Earlier work from this laboratory established that cylovergence is induced more effectively by vertical shear disparity than by horizontal shear disparity in a large textured surface. We predicted that vertical shear disparity confined to stimuli along the horizontal meridian would evoke more cyclovergence than stimuli confined to the periphery. That is, shear disparity in the periphery can arise from surface inclination, while disparity along the central meridian arises only from torsional misalignment of the eyes. Binocular dichoptic stimuli were rotated in counterphase through 5° peak-to-peak disparity at 0.1 Hz and presented in a mirror stereoscope. The stimuli were 70° long randomly spaced lines that (1) filled a 70° diameter circle, (2) were confined to a horizontal band 7° wide, (3) filled the 70° circle but with the central horizontal band blank. We used scleral search coils to measure cyclovergence of three subjects as they fixated at the center of planar stimuli. As predicted, the mean gain of cyclovergence was significantly higher (0.23) for the central band than for the display with the central band blank (0.12). However, the gain for the full 70° display was higher (0.36) than that for the central band. We conclude that stimuli along the central horizontal meridian provide a stronger stimulus for cyclovergence than do stimuli outside the central meridian. However, increasing the total area of the stimulus also increases the gain of cyclovergence.Acknowledgements: Supported by grants from the National Science and Engineering Council of Canada and the Canadian Institutes of Health Research.