Effects of indoor nature density and sex differences on working memory

The positive impact of nature on working memory is well established; however, the relationship between indoor nature density, sex, and working memory remains unclear. This study aimed to investigate the impact of indoor nature density on working memory and explore sex differences. Forty-one participants (26 females and 15 males) viewed 200 images of indoor environments with varying indoor nature densities. Following image viewing of each density group, participants completed a backward digit span task, and their electroencephalogram (EEG) was recorded during both image viewing and task performance. The results indicated that as indoor nature density grew, there were increasing trends in backward digit span scores and relative frontal theta during the task and decreasing trends in the frontal theta-to-alpha ratio (TAR), theta-to-beta ratio (TBR), and theta-to-gamma ratio (TGR). According to the post hoc results of relative frontal theta during the task, frontal TAR, and TGR, working memory might be optimized in 25–36% indoor vegetation density. The study also found significant sex differences: females showed more substantial improvements in working memory with increased exposure to indoor nature density than males. This study’s results provide evidence for practical guidelines of designing indoor environments that enhance working memory.