Onder, A., A. Balaban Dagal, G. Ilci Kusmus, H. Bilici, H. Ozdemir, and Z. Kaya Deger. “An Investigation of Visual Perception Levels of Pre-School Children in Terms of Different Variables”. International Online Journal of Education and Teaching, vol. 6, no. 1, Jan. 2019, pp. 190-03, https://iojet.org/index.php/IOJET/article/view/384.