Figure 1.

Custom goggles. (A) Custom control goggles were each constructed from clear safety goggles, which were covered with black electrical tape on the front and sides to restrict the field of view to match that of the prism goggles. (B) Prism goggles were each constructed using two right-angle prisms custom cut and polished from a clear acrylic cube (Tap Plastics, San Jose, CA). Frames were designed from a welder's mask base and heavy-duty black plastic. Goggles rested against each subject's forehead and nasion, held in place with adjustable elastic bands over the head (white straps). Black felt at the temples and within the base of the welder's mask prevented normal visual input from the periphery. Maximum field of view through the goggles was approximately 45°–55° vertically by 60°–77° horizontally. Prism position was manually adjusted for each subject to provide the maximum range of binocular vision. Subjects had normal depth perception from approximately 40 cm to infinity. (C) Prism dimensions (left) and close-up of one right-angle prism (right). (D–F) Cartoon Illustrations of Visual Alterations: (D) Normal, completely unaltered view of the world. (E) The view through the control goggles, which restrict the field of view to the same extent as the prism goggles, but have no other visual alterations. (C) The view through the prism goggles with left–right-reversed visual input and restricted field of view.