Abstract
In visual search, the presence of a salient but task-irrelevant distractor hampers target selection, slowing down performance. The dorsal frontoparietal network, including the Frontal Eye Field (FEF) and the Intraparietal Sulcus (IPS), plays a pivotal role in dealing with the interference engendered by a salient distractor. A recent study used repetitive Transcranial Magnetic Stimulation (rTMS) to assess the causal role of FEF and IPS in distractor filtering, showing that the stimulation of right (but not left) FEF reduced the behavioural cost elicited by the distractor, whereas no effect was obtained with TMS over IPS. Here we used single pulse TMS (spTMS) to investigate the temporal dynamics of target selection and distractor filtering mechanisms within rFEF. In two experiments, we interfered with the function of rFEF at different time points after search array onset (Experiment 1: 0, 100 and 250 ms; Experiment 2: 100, 350 and 450 ms) during the execution of a visual search task. Participants were asked to discriminate the orientation of a target stimulus while ignoring a salient color distractor, present in half of the trials. In Experiment 1, TMS over rFEF did not produce any influence over the distractor cost, but prolonged RTs when the target was located in the hemifield contralateral to the stimulation site, irrespective of distractor presence/location. In Experiment 2, TMS increased RTs only in distractor-present trials, selectively when the distractor was located in the contralateral hemifield, irrespective of target location. These observations suggest a biphasic role of rFEF in visual search: in a relatively early time window, rFEF mediates target selection in the hemifield opposite to the stimulation site, while in a later window it mediates filtering of a distractor, again opposite to the stimulation site, in turn facilitating target selection.