Control of oculomotor reflexes: independent effects of strategic and automatic preparation.
The reduction in saccade latency when the fixation point is removed (fixation offset effect-FOE) reflects the degree to which fixation neurons are under influence by a stimulus at fixation. Strategic manipulations of oculomotor readiness that bring these neurons under endogenous control reduce the magnitude of the FOE. Using an aging foreperiod paradigm, and the FOE as a marker for cortical control of reflexive fixation, we showed that, for both prosaccades and antisaccades, increasing preparation across the foreperiod reduced both saccade latency and the FOE. Consistent with Los's trace conditioning account, these effects reflected greater preparation for trials when the current short foreperiod was preceded by a trial with a short foreperiod. The FOE was also smaller for antisaccades than for prosaccades demonstrating strategic modulation. However, the effects of trace conditioning were comparable in the two tasks, demonstrating that strategic and unconscious priming effects both independently modulate the control of ocular fixation.