Recently, having watched a restored version of Fred Zinnemann's The Wave (1935), shot on location in Mexico with non-professional actors recruited among the local fishermen - a film that anticipates Italian neo-realism - my belief that professional film acting is vastly overrated was reanimated. Film acting is the least skilled of all the performing arts and the one that needs least training. As has been proved time and again, anyone can be picked off the streets and be made to give a great performance on screen. Can one imagine doing the same with a ballet dancer, opera singer or classical pianist? As Spencer Tracy once remarked, "All you need to do is know your lines and don't bump into the furniture."

This was has been apparent ever since Lev Kuleshov's experiment with montage in the early 1920s. Kuleshov edited a short film in which shots of the face of the celebrated actor Ivan Mosjoukine were alternated with various other shots (a plate of soup, a pretty girl, an old woman in a coffin). When the film was shown to an audience, they praised Mosjoukine's acting as he showed expressions of hunger, desire and sorrow as he "looked at" the three different things, believing the expression on his face was different each time. Actually, the footage of Mosjoukin's rather expressionless face was identical.

It is a fact that almost anyone can be a good film actor - old, young, infirm, intellectual, stupid, good-looking or ugly. Even animals can give wonderful performances: witness Robert Bresson's Balthazar. Among Bresson's other non-professional "actors" were the unforgettable Nadine Nortier in Mouchette, Claude Laydu in Diary of a Country Priest, and Martin La Salle in Pickpocket.

For Bresson, "the less the actors know about the film, the more I like it. I only ask them, 'You are sitting here - look at that door.' Then we rehearse that 10 times. Then I say, 'When we are there, you say this sentence. Say it as calmly as possible, as mechanically as possible.' In the action, you see, what this girl or this boy has got inside takes place without their knowing it." Some of the greatest performances in cinema have been by those who had never acted before or since: Falconetti in Carl Dreyer's The Passion of Joan of Arc; Lamberto Maggiorani and Enzo Staiola in Vittorio De Sica's Bicycle Thieves, and Carlo Battisti in De Sica's Umberto D; and 13-year-old Edmund Meschke in Roberto Rossellini's Germany Year Zero. Children, in general, come across as brilliant actors on screen, as can be seen in several Iranian films over the last few years. But, whether children, adults or animals, actors are only as good as their directors. Actors are to the film director as clay is to the sculptor. Think of actors that are associated with one director and are never as good without them: for example Kinuyo Tanaka and Kenji Mizoguchi, Chishu Ryu and Yasujiro Ozu, Anna Karina and Jean-Luc Godard, Toshiro Mifune and Akira Kurosawa, Jean-Pierre Leaud with both Jean-Luc Godard and Francois Truffaut, Edith Scob and Georges Franju, Monica Vitti and Michelangelo Antonioni.

However, I exempt film stars from this discussion because they impart complex images containing multiple meanings, relating to their perceived off-screen as much as to their onscreen personae. They are iconic presences rather than performers, who rely on their looks and manufactured personalities. Audiences, from the very beginning of the star system, which still exists, have not paid to see them act, but to watch them behave as they are expected to behave.

Ronald Bergan