The role of attention in the facilitation effect and another "inhibition of return".

The present study investigated how anticipation of a target's appearance affects human attention to gaze cues provided by a schematic face. Subjects in a 'catch' group received a high number of 'catch' trials, in which no target stimulus appeared. Subjects in the control group did not receive any catch trials. As in previous studies, both groups showed a facilitation effect to the cued location during shorter stimulus onset asynchrony (SOA). In both groups, an analysis of eye movements confirmed that subjects' eyes remained on the fixation point, ruling out the possibility that the facilitation effect was due to shifting eye movements (saccades) as opposed to a shift in covert attention. But while the control group's response time (RT) decreased as SOA increased, the catch group's RT had a U-shaped pattern and the facilitation effect to the cued location was reversed at the longest SOA (1005 ms). These results suggest that subjects in the catch group disengaged their attention during long SOAs because they expected the trial to be a catch trial. This disengagement of attention during long SOAs results in a delay before attention could be re-focused to the previous location regardless of the cue validity ["IOR (inhibition of return)"-like-phenomenon]. Unlike the conventional IOR, we suggest that this "IOR"-like phenomenon caused by an unpredictive central gaze cue is likely to be mediated by an endogenous mechanism.