Attention boosts neural population response via neural response synchronization

Abstract

[Purpose] Visual attention enhances neural responses to an attended stimulus by neural response gain control. It has been also pointed out that attentional enhancements of neural responses originate from neural response synchronization (e.g. Fries et al., 2001; Kim et al., 2007). In this study, we adopted a steady-state visual evoked potential (SSVEP) technique in an attempt to investigate the relationship between the neural response amplitude and the neural response synchronization. [Experiment] SSVEP is an oscillatory brain potential evoked by a continuously flickering visual stimulation and can be identified as EEG components corresponding to the flicker frequencies. It has been shown that the visual attention modulates the amplitude and phase of the SSVEP. We recorded SSVEPs for two stimuli flickered at different temporal frequencies which were presented on the left and right sides of the fixation. An arrow-shape cue was presented on the center of the display to control participants' state of attention. Participants were instructed to shift their attention to a flickering stimulus in the side pointed by the cue. We analyzed the amplitude (thought to reflect the magnitude of neural population response) and phase coherence (thought to reflect neural response synchronization) of SSVEP. [Results] Both the SSVEP amplitude and phase coherence were increased by visual attention and the correlation between the two measures was very high (r > 0.55). Time course analysis of the two SSVEP measures showed that attentional modulation for the phase coherence started earlier than that for the amplitude. These results indicate that visual attention boosts neural population response via neural response synchronization.