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

Inhibition of return (IOR) is a response delay when the target is preceded by an irrelevant stimulus (cue) at the same location. In a previous study, we investigated the separate and joint effects on IOR of cue onset and offset. IOR was much greater when cue onset was followed by cue offset (on-off cue) than when the cue 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 two cue events. Three experiments were conducted. In Experiment 1 we replicated, 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 Experiments 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 was compared with an off-off cue. Results showed that the magnitude of IOR did not simply depend on the number of cue events occurring before the target. IOR was greater with two different events than with two identical events and greater when was preceded by an off-event than an on-event. Therefore, IOR was greatest with an on-off cue, which likely also benefited from a gap effect. Possible mechanisms underlying IOR were discussed. Received: 31 March 1999 / Accepted: 23 July 1999