61 Mortimer Jerome Adler and Charles Van Doren, How to Read a Book, Rev. and updated ed (New York: Simon and Schuster, 1972), 45.

I see some of the sense of this footnote, which helps to establish some ethos by calling to mind Adler/Van Doren's classic, but this particular page in their text is really about paying enough attention not to fall asleep and thus doesn't underline Scheper's point as well as references to other portions of their book about goals and active reading.