In its concentration of interest upon the protagonists, Macbeth can be seen as Shakespeare's experiment in unity of focus, whose chief appeal arises from the struggles of the central characters with each other and with the infernal powers that inspire or govern them. Over the centuries, the vision of directors like Welles, Nunn and Polanski, as well as the eloquent talents of actors like Garrick, Siddons, Olivier and McKellen have contributed to the central debate of the play: Who or what is culpable? Bernice W. Kliman, in her analysis of Macbeth in performance, examines major productions of the play on both stage and screen, thereby inviting the reader to contemplate directors' and actors' choices for what is arguably Shakespeare's most compelling play.