Attention seems to me, an important part, often overlooked. Attention deals both with input and processing. When you think about a problem, you are attending to it; -- just as you can attend to something which provides inputs from the external world. Both of your examples are externals, as they are the result of responding to a perceived difference or unexpected similarity (which is really just a type of difference -- as in a search) in the environment. People perceive distraction (as in your #2) as a reflex, not something that they willfully do. However, in a search, people may seem to willfully scan for something particular. -- On the other hand, the search may not be consciously directed. People have a limited input space. For example, you can only see so much of a scene with your eyes without moving your head, eyes, and/or body. So, to attend to something external is to effect a change in the parameters of your input space. For example, to feel the texture of a cloth, you must effect your hand, arm, and body -- in co-ordination with information from your eyes and body (inputs) -- to touch the cloth. Similarly, concepts also have limited spaces (7+/-2 chunks). So to attend to concepts is to change the chunks governing the thought process. Attending is the changing of parameters of input and concept space. The change happens on detection of difference or unexpected similarity within the current spaces. Once attention shifts, more detailed or more global differences/similarity can be detected. Now, if you stare at a scene for too long, you may become bored, because the scene becomes one thing -- without differences. And so, you will either zoom in or out (change input space parameters). -- Dimitry