Visual Sensitivities and Discriminations and Their Roles in Aviation.

A device has been developed (MIDAPT) that tests a subject's ability to track a target's motion in depth. The test has been encouragingly successful in predicting intersubject differences of pilots' flying performance in high-performance jet aircraft and in simulators. We report evidence that human observers' acute discrimination of differences in size (about 5%) and orientation (about 0.3 deg) is achieved by comparing the outputs of two or more neurons, each of which is sensitive to a rather broad range of sizes and orientations. We suggest that the human visual pathway contains size-opponent and orientation-opponent mechanisms, and that this can explain why subjects easily unconfound orientation, size and contrast in spite of the fact that the firing of cortical neurons is affected by all three parameters. We measured subjects' ability to detect a camouflaged object that was visible only when moving, and compared these data with similar measurements for conventional objects that were brighter than their surroundings. These findings may be relevant to low-level flight, for example in helicopters, where ground features may be virtually indistinguishable except when moving. Monocular ability to judge the direction of motion in depth was investigated by measuring the effect of adaptation to different directions of motion in depth for a target viewed with one eye. In contrast to binocular judgements of motion in depth, the results could be explained in terms of only two channels: one for frontal plane motion, and one for pure line-of-sight motion.