Inhibition of return in averaging saccades.

When subjects make a quick saccade to one of two stimuli that are presented closely and simultaneously in the peripheral visual field, their eyes often land at a midpoint somewhere between the stimuli (saccadic averaging). The present study investigates whether and how the inhibition-of-return phenomenon (IOR; slower reaction times for the previously attended locations) influences spatial parameters of averaging saccades. Subjects were asked to quickly move their eyes toward one of two stimuli that were presented closely and simultaneously. Most subjects showed a clear tendency toward saccadic averaging. When an uninformative cue was presented 600 ms before the two stimuli (long enough to produce IOR), saccadic averaging still occurred but the saccade landing locations were biased toward the uncued location. Thus, the present study demonstrates that the mechanisms responsible for IOR affect the metrics of averaging saccades and suggests that IOR can be manifested not only in the temporal aspects but also in the spatial aspects of oculomotor behaviors.