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要旨

In line with the “feature similarity gain” model we observed a global enhancement of steady state visual evoked potential (SSVEP) amplitudes for flickering random dot kinematograms (RDKs) that shared the to‐be‐attended color regardless of the to‐be‐attended location. In a second study we instructed subjects to shift attention from one color to another in two superimposed centrally presented RDKs. We found an enhancement of the attended and a delayed suppression of the unattended color, suggesting two temporarily well separated neural mechanisms. The critical question: Is our observed time course restricted to the attended location or globally as well? We presented two additional and task irrelevant RDKs that flanked the, as in our previous study, centrally presented RDKs. The peripheral RDKs were of one color of the central RDKs, respectively, at which subjects performed a target discrimination task. As in our previous study we found a global enhancement of the signal elicited by the attended color, irrespective of the focus of spatial attention. The delayed suppression of the unattended color was limited to the centrally presented, superimposed RDKs and was not observed at the peripheral, spatially separated stimuli. The crucial deviation from a generalized biphasic mechanism at spatially separated RDKs either suggests an important role of the focus of spatial attention or the need for highly overlapping stimuli directly competing for processing resources.