A white-noise photostimulator by using a pulse frequency modulation method

Abstract

A photostimulator of which radiant power is controlled in the form of white-noise is described and examined in order to study the visual color system, and it has excellent linearity and spectral constancy. Glow modulator tubes (R1131C; Sylvania and L526; HTV) were examined for the purpose of being used for the light source. The spectral concentration of the tube was measured at different current levels of 10, 30 and 50 mA. It is shown that the spectral concentration was changed with the variation of the driving current. The current control method is usually used to control the radiant power, but had the above imperfection for the experiments of the color vision. Another method, the pulse frequency modulation (PFM) method was also tested. These two methods were compared at different levels of the radiant power for five colors. By the usage of the PFM method, linearity and spectral constancy were remarkably improved, and this method was used in a white-noise photostimulator. How the eye responds to the flickering light of the PFM method is explained, and an application to the study of the horizontal cell in the carp rentina is described.