Abstract
[Purpose] By taking advantage of binocular rivalry, different perceptual changes can be produced with a physically identical stimulus sequence. When different brightness changes were produced using this technique, the pupillary response exhibited percept-related changes (Kimura et al., ECVP2009). This study investigated the generality of this finding using various stimulus sequences of white and black disks. [Methods] At the start of each trial, the observer dichoptically viewed white (8 cd/m2) and black (2 cd/m2) disks presented on a gray background (4 cd/m2) and pressed a key when one of the disks became exclusively dominant. The key press initiated a stimulus change to one of the followings after a short break; the same dichoptic white and black disks (WB), binocular white disks (WW), binocular black disks (BB), or dichoptic black and white disks (eye switching, BW). For example, when the initial dominant percept was black, the WW condition produced a black-to-white perceptual change. However, the same WW condition produced a white-to-white change when the initial percept was white. [Results and Discussion] The percept-related change in the pupillary response was consistently found with different stimulus sequences; larger pupillary constrictions were evoked when apparent brightness increased more with a stimulus change. In the BW condition, a large contrast increment produced by the black-to-white stimulus change in one eye seemed to have made the white disk perceptually dominant regardless of the initial dominant percept. In the WB condition, an individual difference in the perceptual change was found when the initial percept was black. However, even with these nonsystematic variations in percept, the pupillary constriction amplitude changed consistently with the perceptual change. These findings suggest that, although the pupillary light reflex is believed to be a primitive reflex and mainly mediated by subcortical pathways, it also reflects neural activities correlated with perceptual changes.