EYE TORSION ASSOCIATED WITH DISPARITY-INDUCED VERTICAL VERGENCE IN HUMANS

Recently, Enright described an unexpected association between disparit y-induced vertical vergence and cycloversion (conjugate eye torsion) [ Enright (1992) Vision Research, 415, 279]. The present experiments wer e performed to verify these findings and investigate the nature of thi s association. We presented subjects with a dichoptic image of concent ric circles in which a step in vertical disparity of 1 deg was introdu ced. After 4 sec the disparity was eliminated. Eye movements were meas ured with scleral coils. We confirmed Enright's findings in that a lef t-over right vertical vergence was associated with levo-cycloversion ( upper poles towards left shoulder) and vice versa. The size of the cyc loversion and the vertical vergence were in the same range. In additio n we found that part of the cycloversion response was in the form of a torsional nystagmus and that the relative contribution of the left an d right eyes was independent of the horizontal gaze angle. These addit ional findings are in conflict with the hypothesis, offered by Enright , that the association is caused by a bilateral activity of the superi or oblique muscles.