Sounding Out The City

A personal stereo is control.  In all situations that were described people used it to alter their environment.  Whether to block out unwanted stimuli or to make a situation more "in tune" to their mood users attempt to hold some kind of control. Control is a basic need in a persons life. By controlling stimuli you can control your environment. This control leads to a fantasy world.
The ability to escape into this world is universally understood. So when someone is in their own world it pushes other people away. Not because other people are offended but because it is seen as rude to break someone out of their world for no reason.  This reinforces the idea that one is in their own world.
Without the imagined potential for human interaction the brain is able to process other things.  If the person focuses on their music they can pass time faster than usual because they will not focus on other things making time harder to judge.  When one is on public transportation most of the time they are trying to avoid interpersonal contact so the desire to focus on one's dream world becomes greater thereby also increasing the rate at which time is dilated.
The more a person uses a personal stereo the more addicted they become to the control. This is evident in the interviews about how people feel when they do not use it.  They feel bored or have an "empty feeling."  The empty space is not just about having some music fill the void, it is about having an interaction on your own terms.
Today the ability to control interactions through intermediation has become widespread. Text messages have replaced phone calls because a phone call has become too much of an interjection in someone else's life.  This stems from the same need for control exhibited by the widespread use of personal stereos.  With control over stimuli achieved people feel more at home wherever they are.  After all a home is only a way to control environmental stimuli, i.e. temperature, wind, rain.