yielded reduced sensitivity to long wavelengths. Experiment II showed that increasing intensity alone narrows spectral sensitivity, whereas increasing frequency broadens it. Experiment III isolated three modulation‐sensitive mechanisms by chromatic adaptation: these mechanisms have spectral sensitivities similar to Stiles' π1 π4. and π5.