# Closed-Loop Cognitive-Driven Gain Control of Competing Sounds Using Auditory Attention Decoding
## 2 Methods
### Correlation Coefficient Generation
This practicing phase could simply be an extended version of the closedloop phase with many sessions where the participants can gather enough experience to fully master (i.e. find an intelligent way to control) the cognitive-driven gain controller system. Although the application of the proposed cognitive-driven gain controller system was limited to acoustic scenarios with two competing speakers, it was shown in Reference [10] that open-loop AAD is feasible for an acoustic scenario with four competing speakers when using perfectly separated clean speech signals for decoding. In addition, the evaluation of the proposed system was limited to acoustic scenarios with non-moving speakers and with speakers located on opposite sides of the listener, whereas in real-world conditions speakers may move and may be located on the same side of the listener. Therefore, it would certainly be interesting as future work to investigate the performance of (an extension of) the proposed cognitive-driven speech enhancement system for more realistic acoustic scenarios. The application of the proposed cognitive-driven gain controller system is obviously not limited to hearing devices. The system could also be used, e.g., for virtual reality (VR) that simulates a remote environment, e.g., for entertainment, training and medicine. It could be used to adapt the simulated world based on the auditory attention of the VR user. ## 5 Conclusions

In this paper, we proposed a closed-loop gain system which cognitively steers an adaptive gain controller based on real-time AAD for a scenario with two competing speakers. The real-time AAD infers the probabilistic attention measures of the attended and the unattended speaker from EEG recordings of the listener and the speech signals of both speakers. Based on these probabilistic attention measures, the adaptive gain controller amplifies the identified attended speaker and attenuates the identified unattended speaker. The loop of cognitive-driven gain control is then closed by presenting the amplified attended speaker and the attenuated unattended speaker via loudspeakers. The experimental results demonstrate the feasibility of the proposed closed-loop cognitive-driven gain controller system (both using AAD algorithms based on GLM and SSM), enabling the listener to interact with the system in real-time. Although there is a significant delay to detect attention switches, which causes the attended speaker to be wrongly attenuated and the unattended speaker to be wrongly amplified for some time, the proposed closed-loop system is able to improve the SIR between the attended and the unattended speaker. Moreover, the subjective evaluation results show that the proposed closed-loop cognitive-driven system demands a similar perceived level of cognitive effort to follow the attended speaker, to ignore the unattended speaker, and to switch attention between both speakers compared to open-loop AAD. With this work, an attempt was made to bring closed-loop cognitive-driven speech enhancement closer to real-world applications. Conceptualization, A.A. and E.F.; Data curation, A.A.; Formal analysis, A.A.; Funding acquisition, E.F., M.S. and H.P. ; Investigation, A.A., E.F., M.S. and H.P. ; Methodology, A.A., E.F. and M.S. ; Project administration, H.P. ; Software, A.A.; Supervision, A.A., E.F., M.S. and H.P. ; Validation, A.A.; Visualization, A.A.; Writing--original draft, A.A.; Writing--review & editing, A.A. and S.D. All authors have read and agreed to the published version of the manuscript. This work was supported by WS Audiology and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy--EXC 2177/1-Project ID 390895286. The study was carried out in accordance with the Declaration of Helsinki. Not applicable. **Acknowledgments:** The authors would like to thank [PERSON] and [PERSON] for their fruitful discussions concerning AAD and [PERSON] and [PERSON] for their assistance in EEG data collection. ## Conflicts of Interest

The authors declare no conflict of interest.