Can anyone point to useful literature for non-experts about the history of the development of the various chants in the Divine Office? I'm puzzled by the question: Why are the Responds so simple in the little hours and Compline, and so (relatively) ornate at Matins? Yes, the question might be answered "It's Matins, so of course they're more ornate, Silly!", but just as the Introit verses developed differently from the Offertory verse (one used to include the entire psalm, if I recall correctly, but the other never did, for example, and one is psalm-toned while the fundamental characteristic of other is its ornate or decorative or Baroque quality.

Anyway, comments here are welcome, but so are relevant text recommendations.