EEG alpha oscillations in the preparation for global and local processing predict behavioral performance

Visual attention can be directed either to the global features of a display or to the local elements that make up the display. We investigated whether oscillatory brain responses to globally or locally directed cue stimuli predict behavioral performance in subsequent target processing. Induced alpha band (8-12 Hz) amplitudes in the pre-stimulus interval were measured separately for the global and the local level, where individual trials were assigned to one of three groups according to the response speed towards incongruent stimuli. Fast responses to local features were associated with high alpha amplitudes in the right centro-parietal cortex, whereas fast responses to global forms were associated with high alpha in left centro-parietal cortex. For trials with slower responses, the pattern of hemispheric differences was diminished or even reversed. It is interpreted that the left and the right parietal cortex exert top-down control over hierarchical processing by inhibiting stimulus representations in one hemisphere.