Purpose. The purpose of this study was to examine in detail the binocular fixation top-view trajectories of saccade-vergence responses to asymmetrical targets, and to compare latency difference between saccade and vergence, under the free- and instrument-space viewing environments. Methods. Binocular eye movements were recorded using the infrared reflection technique in five visually-normal subjects. Responses were obtained for various asymmetrical target positions under both free- and instrument-space environments. Results. Four types of top-view trajectories that represented normal variations in saccade and vergence control were found: straight, overshoot, undershoot, and saccade-vergence. Also, it was found that under the instrument-space environmental there was a predominance of saccade-vergence trajectories and a scarcity of overshoot trajectories, whereas under the free-space environment, there was a predominance of overshoot trajectories, and a scarcity of saccade-vergence trajectories. Further, under the instrument-space environment, latency was significantly longer fur saccade than vergence (35.9 ± 15.7 msec; t = 5.1, degrees of freedom (df) = 4, P < 0.01), whereas under the free-space environment, there was no latency difference (- 10.5 ± 14.8 msec; t = -1.6, df = 4, P > 0.05). Conclusions. The differences in response profiles under the two viewing environments could be accounted for by differences in timing of saccade and vergence onset. Moreover, in contrast to some recent investigations that suggest higher center control of individual trajectories, which was dependent on the naturalistic scene, these trajectories could be accounted for by known neural and oculomotor mechanisms, with the higher centers using a priori information about spatial location of the target, to assist in the synchrony of saccade and vergence onset under the free-space environment.
All Science Journal Classification (ASJC) codes
- Sensory Systems
- Cellular and Molecular Neuroscience
- Eye movement trajectories
- Neural control