Neurobiology of the Eye
Adaptation of the visual system to vertical shifts in retinal image position
When the spectacles are lifted on one side only, the prismatic effect of the lenses generates a vertical displacement of the two retinal images with respect to each other. This is disturbing since it causes diplopia (double images). However, in a few seconds to minutes, the images are fused, at least for disparities of up to about 3 prism diopters. We were interested to know whether the fusion occurs by changed vertical elevation of the eyes with respect to each other, or by shifting cortical maps. Therefore, an optical technique (binocular gaze tracker, see picture binoc1) and a psychophysical technique (see picture binoc2), designed to measure subjective elevation were combined.
At present, it looks like as if vertical disparities are rapidly compensated by non-conjugate vertical eye movements. When the disparites persists, the eyes return to their normal, symmetrical elevation but a prolonged shift can be detected in the psychophysical test.
Future project of Felix Maier (PhD): Center of integrative neuroscience (CIN), Tuebingen.