Effects of Transient Weightlessness on Brightness Discrimination.

Contrast thresholds of six semisupine, visually adapted subjects were obtained under short (10-14 sec.) periods of weightlessness and under 1 G control conditions. The target, viewed binocularly, subtended 1.5 ~ and the background 2.6*. Three background luminance levels were used: 0.03, 0.28 and 30.0 ft-L. The contrast required to detect the target was found to be slightly, but consistently, lower under the weightless condition than under the control 1-G condition. Under the weightless condition the contrast required to detect the target averaged 12.56 per cent at 0.03 ft.-L background luminance, 6.49 per cent at 0.28 ft.-L background luminance and 3.99 per cent at 30.0 ft.-L background luminance. The corresponding contrasts required under the control I-G condition averaged 15.14, 7.05 and 4.45 per cent respectively.