In this paper, experiments are described in which brightness constancy
was studied in a Ganzfeld environment. Luminance variation by means o
f neutral density filters was applied to stimuli consisting of a Ganzf
eld with superimposed disks. To this end, a special-purpose apparatus
was constructed. Sequential dichoptical brightness matches with a refe
rence stimulus were carried out for the disks as well as the homogeneo
us surround. The results of these measurements indicate that (1) besid
es a clear tendency toward brightness constancy, small but systematic
effects of the average luminance level are present and (2) the brightn
ess of the Ganzfeld is hardly affected by the presence of the disks. F
inally, it is shown that the experimental results can be modeled adequ
ately in terms of a concept that involves an accumulation of contrast
information.