The best answer to that that I know of is by http://en.wikipedia.org/wiki/Adriaan_de_Groot: "De Groot found that much of what is important in choosing a move occurs during the first few seconds of exposure to a new position. Four stages in the task of choosing the next move were noted. The first stage was the 'orientation phase', in which the subject assessed the situation and determined a very general idea of what to do next. The second stage, the 'exploration phase' was manifested by looking at some branches of the game tree. The third stage, or 'investigation phase' resulted in the subject choosing a probable best move. Finally, in the fourth stage, the 'proof phase', saw the subject confirming with him/herself that the results of the investigation were valid."

IIRC, in phase one, experts see wo or three moves to look deeper into. Non-experts see many more.

I recommend reading "het denken van den schaker" if this interests you. It is very readable by laypersons (and a translation in English exists)