“…The BCI performance may be enhanced in various ways by selecting the optimal pre-processing techniques [ 24 , 25 , 26 ], features [ 25 , 27 , 28 , 29 , 30 ], classifiers [ 29 , 31 ], or by focusing on user instructions and training [ 23 , 32 , 33 ]. By improving the BCI performance, the patients’ perceived control and frustration improve as well [ 34 , 35 , 36 , 37 , 38 , 39 , 40 ], which may help them maintain interest in the training. Moreover, frustration has a detrimental effect on BCI performance with increasing frustration leading to worse BCI performance [ 39 ].…”