[The mechanism of gain in scale of visual attention]

Objective. To compare the cortical mechanisms associated with the visual spatial attention directed by fixed location cues. Method. The subjects were 12 healthy right-handed young volunteers. The visual stimuli were presented with the sequence as: background-cue-target. The cue was a black circle varied in three different sizes randomly. The foci of the circles were always at the center of the screen. The task of the subjects was to search the target within the cue circle and discriminate its orientation. Electroencephalogram (EEG) was recorded from 128 scalp sites. Result. The reaction time (RT) to the targets in the same location shortened when the cue size enlarged. The target evoked P1 and N1 components were not affected by the attentive region size, while the amplitudes of the inferoposterior P2 and anterosuperior N2 enlarged when the attentive region size enlarged. Conclusion. 1) The P1 and N1 components under visual attention were related to the spatial location processes mainly. 2) Cue-evoked P2 and N2 components were related to the size of attentive region. 3) The processes of spatial location information were earlier than attentive scale information, which supported the theory that spatial selection is a prerequisite for correct processes of visual object information.