Lev Vladimirovich Kuleshov (1899–1970) was a Soviet filmmaker and film theorist who taught at and helped establish the world's first film school, the Moscow Film School. For Kuleshov, the essence of the cinema was editing, the juxtaposition of one shot with another. To illustrate this principle, he created what has come to be known as the Kuleshov Experiment. In this now-famous editing exercise, shots of an actor were intercut with various meaningful images in order to show how editing changes viewers' interpretations of images.
In addition to his theoretical work, Kuleshov was an active director of feature-length films until 1943. Since 1943 Kuleshov was serving as the academic rector of Gerasimov Institute of Cinematography. Kuleshov edited together a short film in which a shot of the expressionless face of Tsarist matinee idol Ivan Mosjoukine was alternated with various other shots (a plate of soup, a girl in a coffin, a woman on a divan). The film was shown to an audience who believed that the expression on Mosjoukine's face was different each time he appeared, depending on whether he was "looking at" the plate of soup, the girl in the coffin, or the woman on the divan, showing an expression of hunger, grief or desire, respectively. Actually the footage of Mosjoukine was the same shot repeated over and over again. Vsevolod Pudovkin (who later claimed to have been the co-creator of the experiment) described in 1929 how the audience "raved about the acting... the heavy pensiveness of his mood over the forgotten soup, were touched and moved by the deep sorrow with which he looked on the dead child, and noted the lust with which he observed the woman. But we knew that in all three cases the face was exactly the same. Kuleshov used the experiment to indicate the usefulness and effectiveness of film editing. The implication is that viewers brought their own emotional reactions to this sequence of images, and then moreover attributed those reactions to the actor, investing his impassive face with their own feelings. Kuleshov believed this, along with montage, had to be the basis of cinema as an independent art form. The effect has also been studied by psychologists, and is well-known among modern filmmakers. Alfred Hitchcock refers to the effect in his conversations with François Truffaut, using actor James Stewart as the example.
Hitchcock, in the famous "Definition of Happiness" interview, also explains in detail many types of editing. The final form, which he calls "pure editing", is explained visually using the Kuleshov effect. In the first version of the example, Hitchcock is squinting, and the audience sees footage of a woman with a baby. The screen then returns to Hitchcock's face, now smiling. In effect, he is a kind old man. In the second example, the woman and baby are replaced with a woman in a bikini, to which Hitchcock exclaims, "Now look, he has become the dirty old man." Kuleshov demonstrated the necessity of considering montage as the basic tool of cinema art. In Kuleshov's view, the cinema consists of fragments and the assembly of those fragments, the assembly of elements which in reality are distinct. It is therefore not the content of the images in a film which is important, but their combination. The raw materials of such an art work need not be original, but are pre-fabricated elements which can be disassembled and re-assembled by the artist into new juxtapositions.
I found this effect repeated and developed further in ‘Forest Gump’.