THE DYNAMICS OF VERTICAL VERGENCE

We measured the gain and phase of vertical vergence in response to dis junctive vertical oscillations of dichoptic textured displays. The tex ture elements were m-scaled to equate visibility over the area of the display and were aperiodic and varied in shape so as to avoid spurious binocular matches. The display subtended 65 degrees and oscillated th rough peak-to-peak amplitudes from 18 are min to 4 degrees at frequenc ies from 0.05 to 2 Hz - larger ranges than used in previous investigat ions. The gain of vergence was near 1 when the stimulus oscillated at 18 are min at a frequency of 0.1 Hz or less. As the amplitude of stimu lus oscillation increased from 18 are min to 4 degrees, vergence gain decreased at all frequencies, which is evidence of a nonlinearity. Gai n declined with increasing stimulus frequency but was still about 0.5 at 2 Hz for an amplitude of 18 are min. Phase lag increased from less than 10 degrees at a stimulus frequency of 0.05 Hz to between 100 degr ees and 145 degrees at 2 Hz. Overall, the dynamics of vertical vergenc e resemble the dynamics of horizontal vergence and cyclovergence.