I wouldn't be so sure about "purposefully": they are reading the same book (http://languagelog.ldc.upenn.edu/nll/?p=478 http://languagelog.ldc.upenn.edu/nll/?p=

I wouldn't be so sure about "purposefully": they are reading the same book (http://languagelog.ldc.upenn.edu/nll/?p=478 http://languagelog.ldc.upenn.edu/nll/?p=478, the book is https://books.google.ca/books?id=525HX623L_cC https://books.google.ca/books?id=525HX623L_cC), but it seems on page 90 instead of 116. Brooks doesn't link to the study itself, not mentioning authors' names, so I think they made a guess about which study he meant.