City Research Online

Abstract

The illusion of apparent oscillation produced by a rotating trapezoidal object (generally known as Ames' window illusion) was investigated. Previous explanations of this phenomenon were reviewed, and found to be inadequate to relate all the different parameters of the illusion.

The trapezoidal stimulus was analysed in terms of the three main types of visual information that it provides: the speed of rotation; the surface pattern; and the continuous perspective transformation, projected onto the frontal plane. This transformation was considered in some detail, and it was found that it could be summarised by considering the elliptical loci produced by projection of the corner points of the trapezoid as it rotated. A computer program was produced to plot these loci for any particular trapezoid.

Hypotheses were proposed concerning the relative importance of these three main types of visual information. These were tested in a series of six experiments.

The results obtained in this study, and the published results of similar studies by others, were considered in detail. The data was analysed in terms of the different types of information investigated.

In general, the results supported the proposed hypotheses. Speed of rotation was found to have a significant effect on the type of motion (rotation or oscillation) seen; there was found to be a fundamental change in the nature of the illusion with speeds greater than 30 rpm. Surface pattern, however, was found to be relatively unimportant. But the most significant finding was that consideration of the projected transformation of the shapes used enabled the type of motion seen to be accurately predicted, by following a simple set of rules. This was found not only for the experiments reported here, but also for the published results of similar studies by others.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RE Ophthalmology
Departments:	School of Health & Medical Sciences > Department of Optometry & Visual Science School of Health & Medical Sciences > School of Health & Medical Sciences Doctoral Theses Doctoral Theses

Export

Downloads