Binocular combination of contrast signals from orthogonal orientation channels.

In a series of psychophysical experiments, observers compared the apparent contrast of a dichoptic stimulus (contrast edges of orthogonal orientations in the two eyes) and a monocular stimulus ( a pie pattern in one eye and a blank field in the other eye). When the contrast of the dichoptic stimulus was low (2-3%) the two orthogonal edges were perceived as a stable pie pattern and its apparent contrast matched with that of a monocular pie pattern whose contrast was twice the contrast of the dichoptic stimulus. The dichoptic contrast gain (monocular/dichoptic contrast ratio) decreased with increasing dichoptic contrast. Although the observers showed an inability to discriminate the apparent contrasts of the dichoptic and the monocular pie patterns, they were able to tell which stimulus was the dichoptic one in a forced choice paradigm. A binocular contrast preservation model was proposed for binocular combination of contrast signals from orthogonal orientation channels.