Strength and limitations of the study
The main strength of the present study was its study design (placebo controlled, within subject studies). It investigated the potential effects of d-amphetamine and caffeine on SWM and VWM performance using SST and DST at different delay conditions. This study used d-amphetamine at a moderate-high dose (~33 mg), about two to three times higher than that used in most previous challenge studies. There are, however, limitations to be considered for future studies. First, the major limitation is the sample size; confidence would be increased with a larger sample size. Importantly, the sample size of female participants should be increased to identify sex-dependent effects as ovarian hormone may influence drug response [