Before revision:  (i) Most domain adaptation  methods are designed for labeled source and unlabeled target domain whereas BCI tasks generally have multiple annotated domains.
After revision:  (i) Most domain adaptation techniques. Among those, to our knowledge, an adversarial learning has shown its potential in BCIs. In the meantime, it is known that adversarial learning-based domain adaptation methods are designed for labeled source and unlabeled target domain whereas BCI tasks generally have multiple annotated domains.