How to re-use information that is itself a conclussion drawn from another source
It's definitely easy to get overwhelmed with all of the sources/papers available. I'm a graduate student and it still happens -- there's always lots to read and never the time to read it all.

Nevertheless, the proper thing to do here if you wish to cite the information in (Ververidis and Kotropoulos 2006) is to read that paper and use it. That doesn't mean you have to read it in-depth, but you should at least skim it. The same goes for other papers.

There's a couple of reasons for this:


Remember the point of a citation is to give credit where credit is due. That means you give credit to the original author, not someone who summarized their idea.
What's to say that the authors of the summary correctly summarized the idea? It's (generally) safer for you to go straight to the source.


A notable exception to this rule might be when reading a survey paper/book. These provide overviews of an entire domain -- if you're not actually exploring that domain in your own writing, the survey paper can be an acceptable way of citing an idea. That being said -- it's always preferable to cite the original source.