Inhibition of return in pro- and anti-localization tasks with mixed and blocked designs

There are thought to be two forms of inhibition of return (IOR) depending on whether the oculomotor system is activated or suppressed. When saccades are allowed, output-based IOR is generated, whereas input-based IOR arises when saccades are forbidden. In a series of six experiments, we mixed or blocked pro- and anti-localization trials in order to investigate whether cueing effects would follow the same pattern as those observed with more traditional peripheral onsets and central arrows. In all experiments, an uninformative cue was displayed, followed by a cue-back stimulus that was either red or green. Green cue-backs indicated that pro-localization responses were to be made to the upcoming targets, whereas red called for anti-localization (respond opposite the targets). In the first experiment, subjects did not make any saccades, whereas saccades were made to cues in Experiment 2, and to targets in Experiment 3. Experiments 1 to 3 used a mixed design, with intermixed pro- and anti-localization responses, whereas Experiments 4 to 6 repeated the same experiments with a blocked design. We predicted that prolocalization trials would show the same pattern of effects as previously observed (IOR in all experiments), whereas anti-localization trials would result in IOR when the oculomotor system was activated and no effect when suppressed. However, our results showed that for pro-localization, IOR was only observed when saccades were made to the targets in a mixed design, although IOR was elicited in all three blocked experiments. For the anti-localization condition, IOR was only observed with saccadic responses in the mixed design, whereas facilitation was observed with manual responses in the blocked design. Challenging the influential two forms theory of IOR, this suggests a dissociation in cueing effects depending on response modality when a complex, mixed design is used.