FIXATION POINT OFFSETS FACILITATE ENDOGENOUS SACCADES

Subjects produced saccades to continuously visible targets that were s ignaled by the pitch, not the location, of an auditory signal. Such en dogenous saccades were initiated more quickly when the visual fixation point disappeared 200 msec before the signal (thus producing a ''gap' '), even though the alerting benefits of such a warning were eliminate d by an earlier warning tone. The presence of the gap effect under the se circumstances shows that the effect is more general than was previo usly believed: Visual fixation point offsets facilitate saccades by af fecting oculomotor processes related to both visually elicited (exogen ous) and centrally produced (endogenous) saccades. In addition, the ma gnitude of the gap effect for endogenous saccades was significantly sm aller than that for exogenous saccades, suggesting that at least some of the effect arises in relatively early processes, such as those invo lved in the processing of sensory signals, and not exclusively in late r processes, such as those involved in the preparation and production of saccades.