Abstract
Under natural viewing conditions binocular disparity can provide metric depth information; many of the monocular depth cues, such as occlusion, provide depth order only. Nonetheless, when put in conflict there is evidence that occlusion can influence the direction and magnitude of perceived depth from stereopsis. Here we explored the integration of depth information from occlusion and binocular disparity in complex real-world environments using a depth matching paradigm. The virtual stimulus was a green letter ‘A’ presented using a Microsoft HoloLens augmented reality (AR) display and superimposed on a real frontoparallel surface at 1.2 m. The letter was placed at one of eight positions – between 0.9 and 1.6 m, including the surface location. Observers matched the distance of a probe to the perceived distance of the letter by moving it with a sliding pole. For comparison, observers performed the same task without the physical surface. Our results show that when the surface was absent or the letter was rendered in front of the surface the letter was accurately localized. However, when the letter was rendered beyond the surface, observers progressively underestimated the letter’s distance, even though the relative disparity between the probe and the target should have been equally informative at all locations. This pattern of results suggests that 1) observers are unable to ignore conflicts between occlusion and binocular disparity and 2) the occlusion conflict biases the perceived position of the target in the direction of the occluder. Our results are well modelled using a Bayesian ideal observer with an asymmetric likelihood for an occlusion cue representing letter positions in front of vs beyond the surface. In addition to providing insight into the integration of ordinal and metric depth information, these results speak to the impact of such errors in AR on user interactions.