CYCLOVERGENCE - A COMPARISON OF OBJECTIVE AND PSYCHOPHYSICAL MEASUREMENTS

Several psychophysical procedures have been used to measure cycloverge nce but none has been adequately validated with respect to an objectiv e measure. Scleral search coils were used to measure cyclovergence ind uced by dichoptic textured patterns which cyclorotated in antiphase th rough 6-degrees at frequencies between 0.05 and 2 Hz. In one psychophy sical procedure subjects nulled the apparent oscillatory motion of rad ial nonius lines superimposed on a small black disc at the center of a large cyclorotating display. In the second, subjects nulled the appar ent inclination in depth of a vertical line displayed in the same way. The amplitude of cyclovergence measured objectively and the magnitude of oscillation of the nonius lines were similar at low stimulus frequ encies. At higher frequencies of cyclorotation, both amplitudes declin ed but the nonius amplitude exceeded that of cyclovergence. The appare nt inclination of the vertical test line, as indicated by the nulling procedure, also declined with increasing frequency of cyclorotation, b ut not at the same rate. At low frequencies, the apparent inclination of the test line was greater than that corresponding to the cyclodispa rity induced into the line and almost as great as that corresponding t o the relative disparity between the oscillating pattern and the line. The implications of these results for measuring cyclovergence and for an understanding of stimuli driving cyclovergence and perceived incli nation in depth are discussed.