Abstract

We compared the amount of binocular summation, defined in the usual way by the monocular/binocular threshold ratio, with the threshold effect of adapting luminance. The luminance effect obeyed Weber’s law: The slope of the threshold vs intensity function was unity for monocular as well as binocular thresholds; it was the same among all eyes and observers. The amount of binocular summation was independent of adapting luminance, but it varied among the eyes of the six normal observers between a factor of 1 (no summation) and a factor of 2 (full summation). Except in one observer, monocular thresholds remained about the same when the nontest eye was occluded, as when both eyes viewed binocularly fused backgrounds of equal luminance. Global stereoscopic relief imposed on the background had no effect on thresholds or on the amount of binocular summation. No single rule common to all observers would predict binocular performance from monocular performances alone. At least two binocular channels must contribute to the net response at the increment threshold.

© 1986 Optical Society of America