The audio-visual relations in Hitchock's Psycho are very complex and telling throughout his film. For the first 40 minutes, the film is used to slowly bring the audience into the world of their soon to be protagonist, Marion. This is achieved mostly through POV shots along with internal and external-diegetic sound, and non-diegetic sound. To further discuss this concept, the famous shower scene will be broken down to illustrate how Hitchock brilliantly uses this method of storytelling through audio and visual techniques. .
At this point of the story the audience have become the eyes and ears of Marion and have learned that she is going to return the money the next day. She flushes a paper containing her estimation of money owed down the toilet, symbolically "flushing" her sins away. All the audience can hear are the sounds of the flushing toilet, and nothing else. She then decides to take a shower , cleverly representing the cleansing of her sin as well. The audience continues to follow her motions: her turning the knobs of the shower, followed by the sound of the water coming out of the shower. This scene is also perfectly shot with the subjective view of the shower head pouring its water onto her. The audience truly feels these acts of cleansing, for throughout this whole scene all the audience hears are the diegetic sounds of what Marion would actually be hearing.
Then, from all of Marion's POV shots and internal dialogue that runs through the whole film, there is a change. The audience is given the opportunity to see something their protagonist does not see. Marion is in the foreground camera right, while in the background camera left there is a shadowy figure closing in on Marion without a sound. The figure rips open the shower curtain, breaking the "silence" of her cleansing. At this point, Hitchock minimalizes the diegetic sound of the curtain, opting instead to throw in one of best uses of non-diegetic sounds of film history; the screeching violins.