We have put here a few pointers to papers and tutorials that provide some technical background to PeARS.
A short system description was published at WWW2016 and is available here. We have done a first evaluation of the accuracy of the system, which was published at the *SEM conference and is downloadable here.
PeARS is powered by a technique called distributional semantics. A very simple introduction to distributional semantics is available here. If you are interested in a more technical and comprehensive introduction, check out the papers by Turney and Pantel (2010) or Clark (2012). If you are hooked... have a look at this rather long bibliography, with many papers covering topics from formal meaning representations to multimodal semantics.
After all this reading, if you want to get your hands dirty with distributional semantics, you can try out the tutorials (complete with code to play with) in this GitHub repo.