by James A Davidson comparing the work of the director with the Russian author.
 
"The most exemplary of Hitchcock's games is "find the director," in which the audience looks for Hitchcock's customary unbilled cameo appearances...Perhaps the most self-reflexive and playful of Hitchcock's cameo appearances occurs in Strangers on a Train (1951), a film in which game playing assumes a particularly high degree of importance...I find this a particularly Nabokovian moment in Hitchcock's films; I don't mean to suggest that Nabokov directly influenced this particular scene, just that this particular cameo functions visually as the type of pun or involuted joke that Nabokov often utilized in his writing. 
... Hitchcock also used the cameo as a foreshadowing device; in the opening of North by Northwest (1959) the doors of a bus shut in the director's face and this anticipates the crop dusting scene later in the film when Cary Grant has a bus door shut in his face. ...Nabokov too made what we might call cameo appearances in his novels, although the use of the first person narrative somewhat complicates what are and aren't "cameos" in his case. At the end of Bend Sinister (1947), the first book Nabokov wrote in America, the writer clearly makes a cameo. The bulk of the novel is written in third person, but at the story's conclusion Krug, the protagonist, is shot and the narrative is magically transformed into the first person as we find Nabokov, the writer, finishing his manuscript and getting up to look out his window. At this point he notes "I knew that the immortality I had conferred upon the poor fellow (Krug) was a slippery sophism, a play upon words." (Excerpt from Bend Sinister, page 216: "He saw the Toad crouching at the foot of the wall, shaking, dissolving, speeding up his shrill incantations, protecting his dimming face with his transparent arm, and Krug ran towards him, and just a fraction of an instant before another and better bullet hit him, he shouted again: You, you— and the wall vanished, like a rapidly withdrawn slide, and I stretched myself and got up from among the chaos of written and rewritten pages, to investigate the sudden twang that something had made in striking the wire netting of my window." Another cameo occurs at the end of Pnin (1957) when Nabokov roars into the narrative in his car as the professor hired to replace Pnin. Arguments could also be made that the forward to Lolita (1955, U.S. 1958) authored by John Ray, Jr., Ph.D. functions as a form of cameo appearance, but Nabokov's authorial voice is so strong through both this novel and Pale Fire that there is hardly any necessity for a cameo appearance as such in these two works.