In their 1934 short film Oliver the Eighth, Hollywood comics Stan Laurel and Oliver Hardy spend a night in a spooky old house as guests of a sinister woman and her mad butler.

Just when the knife-wielding femme fatale is about to make Olly her eighth murder victim, he awakes to find himself being shaved by Stan in a barber's shop. It has all been a dream.

This corny plot device had 'em rolling in the aisles in the movies' age of innocence and also crops up in more serious films like Fritz Lang's The Woman in the Window (1944). Today it seems somewhat quaint.

Dreams and film have a long and complex history and dreams have played a part in countless movies since the very earliest days of cinema in the 1890s.

Many memorable films like The Wizard of Oz (1939) are basically glorified dream sequences while others like Alfred Hitchcock's Vertigo (1958) employ short, but highly effective dream scenes that are central to an understanding of the story.

The American director Orson Welles described film as a 'ribbon of dreams.'

He wrote: 'The camera is much more than a recording apparatus. It is a medium via which messages reach us from another world that is not ours and that brings us to the heart of a great secret. Here magic begins.'

Indeed a film can voyage freely across both space and time - like a dream. In a very real sense, all film is dream.

The British director John Boorman says he tries to reach the audience's 'dream world' and the 'twilight of their thoughts' where 'real communication' takes place.

This concept is based on the belief that the dreams people have at night have deep and mysterious significance.

Boorman says black and white connects audiences to dreams and the unconscious more than colour. He shot The General (1998) in b&w though commercial pressures stopped him doing the same with most of his other films.

The psychoanalyst Sigmund Freud (1856-1939) said that dreams are a 'royal road' to an understanding of the part of the human mind that remains unconscious. The unconscious, he believed, was like an iceberg with by far the greater part remaining hidden from view.

The first major film about psychoanalysis was Alfred Hitchcock's Spellbound (1945) in which the symbolism of an amnesiac's dream provides clues to a murder mystery.

Freud's ideas and especially dream images also influenced the Surrealist movement that began in Europe in the 1920s. One of the first Surrealist films was Un Chien Andalou (1928), in which the director Luis Buñuel worked with the artist Salvador Dalí.

Not all cinematic dreams are mind-blowingly profound, of course. The 17-minute dream sequence/ballet in An American in Paris (1951) is fun and light-hearted.

The sequences involving dreams in Ingmar Bergman's Wild Strawberries (1957) are, however, much darker and packed with terrifying meaning.

The dream sequence in Boorman's Point Blank (1967) is, perhaps, the entire film while Buñuel's The Discreet Charm of the Bourgeoisie (1972) makes use of dreams within a dream within a dream.

Meanwhile, Ribbon of Dreams (2002) directed by Philip W Chung looked at dreams in the sense of people's hopes and aspirations for the future. This charming short film celebrated the contribution Asian Americans made to Hollywood movies over the years.

Mark Long, London, 2004