Stefan has volunteered to participate in an experiment studying vision in which he will wear a pair of glasses that invert his vision. because of after about a week, he is able to perform his usual activities, like riding a bike or reading a book.

   Perceptual adaptation

Explanation:  Since Stefan was involved in an experiment concerning the study of vision and the wearing of glasses that invert his vision, it took some time to perform a perceptual adaptation. Perceptual adaptation is, in fact, the means by which the brain perceives differences, most often as in this case in the field of vision, which Stefan witnessed.

there are no options provided but you can choose among the following gender-neutral pronouns: zir, hir, eir, vis, tem, eir.

in the normal course of maintaining a pronoun-antecedent agreement, we could have used the words his or her but since we are also required to use gender-neutral language, we need to replace it with its equivalent gender-neutral pronoun.