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Perception of distance in a binocular helmet-mounted display: data from helicopter in-flight video tapes

An experiment was performed to determine if the geometrical arrangement of sensors delivering images from the environment, could influence distance perception is a binocular helmet-mounted display (HMD). A pair of cameras were settled in the front part of a PUMA helicopter. Video tapes were recorded during low altitude flights. Six camera settings were tested resulting from 3 magnitudes of the separation between the sensors, and 2 arrangements of the optical axes of the cameras: parallel or convergent. Displaying the image of a single camera on both optics of the HMD provided an additional condition which served as a reference free of binocular depth cue. The video tapes were displayed on a 40 degree full overlap HMD. Eleven helicopter pilots ran the experiment. Objective comparison of the sensor configurations was based on distance or height estimation following a bi-section paradigm. As a subjective comparison, the pilots classified the sensor configurations according to the quality of 3D perception of the environment. Objective data show that flight safety is increased when the separation between the senor is larger in both convergent and parallel settings. Subjectively, the pilots preferred the wide separation and convergent setting of the cameras.