Vergence eye movements Saccade-vergence interactions Noncomitant vertical phoria adaptation
Otolith-dependent adaptation of vertical skew Neurophysiology of binocular eye movements
Contact information:James S. Maxwell
School of optometry
360 minor hall
University of california
Berkeley, ca 94720-2020
Phone: (510) 642-7710
Fax: (510) 643-5109
Mechanisms of Vertical Phoria Adaptation Revealed by Time-Course and Two-Dimensional Spatiotopic Maps, James S. Maxwell and Clifton M. Schor, 1994.The spatial spread of short-term phoria adaptation was measured in response to either a single vertical disparity presented at a single eye position, or, vertical disparities of opposite sign presented at two different locations along either the primary vertical or horizontal meridians or along an oblique axis. The spread of adaptation to eye positions not specifically adapted was assessed by measuring phoria across a two-dimensional surface. The change in phoria was uniform across the field in response to a single disparity. With two disparities, adaptation conformed to the stimulus demand in the direction in which the disparity varied but was uniform in the orthogonal direction. The time course of the adaptation indicated the presence of two mechanisms, a global one which shifted the phoria uniformly across the field and a local one which selectively adjusted the phoria to the position-dependent demands of the disparity.
Adaptation of Vertical Eye Alignment in Relation to Head Tilt, James S. Maxwell and Clifton M. Schor, I996Binocular visual feedback is used to continually calibrate binocular eye alignment so that the retinal images of the two eyes remain in correspondence. Past experiments have shown that vertical eye alignment (measured as vertical phoria) can be altered by training to disparities that vary as a function of orbital eye position. The present experiments demonstrate that vertical eye alignment can also be trained to differ with head position when eye position (with respect to the orbit) is held constant. Changes in head position were about either an earth-vertical or earth-horizontal axis to distinguish otolith-ocular related adaptation from cervical-ocular related adaptation. Changes in head position were implemented by either by rotating the whole body (WB) or by rotating the head with the body stationary (HO). Following training, adaptation of eye alignment was observed in all cases of rotation about an earth-horizontal axis and for HO pitch rotations about an earth-vertical axis. The results illustrate the ability of the oculomotor system to compensate for imbalances in otolith-ocular pathways.
Head-position-dependent adaptation of nonconcomitant vertical skew, James S. Maxwell and Clifton M. Schor, 1997Vertical phoria can be trained to vary with either head position or orbital eye position. The present experiments show that subjects can simultaneously adapt their eye-position-specific (noncomitant) vertical phorias in different directions at different head positions. Eye-position-dependent and head-position-dependent adaptive pathways, therefore, are not independent. Rather, the adaptation of vertical skew takes into account both eye and head position. In additional experiments, the magnitude of the noncomitant adaptive response was shown to be related to otolith output, increasing with head tilt ipsilateral to the tilt position at which training was received and decreasing in the contralateral direction.
Dynamics and Efficacy of Saccade-Facilitated Vergence Eye Movements in Monkeys,J.S. Maxwell and W.M. King, 1992Macaque monkeys were trained to alternately fixate targets requiring different combinations of horizontal version and vergence. Eye movements were recorded binocularly with search coils. The peak vergence velocity for combined vergence-saccade eye movements reached higher velocities than for vergence movements alone and vergence speed increased in direct proportion to saccade amplitude. We determined, however, that most of the increase in speed was due to the addition of transient vergence movements that occur for all saccades, even those between targets at the same distance where no vergence is required. Even so, vergence speeds during combined vergence-saccades exceeded the speeds predicted by the linear addition of saccade-related vergence transients and pure vergence movements. The increased vergence speeds were behaviorally relevant in that vergence duration was decreased. A distinction was made between the intrasaccadic vergence that occurred during saccades and the intrasaccadic vergence that occurred because of saccades by calculating the amount of vergence that would have occurred during the duration of the saccade (based on the average speed of pure vergence movements of comparable size and assuming linear addition) and subtracting that from the actual vergence obtained. The difference was assumed to be the portion of vergence contributed by a saccade-related mechanism and not by the slow vergence controller.