Date of Award

Winter 1982

Project Type


Program or Major


Degree Name

Doctor of Philosophy


The change in brightness due to an increase in the size of a test stimulus is termed spatial (areal) summation. The aim of the present research is to quantify spatial summation effects for a large range of stimulus sizes at two suprathreshold luminance levels and two stimulus presentation methods (binocular and haploscopic). Two experiments were performed. In the first experiment, the brightness matching technique was employed and in the second experiment, a magnitude estimation task was utilized. Brightness was found to increase when stimulus area increased. This brightness change was greater when stimulus luminance was high, than when stimulus luminance was low. Method of stimulus presentation had no effect on apparent brightness. These results are compared to other findings reported in the literature.