Comparison of disparity vergence system responses to predictable and non-predictable stimulations

Prediction is an important component of the neural strategy used to guide the human visuomotor system. When applicable, prediction significantly enhances the performance of oculomotor control. Previous research has shown that the use of prediction will decrease the latency of movement onset as seen in saccadic as well as disparity convergent eye movements. Prediction also decreases tracking error in the smooth pursuit system. This study analyzed the latency and the magnitude of peak acceleration of convergent and divergent disparity eye movements when the stimuli could, and could not, be predicted. Non-predictive disparity vergence four-degree step responses were presented to a subject after a random delay of one half to two seconds. To further avoid prediction, various types of stimuli were presented to a subject randomly. Predictive symmetric disparity vergence four-degree step responses were presented using a periodic square wave with a frequency of 0.5 Hz for 20 seconds. Eye movements were recorded using an infrared limbus detection system. Results show that the response timing index - the time from stimulus onset to peak velocity - decreases and movements can even occur before stimulus onset when prediction is evoked. The magnitude of peak acceleration for predictive movements in both convergence and divergence shows a statistically significant increase compared to non-predictive movements. Furthermore, two distinct behaviors for predictive convergent responses were observed, although with predictive divergent responses we observed only a single behavior. Through the neural mechanism of prediction, the performance of convergent and divergent eye movements was improved as seen by the decrease in eye movement latency and the increase in the magnitude of the movement's peak acceleration.