Contourless stimuli produce binocular brightness summation.

Absolute magnitude estimates by 16 observers reveal that complete binocular brightness summation occurs for flashed Ganzfeld conditions. In other words, the view using both eyes appears twice as bright as with one. However, using the same technique, but with 2 degrees fields, no such summation is found. In addition to showing that, on the average, human observers can act as photometers, the results suggest that either complete summation or averaging of the monocular brightness can occur, depending upon the presence of contours.