Modulation of inhibition of return by type and number of dynamic changes of the cue

(IOR) is a response delay when the target is preceded by an irrelevant stim ulus (cue) at the same location. In a previous study, we investigated the s eparate and joint effects on IOR of cue onset and offset. IOR was much grea ter when cue onset was followed by cue offset (on-off cue) than when the cu e was a single event (on or off cues). The aim of the present study was to test whether the greater IOR with an on-off cue is due to the presence of t wo cue events. Three experiments were conducted. In Experiment 1 we replica ted, with a different delay between cue onset and offset, the finding that IOR is greater with an on-off cue than with a single cue event. In Experime nts 2 and 3, we used cues formed by two events. In Experiment 2, an on-off cue was compared with an off-on cue, whereas in Experiment 3 an on-on cue w as compared with an off-off cue. Results showed that the magnitude of IOR d id not simply depend on the number of cue events occurring before the targe t. IOR was greater with two different events than with two identical events and greater when Inhibition of return was preceded by an off-event than an on-event. Therefore, IOR was greatest with an on-off cue, which likely als o benefited from a gap effect. Possible mechanisms underlying IOR were disc ussed.