In 1963, Segall, Campbell and Herskovitz compared susceptibility to four different visual illusions in three population samples of Caucasians, twelve of Africans, and one from the Philippines. For the Müller-Lyer illusion, the mean fractional misperception of the length of the line segments varied from 1.4% to 20.3%. The three European-derived samples were the three most susceptible samples, while the San foragers of the Kalahari desert were the least susceptible.
In 1963 Segall, Campbell and Herskovitz compared susceptibility to four different visual illusions in three population samples of Caucasians, twelve of Africans, and one from the Philippines. For the Mülle.r-Lyer illusion, the mean fractional misperception of the length of the line segments varied from 14% to 20.3%. The three, European-derived samples were the three most susceptible samples, while the San foragers of the Kalahari desert were the least susceptible.