Today in class we explored absolute and difference thresholds, particularly as they relate to "subliminal sensation." I usually have quite a few students interested in exploring these things on their own, so to that end here are the links to the musical backmasking site we looked at in class and another that examines "reverse speech" in recorded speech. As you probably can guess, based on the psychological research about subliminal messaging, I don't give a whole lot of weight to the claims made by some of the authors of these sites, but you should feel free to explore them on your own in light of the research we discussed in class.
And for fun...this video clip from the popular Monty Python series pokes fun at the inconvenience of working with people who have varying absolute thresholds for hearing. Thanks, Nathan S., for passing this on.