*3.4.1 Performance metrics*

24 out of 28 articles use quantitative measurement to test the learning outcomes, whereas four use qualitative metrics to report the participants' performance (see Appendix 2). One article has not tested their result [50]. One study [54] only presents a description indicating that a user who was not an expected volunteer could control the mental task easily in a short duration. We will not consider these two articles in metrics recommendations. Therefore, the following paragraph will indicate the commonly used performance metrics in the qualitative and quantitative groups.

Appendix 2 lists several performance metrics used for learning outcomes measurement (see Appendix 2). Twenty-four articles used quantitative metrics for MI-BCI gaming mode measurement. The two most frequently used metric is accuracy (16/24) and performance score, or game score/rate (5/24). In four articles using qualitative evaluation, the commonly used metric is the game experience questionnaire (GEQ ) (2/4). In the discussion part, we will present a detailed introduction and analysis.

## *3.4.2 Training issue*

The existing issues identified in the experiment are reported from the first designed MI-BCI game till now (see Appendix 2). We found six main issues: ① environmental background and distraction (3/28), ② trial length relevant fatigue (4/28), ③ *Improving the Brain-Computer Interface Learning Process with Gamification in Motor Imagery:… DOI: http://dx.doi.org/10.5772/intechopen.105715*


**Table 8.**

*Summarization of training issue and its considerations.*

performance variation (4/28), ④ increasing false positive rate (2/28), ⑤ performance decrease (2/28), ⑥ toughness to complete game (2/28). **Table 8** below shows the summarization of each issue with its consideration. We gave a detailed explanation in the discussion part.
