APA PsycINFO includes many ways to refine your search, right on the front page. Scroll down to find them! Here are some recommendations
Other limiters that appear after you've done your search that are also useful
There are two types of subject headings in PsycINFO:
Subject: Major Heading - the primary tag for the article. Kind of like a precision strike.
Subject - includes all tags, including the major heading. A way to view the entire landscape of your topic in order to discover hidden gems.