Deformation of visual space at the ECVP in Groningen

Abstract

There is a fair amount of experimental evidence that what is visually perceived as being parallel in the world can be far from physically parallel (eg Blumenfeld 1913; Indow and Watanabe 1984a, 1984b; Cuijpers et al 2000). This experimental evidence, however, is usually obtained under rather contrived circumstances. Use is often made of faint lumi- nous lights in an otherwise dark room (Blumenfeld 1913; Indow and Watanabe 1984a, 1984b), or, in the cases of Cuijpers et al (2000) and Indow and Watanabe (1984b), of a restricted view in which ceiling and floor are concealed and the walls are covered with black wrinkled plastic sheeting or paper in order to prevent the subject from using environmental cues. In these experiments the deviations from veridicality can be quite substantial but even so an often recurring question is why these effects are of interest since one does not encounter them in daily life. One remark that can then be made is that some outdoor studies also showed a discrepancy between visual space and phys- ical space (eg Battro et al 1976, 1978; Wagner 1985; Koenderink et al 2000), although it should be noted that most of these experiments did not address parallelity directly. Fortunately, last year's ECVP in Groningen provided us with the ideal and appropriate circumstances to observe the phenomenon under `natural' viewing conditions.