In 1905, in the British Journal Psychology, W. H. R. Rivers made some observations on senses of the Toda people. Rivers used the Muller-Lyer Illusion to look at the ability of the Toda to be able to describe illusions.
The Toda must be among the most interesting people living today. The current Wikipedia article is very well written – and is presented in a style that may well invite further research. There are usually about 700 Toda living in Southern India. The families attracted attention because of their uniqueness and their isolation. I can remember reading about the Toda years ago – well before Wikipedia came along.
The work by Rivers on the illusion came to mind yesterday as we were struggling with a rather esoteric series of non verbal reasoning exercises. In the Muller-Lyer illusion we are asked to work out if two lines are the same length – even though the arrows at the ends of the lines are pointing in different directions. One set of arrows, on one line, points inwards – and the other set, on the second line, point outwards. The whole point of the illusion is to work out if the equal lines, when laid beside each other, appear to be the same length.
These pesky non verbal reasoning questions were not clear – and the illustrator who designed them should possibly have looked at the work of Rivers, and others, before presenting them in a non verbal reasoning eleven plus book!