I see. So I will just accept that this study was carried out even though nobody can say they have actually read it. Enjoy the rest of the weekend everybody.
Just go to a University library with a psychology department and look it up. That’s what libraries are for, you know?!
People are so lazy nowadays. If it ain’t on-line, it “doesn’t exist” nowadays, in this lazy student’s era.
There is still a lot that has not been digitized yet, especially this kind of proceedings, and many monographs. If you only look for literature on-line, you are severely restricting yourself, and if you think something “doesn’t exist"because it isn’t on-line, you are fooling yourself. Lazy!
I should ad here that a quick on-line catalogue check of the University library here in Leiden reveals that the relevant proceedings series does exist and is present in the Leiden University library. I therefore see no reason to doubt that the paper quoted exists. Just look up the series in a library, as you should have done anyway. As it is an existing Proceedings series, I see, unlike you, no reason to feel the citation is “dubious”.
