Size Constancy, Terry Pope’s Glasses, and the Moon Illusion

LCfJt?U/Y/O. VOI. 15. NO.3. pp. 205-207, 1982 Printed in Great Britain 0024-094X/82030205-03$03.00/0 Pcrgamon P r w 1 id SIZE CONSTANCY, TERRY POPE’S GLASSES, AND THE MOON ILLUSION David W. Brisson” Introduction I have been interested in stereoscopy in its various forms for a long time. As a child I remember very clearly the old stereopticon at my grandfather’s beach cottage with the slides, or rather ‘display cards’, of the Grand Canyon,groups of miners in front of a general store, etc. in miniature three-dimensions. It is the miniature quality of such scenes which interests me now, and which is the subject of this paper. While visiting the British artist Terry Pope at the University of Reading, I was fortunateenough to have him demonstrate some of his work with stereoscopy to me. One such demonstration involved the use of a pair of mirrored glasses which effectively widened the distance between the two eyes (Fig. 1); In other words, by the use of mirrors, very cleverly and beautifully constructed, Pope made it possible to view the world as though the two eyes were situated an inch or so farther apart than they actually are. Pope had not had clear responses from the many persons who had tried looking through these glasses, and for quite a long period while I looked through them, I was not sure exactly what was wrong, but I knew that there was something Fig. I. Two o f Terry Pope’s stereoscopic mirrored glasses. Top: Phantascope I, 1980, 33 x 12 x 10 cm. Bottom: Space enhancing. 1980. perspex, mirror. attuglass. ‘Artist and teacher(deceased),Box 85, Rehoboth,MA02769, U.S.A. (Received 11 May 1981) strange about the way things looked. Suddenly, I understood what it was. The world looked in every way normal, but everythinglooked very tiny. Everything was in correct relation to everything else, but everything was small. The coffee cup and the box of matches on the table were minute; likewise a pencil was the size of a tooth-pick. In every other aspect everything seemed right: there was no increase or decrease in the field of vision, no distortion of perspective or anything except a sense of uneasiness when I watched my hands as I picked things up or when things moved. This seemed a logical result by virtue of the effect of simply changing the amount of binocular disparity. Binoculars, of course, are constructed in the same way, but they are always constructed in conjunction with telescopic lenses. In this case there was no magnification of the images. It might be presumed that the mirrors increased the effective distance from the objects, and thus reduced the retinal image, which in fact they did, but not by a significant amount, at least not sufficient to produce the enormous effect that occurred. I was reminded of the effect of the stereopticon, which was very similar. Images through the stereopticon had always looked tiny to me in the same way, although the effect was hardly as powerful as in this case. The experience was also connected to the idea of size constancy, which is clearly a fundamental aspect of visual perception. This experience seemed to deny the principle of size constancy in a very serious way. By size constancy I mean the well-known perceptual principle that a change in the size of the retinal image of an object does not usually result in a sense of any change in the perceived size of the object. Here was a clear case where the object was perceived as altered in its perceived size without having changed its size on the retina. In fact, as these ‘miniature’ objects were moved about, they retained their perceived ‘miniature’ size. Thus, size constancy was preserved after all! Apparently, however, size constancy is not simply a function of the ‘known’ size of the object. I should add here, that although the world ‘looked’ little, at no time did I have any feeling that it actually was the size that it appeared to be. There was no anxiety associated with it at all, but on the contrary a...