SIMULTANEOUS HAND TRACKING DOES NOT AFFECT HUMAN VERGENCE PURSUIT

In order to find out whether human vergence eye movements are influenc ed by simultaneous hand tracking movements, vergence was studied when sinusoidal (expressed in vergence angles) target movements were tracke d. The target motion was externally generated and the target actually moved in depth. Tracking was done by the eyes alone or by the eyes and hand together, in both light and dark viewing conditions. Our data sh ow that the target motion was tracked by the eyes with a short delay ( on average 48 ms), independent of the tracking condition. This suggest s that vergence modeling should include some predictive mechanism simi lar to that proposed for the smooth pursuit subsystem. Furthermore, in contrast to effects on smooth pursuit, simultaneous hand tracking mov ements did not influence vergence eye movements. From this, we argue t hat the balance between smooth pursuit and saccadic eye movements is a djustable and can be adapted to the requirements of different tasks.