Quantitative assessment of divergence eye movements to ramp stimuli

Vergence eye movements are the inward (convergence) or outward (divergence) turning of the eyes which allows humans to view images in depth. This study compares converging responses where the stimuli are approaching the subject to diverging responses where the stimuli are moving away from the subject from 10, 6, and 2 degree/s ramp stimuli. Results show that similar to convergence, divergence may be governed by a two component control system consisting of a transient and sustained component. However, the dynamics of divergence shows a dependency on initial stimulus position which is not apparent for convergent responses. This study also shows that for fast drawing divergent responses, high-velocity components were present lending further evidence that a transient component similar in form and function to that found in convergence also exists for divergence. Responses to slow moving responses exhibit smoother tracking where the dynamics of the movement were more uniform throughout the range of the visual field. This implies that the transient component is more prominent in faster responses thus showing a strong dependency on initial stimulus position. With slower moving responses, the transient component did not dominant the movement leading to more homogeneous dynamic responses where a dependency on initial stimulus position was not as apparent.