Music provides a very powerful retrieval cue. Music is more than just an additional piece of information, it is an integrated cue that provides information about the nature of the text. The music defines the length of lines, chunks words and phrases, identifies the number of syllables, sets the pattern of stressed and unstressed syllables within the text. Thus, the music acts as a frame within which the text is tightly fit. That frame can connect words at encoding, limit retrieval search, as well as constrain guessing or recreation at retrieval.
Lisa Stewart on 27 Sep 10includes a section about song lyrics and a good introduction to the cognitive aspects of memory Excerpt: "The experimental data corroborate our intuition that the memory representation for lyrics seems to be tied into the memory representation for melody (Serafine, Crowder, and Repp 1984). Further evidence of this comes from a case report of a musician who suffered a stroke caused by blockage of the right cerebral artery. After the stroke, he was able to recognize songs played on the piano if they were associated with words (even though the words weren't being presented to him), but he was unable to recognize songs that were purely instrumentals (Steinke, Cuddy, and Jacobson 1995)."