Fig 1.
A schematic diagram of the counting and meaning task.
During the pre-imitation phase (left), participants were requested to count number of hand movements the actor made in the counting task. In the meaning task, in contrast, they were instructed to guess what the sign speech meant. In the imitation phase (middle), the participants were required to imitate a sign speech, following the actor in both tasks. The post-imitation phase (right) was identical to the pre-imitation phase except that the participants needed to select one of three options for the answer in the meaning task.
Fig 2.
Spatial layout of the EEG sensors.
Labels with an alphabet followed by a digit indicate the sensors matching the international 10-20 system. Labels with a number without alphabets indicate the sensor positions designated by the EGI Netstation registration system. The present study focused on EEG signals from the central channels (C3, Cz, and C4) and occipital ones (O1, Oz, and O2).
Fig 3.
Scatter plots of the contribution rate for the first and second components obtained from the independent component analysis performed on time-series data of mu- and alpha-oscillation.
Each blue dot corresponds with the contribution rates belonging to the central regions, while orange corresponds with the rates to the occipital regions.
Fig 4.
Time-series mu- and alpha-power in three trial phases (pre-imitation, imitation, and post-imitation) of the counting and meaning task.
In the counting task, distinctive mu-suppressions were found in the pre- and post-imitation phases, while the suppression was moderate in the imitation phase (1st row). Similar mu-power transition was seen in the meaning task (3rd row). Alpha-suppressions were found in the pre- and post-imitation phases while such suppression was not observed when imitating body movements in the counting (2nd row) and meaning task (4th row). The horizontal axes represent time (-2s to 4s) and the vertical ones represent power of the mu/alpha frequency. The dashed vertical lines indicate onsets of movies. The shaded area shows standard errors of the mean.
Fig 5.
Mean mu- and alpha-suppression in three trial phases of the counting (blue boxplots) and meaning task (orange box plots).
Mu-suppressions were found in the pre- and post-imitation phases in both tasks (left panel). Similarly, alpha-suppressions were observed in the pre- and post- imitation phases in both tasks (right panel). It was also found that power of mu was significantly smaller than that of alpha during the imitation phase of the meaning task. There was a trend toward a significant difference between power of mu and that of alpha during the imitation phase of the counting task. The middle lines indicate the mean values of power ratio relative to the baseline, while the notch indicates the median. The whiskers extend 1.5 times the interquartile range from the top and bottom of the box.
Fig 6.
Time-series beta-power in three trial phases of the counting and meaning task.
Beta-suppression in the central regions was evident in the pre- and post-imitation phases of the counting (1st row) and meaning task (3rd row), while it was moderate in the imitation phases. Beta-suppression in the occipital regions was also evident in the pre- and post-imitation phases of the counting (2nd row) and meaning task (4th row), but not observable in the imitation phases.
Fig 7.
Beta-suppression in three trial phases of the counting (blue boxplots) and meaning task (orange box plots).
Beta-suppression was observed in three phases in the central regions in both tasks (left panel). By contrast, the suppression was observed in the pre- and post-imitation phases but not during imitation in the occipital regions (right panel). It was also found that beta-suppression during the imitation phase of the meaning task was significantly greater in the central region than in the occipital region. The middle lines indicate the mean values of power ratio relative to the baseline, while the notch indicates the median. The whiskers extend 1.5 times the interquartile range from the top and bottom of the box.