Contrast sensitivity functions measured during early dark adaptation

Abstract

Last year we reported measurements of contrast sensitivity functions (CSFs) during long-term dark adaptation and on steady backgrounds. The targets were "increment-Gabor" patches—the sum of a 2D Gaussian-damped sinewave and a simple 2D Gaussian of the same amplitude. The major finding was that the CSFs changed shape as a function of steady background luminance (as expected from previous studies) but did not change shape during long-term dark adaptation. This latter result supports the hypothesis that long-term adaptation is both local and multiplicative. The present study measured CSFs (1 to 15 c/deg) during short-term dark adaptation and on steady backgrounds. For the short-term adaptation conditions, the adapting background was presented with a duty cycle of 3% (9.7 s on and 0.3 s off), and the target was presented 175 ms after background offset. We found, in the short-term adaptation (and steady-background) conditions, that the CSFs became flatter as adapting illumination increased from 0 to 100,000 trolands. This implies that short-term dark adaptation cannot be simultaneously local and multiplicative.