Being around people usually engages various parts of the brain that are involved in being aware of the local situation. Even if you're not interacting to someone, some amount of monitoring happens to maintain the brain's model of the local environment that we actually experience. This would include stuff like tracing the locations of people/stuff in the room, checks of stuff like body language or subtle social indicators, and probably a long list of other tiny checks that we never really notice consciously.
The problem is that some of the areas of the brain that do that processing are also used when handling other complex tasks such as programming. This overloading of processing areas will vary from person to person, of course.
This problem is the main reason I could never work in an open office, and have serious productivity problems even ion an office shared with only one other person. It's not that they are interrupting constantly or otherwise distracting in the commonly-used sense. If there are people around, I have to be aware of them, which wastes mental CPU time and introduces cache-flushing context switches at annoying times.
The problem is that some of the areas of the brain that do that processing are also used when handling other complex tasks such as programming. This overloading of processing areas will vary from person to person, of course.
This problem is the main reason I could never work in an open office, and have serious productivity problems even ion an office shared with only one other person. It's not that they are interrupting constantly or otherwise distracting in the commonly-used sense. If there are people around, I have to be aware of them, which wastes mental CPU time and introduces cache-flushing context switches at annoying times.