  With the increasing prevalence of 3D videos, investigating the differences of
viewing experiences between 2D and 3D videos has become an important issue. In
this study, we explored the cognitive load induced by 2D and 3D video stimuli
under various cognitive tasks utilizing electroencephalogram (EEG) data. We
also introduced the Cognitive Load Index (CLI), a metric which combines
{\theta} and {\alpha} oscillations to evaluate the cognitive differences. Four
video stimuli, each associated with typical cognitive tasks were adopted in our
experiments. Subjects were exposed to both 2D and 3D video stimuli, and the
corresponding EEG data were recorded. Then, we analyzed the power within the
0.5-45 Hz frequency of EEG data, and CLI was utilized to evaluate the brain
activity of different subjects. According to our experiments and analysis,
videos that involve simple observational tasks (P <0.05) consistently induced a
higher cognitive load in subjects when they were viewing 3D videos. However,
for videos that involve calculation tasks (P >0.05), the differences in
cognitive load induced by 2D and 3D video were not obvious. Thus, we concluded
that 3D videos could generally induce a higher cognitive load, but the extent
of the differences also depended on the contents of the video stimuli and the
viewing purpose.
