Cross fuse lower image (X) or uncross fuse upper image (U). You will see a “phantom” rectangle out in front. It accounts for the absence of the middle parts of the lines. Its apparent position in depth is consistent with “hiding” the middle of the right line for the left eye and vice versa.

• Gillam, B., & Nakayama, K. (1999). Quantitative depth for a phantom surface can be based on cyclopean occlusion cues alone. Vision Research, 39, 109-112.