Foveal threshold of one eye when illuminated by contralateral steady light.

The effect of luminance of the contralateral steady light upon the foveal threshold was examined in the situation where both test-field and contralateral background (or surround) appeared to be completely fused when both were exposed simultaneously. The relation between the test threshold (defined as log Lt/Lto) and the luminance of the contralateral background (or surround) (I) was expressed by log (Lt/Lto) = a(1 - e-b log I), where a and b are constants.