Temporal Summation during Dark Adaptation*

Abstract

The change of critical duration and of the form of the function relating threshold energy to stimulus duration was determined during the first 22 s of dark adaptation following light adaptation to several luminances. For all adapting luminances tested, the critical duration increased during dark adaptation from the value obtained for the increment threshold. As adapting luminance decreased or time in the dark increased, the form of the summation function changed, so that the transition from complete temporal summation to no summation became less abrupt. The data show departures from the equivalent-background analysis of dark adaptation. A filter model relating threshold energy and time constant under varying adaptation conditions provides a general, but not precise, description of the data. The change of temporal summation during dark adaptation is similar to that found for decreased size of test field, decreased wavelength of test field, and decreased background luminance.