The process of filmmaking is both an art and an industry. Films were originally recorded onto plastic film which was shown through a movie projector onto a large screen (in other words, an analog recording process). The adoption of CGI-based special effects led to the use of digital intermediates. Most contemporary films are now fully digital through the entire process of production, distribution, and exhibition from start to finish. Films recorded in analog form traditionally included an optical soundtrack, which is a graphic recording of the spoken words, music and other sounds that are to accompany the images. It runs along a portion of the film exclusively reserved for it and is not projected. Films are cultural artifacts created by specific cultures. They reflect those cultures, and, in turn, affect them. Film is considered to be an important art form, a source of popular entertainment, and a powerful medium for educating—or indoctrinating—citizens. The visual basis of film gives it a universal power of communication. Some films have become popular worldwide attractions by using dubbing or subtitles to translate the dialog into the language of the viewer. Some have criticized the film industry's glorification of violence and its sexist treatment of women. The individual images that make up a film are called frames. During projection of traditional films, a rotating shutter causes intervals of darkness as each frame in turn is moved into position to be projected, but the viewer does not notice the interruptions because of an effect known as persistence of vision, whereby the eye retains a visual image for a fraction of a second after the source has been removed. The perception of motion is due to a psychological effect called phi phenomenon. The name "film" originates from the fact that photographic film (also called film stock) has historically been the medium for recording and displaying motion pictures. Many other terms exist for an individual motion picture, including picture, picture show, moving picture, photoplay and flick. The most common term in the United States is movie, while in Europe film is preferred. Terms for the field in general include the big screen, the silver screen, the movies and cinema; the latter is commonly used in scholarly texts and critical essays, especially by European writers. In early years, the word sheet was sometimes used instead of screen.