Ongoing Global Phase Pattern and Visual Signal Detection
When a stimulus is present on the threshold, it appears that we perceive it by chance. Previous electroencephalogram (EEG) studies have reported that the prestimulus phase and amplitude of alpha band activity at a single channel were correlated with visual perception. However, these factors cannot explain a major portion of fluctuations in perception. We hypothesized that another activity in the prestimulus period should predict the success/failure of perception. This would be phase coherence across cortical areas. We conducted a simple visual discrimination task in which subjects reported whether they had perceived a tiny flash of light by pressing one of two keys. We calculated inter-trial coherence (ITC) of the alpha band phase for the hit and miss trials, respectively. We found that the peak ITC times between hit and miss trials were 250–400 ms apart. These results imply that spontaneous formation of coherent alpha band activity and its timing are crucial in the processing of visual perception. These results suggest the importance of neural dynamics in the form of coherent alpha band activities in the frontal and occipital regions for the processing of visual perception.
KeywordsPhase Coherence Alpha Band Left Frontal Region Prestimulus Activity Alpha Band Activity
We thank H. Nakatani and J. Ito for helpful discussion. This study was partially funded by MEXT Grant-in-Aid for scientific research (No. 21120004: K Kaneko, No. 21120005: K Kitajo and YY), JST PRESTO program (K Kitajo) and by JSPS Fellows (DS).
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