Research candidates are drawn by the WEIRD criterion

  most participants in psychological studies have been WEIRD, - drawn from societies that are Western, Educated, Industrialized, Rich, Democratic. 

Other premises of the argument pointed out that not only was this a very narrowly circumscribed sample population, it was also (a) an exotic outlier group, especially from an historical perspective, that was nevertheless (b) typically treated by researchers as representative of the species as a whole. Results from studies done with WEIRD participants (and typically by WEIRD cognitive scientists) were commonly extrapolated, taken to be true of human beings in general, and thus to be illuminating universal features of human psychological nature.