Visual selection and the human frontal eye fields: effects of frontal transcranial magnetic stimulation on partial report analyzed by Bundesen's theory of visual attention

While the frontal eye fields (FEF) are traditionally associated with eye movements, recent work indicates possible roles in controlling selective visual processing. We applied 10 Hz bursts of transcranial magnetic stimulation (TMS) over left or right human FEF while subjects performed a partial-report task that allowed quantitative estimates of top-down control and other parameters affecting visual performance. Participants selectively reported digits in a relevant color (targets) but not those in an irrelevant color (nontargets) from a brief masked display. A target could appear alone or together with an accompanying item (nontarget or target) in the same or opposite hemifield. Targets were normally identified better when presented with a nontarget than with another target, indicating prioritization of task-relevant targets and thus top-down control. We found this usual pattern of results without TMS, and also with TMS over left FEF. However, during right FEF TMS, the detrimental impact of accompanying distractors increased. Formal analysis in terms of Bundesen's (1990) theory of visual attention confirmed that right FEF TMS diminished the top-down control parameter for both hemifields, indicating an FEF role in top-down selection even for targets defined by the nonspatial property of color. Direct comparison with our previous findings for parietal TMS (Hung et al., 2005) confirmed the distinct role of FEF in top-down control, plus right-hemisphere predominance for this in humans.