when confronted with a situation falling within their specialized field, experts can process information in large chunks. Whereas laymen and novices tend to process things one small piece at a time; and on top of that, they flail around a lot.
Actually, that's a load of nonsense:
1) With programs that are *actually* large, you won't find "experts" that consume them in "large" chunks, unless they use very small fonts.
2) With programs that are new to the readers, you might have to read in toto them anyway. There's no guarantee that the *actual* dependencies in the code will allow you to read it in a limited or strictly hierarchical fashion. You gotta read what you gotta read. It's not like people will only shove neat and pleasurable code on you in real life. If the code is messy, your reading of it will most likely be messy, too. Especially if you hit duplications and have "wait a minute, didn't I see this somewhere else? Lemme check" moments.