In the sciences or social sciences, primary sources report the results of an experiment. These studies are also called "empirical studies".
Keep Salkind's advice in mind when you write your own literature review for your proposal:
" . . . your best bet is to include primary sources in your literature review, with some secondary sources to help make your case. Do not even think about including general sources information is secondhand, however, and you do not want to build an argument based on someone else's interpretation of an idea or concept" (Salkind, 2009, p. 49).
Source: Salkind, N.J. (2009) Exploring Research (7th ed.). Upper Saddle River, NJ: Pearson/ Prentice Hall Higher Education.
The most efficient way to identify primary research on your topic is to search a research database like PsycINFO or ERIC and then use the database limits to retrieve appropriate results. Though these two databases use different terms to retrieve primary research, the principle is very much the same. You can find primary research in other research databases, like Education Research Complete, but those databases lack the searching sophistication of ERIC or PsycINFO.