The Effect of Separation between Test and Comparison Objects on Size Constancy at Various Age-Levels

Abstract

The effect of separation between test and comparison stimuli on size constancy at various distances was determined for children and adults. Separation slightly reduced the tendency toward size constancy at the longer distances. The data are interpreted as supporting the assumption that size constancy and the Ponzo illusion share common mechanisms, since the developmental size-distance function is independent of whether the comparison is successive, as in most size-constancy experiments, or simultaneous, as in the Ponzo illusion. A number of investigators have suggested that size constancy and the Ponzo perspective illusion share common mechanisms.1 Specifically, it is assumed that one of the factors underlying size constancy is that subjects make depth inferences from converging lines, which are ordinarily associated with distance in the normal environment. When converging lines are presented in the twodimensional Ponzo figure, distance is falsely indicated, resulting in an inappropriate correction of the upper or 'more distant' line of the Ponzo figure. Evidence for this hypothesis is presented by the similar increase in both measures as a function of chronological age.2 Received for publication December 2, 1969. The research was supported by Grant MH-08061 from the National Institute of Mental Health. Dr. Brislin is now at Western Washington State College. 1 R. Tausch, Optische Tiiuschungen als artifizielle Effeckte der Gestaltungsprozesse von Groissenund Formenkonstanz in der naturlichen Raumwahrnehmung. Psychol. Forsch., 24, 1954, 299-348; E. von Holst, Aktive Leistungen der menschlichen Gesichtswahrnehmung, Stud. Gen., 10, 1957, R. L. Gregory, Eye and Brain, 1966, 145-156. 2H. W. Leibowitz and J. M. Judisch, The relation between age and the magnitude of the Ponzo illusion, this JOURNAL, 80, 1967, 105-109; H. W. Leibowitz, S. W. Pollard, and D. Dickson, Monocular and binocular size matching as a function of distance at various age levels, this JOURNAL, 80, 1967, 263-268.