[Show abstract][Hide abstract] ABSTRACT: How attentional modulation on brain activities determines behavioral performance has been one of the most important issues in cognitive neuroscience. This issue has been addressed by comparing the temporal relationship between attentional modulations on neural activities and behavior. Our previous study measured the time course of attention with amplitude and phase coherence of steady-state visual evoked potential (SSVEP) and found that the modulation latency of phase coherence rather than that of amplitude was consistent with the latency of behavioral performance. In this study, as a complementary report, we compared the time course of visual attention shift measured by event-related potentials (ERPs) with that by target detection task. We developed a novel technique to compare ERPs with behavioral results and analyzed the EEG data in our previous study. Two sets of flickering stimulus at different frequencies were presented in the left and right visual hemifields, and a target or distracter pattern was presented randomly at various moments after an attention-cue presentation. The observers were asked to detect targets on the attended stimulus after the cue. We found that two ERP components, P300 and N2pc, were elicited by the target presented at the attended location. Time-course analyses revealed that attentional modulation of the P300 and N2pc amplitudes increased gradually until reaching a maximum and lasted at least 1.5 s after the cue onset, which is similar to the temporal dynamics of behavioral performance. However, attentional modulation of these ERP components started later than that of behavioral performance. Rather, the time course of attentional modulation of behavioral performance was more closely associated with that of the concurrently recorded SSVEPs analyzed. These results suggest that neural activities reflected not by either the P300 or N2pc, but by the SSVEPs, are the source of attentional modulation of behavioral performance.
PLoS ONE 01/2013; 8(8):e70922. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Endogenous attention modulates the amplitude and phase coherence of steady-state visual-evoked potentials (SSVEPs). In efforts to decipher the neural mechanisms of attentional modulation, we compared the time course of attentional modulation of SSVEP amplitude (thought to reflect the magnitude of neural population activity) and phase coherence (thought to reflect neural response synchronization). We presented two stimuli flickering at different frequencies in the left and right visual hemifields and asked observers to shift their attention to either stimulus. Our results demonstrated that attention increased SSVEP phase coherence earlier than it increased SSVEP amplitude, with a positive correlation between the attentional modulations of SSVEP phase coherence and amplitude. Furthermore, the behavioral dynamics of attention shifts were more closely associated with changes in phase coherence than with changes in amplitude. These results are consistent with the possibility that attention increases neural response synchronization, which in turn leads to increased neural population activity.
Journal of Cognitive Neuroscience 02/2012; 24(8):1779-93. · 4.49 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background / 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.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.
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.
Vision Sciences Society 11th Annual Meeting 2011; 06/2011