Visual Cortex
Like the name states, the visual cortex is involved with the processing and interpreting of visual images. The information that is seen by the eyes are transmitted to the visual cortex where it can be interpreted. The image is also upside down before it reaches the visual cortex, so one of the functions of the visual cortex is to flip the image right-side up.
How does this relate to music?
The visual cortex is stimulated by listening to music and can provoke the listener to picture images which match the music. As we listen to music we conjure up colors in our minds. Research has shown that no matter which culture you come from you will associate the same music with the same colors. Dull, dark colors are associated with sad music and light and bright colors are associated with happy music. The brain associates the emotional content of the music with the colors we associate with the same emotions.
Music also manipulates the way we see the world. It changes and affects our mood, which affects how we see the world.