I noticed something interesting: in Google Scholar, when you punch in Young as author and the reasonable search terms 'rat' 'maze' 'sand' restricted to before Feynman's lecture, only 3 items pop up.

I don't have access to the 3, so I've requested them: http://lesswrong.com/lw/ji3/lesswrong_help_desk_free_paper_downloads_and_more/auye

(Frustratingly, Young wrote a whole textbook on rats/mice available on the Internet Archive - the year before Feynman says he did the experiment! Another textbook, Emotion in man and animal: its nature and dynamic basis, isn't on IA but is in Google Books; checking it with a few keywords like 'sand' and 'smell' and 'third', doesn't seem to throw up any particularly good hits.)