  Visual imagery is an intuitive brain-computer interface paradigm, referring
to the emergence of the visual scene. Despite its convenience, analysis of its
intrinsic characteristics is limited. In this study, we demonstrate the effect
of time interval and channel selection that affects the decoding performance of
the multi-class visual imagery. We divided the epoch into time intervals of 0-1
s and 1-2 s and performed six-class classification in three different brain
regions: whole brain, visual cortex, and prefrontal cortex. In the time
interval, 0-1 s group showed 24.2 % of average classification accuracy, which
was significantly higher than the 1-2 s group in the prefrontal cortex. In the
three different regions, the classification accuracy of the prefrontal cortex
showed significantly higher performance than the visual cortex in 0-1 s
interval group, implying the cognitive arousal during the visual imagery. This
finding would provide crucial information in improving the decoding
performance.
