Vergence accuracy in an autostereoscopic display
When fixating an object, observers typically under or over-converge by a small amount, a phenomenon known as "fixation disparity". Fixation disparity is typically measured with physical fixation targets and dichotically presented nonius lines. Here we made fixation disparity measurements with an autostereoscopic display, varying the retinal eccentricity and disparity of the fixation targets. Measurements were made in a group of four practiced observers and in a group of thirteen experimentally naive observers. Fixation disparities with a zero-disparity target were in the direction of fixation behind the plane of the screen and the magnitude of the fixation disparity grew with the eccentricity of the fixation targets (1-5 deg in the practiced observers and 1 - 10 deg in the naive observers). Fixation disparity also increased with increasing disparity of the targets, especially when they were presented at crossed disparities. Fixation disparities were larger overall for naive observers who additionally did not converge in front of the screen when vergence demand was created by crossed disparity fusion locks presented at 5 and 10 deg eccentricities.