Perspectives in Open Spaces: A Geometrical Application of the Thouless Index

A geometrical model for computing 'general perspectives' is discussed. It is based on the power function r = p(d/t) 1 -i, where i is the Thouless index for the phenomenal regression to the real object, r is the real size of the object, p is the apparent size, d is the distance between the subject and the object, and t is the distance between the subject and the projection plane. This model assumes that i is invariant for different distances and this was verified in seventy children and adults at distances of 15 or 120 m. A computer program draws families of curved perspectives which are well-fitted to the actual shape of large visual alleys produced by experiment in open fields.