Replication of the Lansford-Baker phenomenon confirmed that light adaptation of one eye in a particular way can subsequently lower thresholds during dark adaptation of the other eye. Pressureblinding the non-test eye when dark adapted lowered thresholds in the test eye by the same amount, but pressure-blinding the non-test eye when light adapted had no noticeable effect on the test eye. It follows that a dark adapted eye sends signals to the brain that interfere with detection of signals elicited from the test eye by weak stimuli. The evidence favours interpretation in terms of binocular rivalry rather than ordinary discrimination of signal from noise. © 1976.