In 1962, Peal and Lambert published a study highlighting the importance of controlling for such factors as age, sex, and SES, as well as of having a standardized measure for bilingualism when selecting a sample of bilinguals to be studied. In their study they carefully matched bilingual to monolingual participants, and found that the bilinguals appeared to have significant advantages to that of their monolingual peers outperforming in both verbal and non-verbal tests, more specifically in the non-verbal tests. In continuation of this study, and studies alike, the literature after this point began to undergo a shift of focus erring more particularly into areas of cognitive development and aptitude such as: perception and executive functioning.