## 3 Results
### Induced Cortical Activity Changes in Source Space Topography to Selective Attention  
Examining the ERPs acquired at the sensor space was the initial step in determining the EEG data's quality. The induced cortical activity from the EEG data was able to be assessed due to the clear auditory components (like N1) discovered from the front-central channels.  
\(T\)-tests were taken between \"Up\" and \"Down\" in the spectrogram domain for week 1 and week 4, and of \"Up\"--\"Down\" in the spectrogram between week 4 and week 1 to analyze the difference of auditory modulation for both the Experimental Group and the Placebo Group. The cluster-based permutation tests were performed in the spectrogram which included the difference of attentional modulation between week 4 and week 1. Significantly different clusters were obtained within alpha and beta wave ranges (8-13 Hz and 24-29 Hz, respectively), in the Experimental Group, displayed as solid-line boxes in Figure 2A. These significant differences were not observed in the Placebo Group, so in order to indicate the regions of interest, the clusters from the Experimental Group were displayed as dotted line boxes in Figure 3A. As the clusters showed, attentional modulation was significantly improved only in the Experimental Group which received neurofeedback in every trial. When examining the alpha and beta waves in the preparatory timeline (from \(-\)1 to 0 s), each cluster appeared in the alpha and beta frequency ranges. The sensor space topographies and the source space topographies for both groups were averaged in the time-frequency range of the clusters from the Experimental Group, shown in Figure 2B,C and Figure 3B,C. The sensor space topographies of the beta oscillation within the cluster show a significantly stronger power on the parietal region of both hemispheres in week 4 of the Experimental Group. The source space topographies of the beta wave range indicate more power on MTG, STS, and IFG of both hemispheres in week 4 of the Experimental Group, illustrated in Figure 2B. The beta oscillations expand their role to anticipate selective attention on the given auditory cues during preparatory time periods in week 4 of the Experimental Group. Between week 1 and week 4 of the Placebo Group, there was no significant difference in the sensor space and source space topographies of the beta wave range during the preparatory time periods.  
Figure 2: Spectrograms and topographies of induced activities in the Experimental Group. (**A**) The t-score spectrograms of auditory modulation between “Up” and “Down” in week 1, week 4 and the t-score spectrogram of “Up” vs. “Down” between week 4 and week 1 are obtained during the neurofeedback training from the Experimental Group. The solid-line boxes indicate significantly different clusters within the alpha and beta wave ranges (8–13 Hz and 24–29 Hz, respectively), obtained by the cluster-based permutation tests from the Experimental Group [38]. (**B**) The topographies of the beta wave cluster are obtained in the preparatory time range before target speech onset (from \(-\)0.50 to \(-\)0.45 s) at the sensor space and source space. (**C**) The topographies of the alpha wave cluster are obtained in the preparatory time range before target speech onset (from \(-\)0.48 to \(-\)0.43 s) at the sensor space and source space.  
The sensor space topographies of the alpha wave range from the time periods of the cluster show a significantly strong power on the right parietal region in week 4 of the Experimental Group. The source space topographies of the alpha wave range show more power on IPS of the right hemisphere in week 4 of the Experimental Group in Figure 2C. The alpha oscillations increase to inhibit the left auditory stimuli during preparatory time periods in week 4 of the Experimental Group. During the preparatory time periods, there was no significant difference in the sensor space and source space topographies of the alpha wave range between week 1 and week 4 of the Placebo Group.