A revelatory moment in Miriam Bäckström’s impressive retrospective “The Opposite of Me Is I” was her documentary-style video Rebecka, 2004, in which she shifts between interrogating and directing the actress Rebecka Hemse. Hemse is an accomplished performer with a beguiling range of subtle expressions; in this case, they are charged with enigmatic allure by the ambiguity of her character. But when is this actress not performing? Is she ever being herself? “If I consider fiction to be more authentic,” she wonders, “why leave it at all?” Moments later, Bäckström asks pointedly, “When are you most