When there are articles or videos related to the one you are viewing, you will see a related papers icon next to the title, like this: 
For example:
Click on it and you will see a bibliographic list of papers that are related (including the current one). Related papers may be papers which are commentaries, responses to commentaries, erratum, and videos discussing the paper. Since they are not part of the original source material, they are added by PEP editorial staff, and may not be marked as such in every possible case.