Cognitive performance from infancy to adulthood in Japan from 1998–2001 to 2014–2019: A study using the Kyoto Scale of Psychological Development

Declines in cognitive performance have been observed in many Western countries in the 21st century, but it is still unclear whether similar declines are occurring in East Asian countries. We examined trends in cognitive performance over a 20-year period in Japan and analyzed how these trends varied from infancy to adulthood and between males and females. Data were collected between 1998 and 2001 (n = 2677; 49 % females) and 2014 and 2019 (n = 3243; 51 % females) using the Kyoto Scale of Psychological Development and analyzed using linear regression models. We found that cognitive performance had improved over the years for boys and girls aged 3 to 10 years old, with only minor changes observed at younger and older ages. Girls showed an advantage in cognitive development over boys from 1 to 3 years of age, while boys outperformed girls from 10 years of age into adulthood. We found suggestive evidence of slightly faster improvement in cognitive development over the years in boys compared to girls. These results were roughly similar for general cognitive development, cognitive-adaptive development, and language-social development. These findings suggest that the cognitive performance of Japanese children has continued to improve over the past two decades. Japan provides an example that the decline in cognitive performance observed in many industrialized countries in the 21st century is not inevitable.