Pedugsorn, M., S. Vittayakorn, and P. Sudwan. “3 and 2 Dimensional Perception in the Mentally Retarded”. Journal of Associated Medical Sciences, vol. 26, no. 2, Mar. 2015, p. 61, https://he01.tci-thaijo.org/index.php/bulletinAMS/article/view/60462.