Abstract
In experiment 1, a digit (or oriented bar) was defined by dark grey dots embedded in surrounding light dots for the left eye, and by light grey dots embedded in surrounding dark dots for the right eye. With one eye open, the digits (or oriented bar) were clearly visible, but with both eyes open the light and dark dots fused binocularly into medium grey making the digit (or bar) no longer visible. A similar result was found in experiment 2 when a digit was defined by greenish dots embedded in reddish dots for the left eye, and by reddish dots embedded in greenish dots for the right eye (somewhat like an Isihara colour plate). In a third experiment, yellow dots defined the same digit to both eyes, but the surrounding dots were reddish to one eye and greenish to the other. With one eye open, the digits used in experiments 2 and 3 were clearly readable, but with both eyes open the red and green dots fused binocularly into yellow making the digit no longer visible. In a fourth experiment, the dots defining the digit moved upwards and the surround dots moved downwards, for one eye, while the digit dots moved downwards and the surround dots moved upwards, for the other eye. Common fate made the digits clearly visible with one eye open, but motion averaging between the eyes made the digits invisible when both eyes were open. These results show that luminance, colour and motion information that is clearly present in the visual system at an early stage can be discarded or suppressed by binocular fusion, making two eyes worse than one.