“Could acceptability and usability of BCI user training procedures be (the) key to out of the lab BCI use?"

EEG-based Mental-Task BCIs (MT-BCIs) are promising technologies to favour restoration or improvement of motor and cognitive performances, notably, in stroke patients and athletes. Nonetheless, several scientific challenges still have to be taken up before these technologies are usable and actually used outside laboratories. Most of the research in the field focuses on improving MT-BCI efficiency in terms of classification accuracy or information transfer rate for instance. Yet, despite intensive efforts, it is estimated that 10 to 30% of users are still unable to control an MT-BCI while average control performances remain low. Our hypothesis is that improving MT-BCI efficiency per se is not sufficient to democratise their usage. We introduce two complementary dimensions, namely MT-BCI acceptability and usable. We will define them and demonstrate that, while they are still mostly neglected, considering them when designing MT-BCI systems might be key, if not the key, to make MT-BCIs actually used outside laboratories.