Letters

Leoiiardo, Vol. 9, pp. 86-88. Pergamon Press 1976. Printed in Great Britain LETTERS Readers’ coiiiiiieiits are rvelcoiiied oii rexts priblislied iii Leonardo. The Edirors reserve the right ro shorten letters $or reasoiis of space. Letters shoirlrl be writferiiii English or in Freircli. ON RONCHI’S ‘NEW OPTICS’ (corit.) I wish to comment on the exchange of letters between James J. Gibson [Leoiiardo 7 , 382 (1974)l and Vasco Ronchi [Leoiiardo8,91(1975)] that arose from the publication of Ronchi’s article ‘Perspective Based on a New Optics’ [Leonardo 7, 219 (1974)]. The discussion involves two hypotheses of visual perception, which I shall refer to as Ronchi’s ‘new’ optics and Gibson’s ‘ecological’ optics. Since the clash between the two hypotheses is very recent, whereas the studies of the two authors go back several decades, Gibson’s opinion, according to which Ronchi‘s ‘new’ optics is deeply and seriously wrong, seems to me to be rather hasty. Ronchi’s ‘new’ optics is a synthesis of theoretical criticism and experimental work that he has carried out over a period of 50 years and of related work by collaborators at his National Institute of Optics at Florence, Italy. His hypothesis is capable of explaining a large number of optical phenomena. I shall mention four of them that I do not find explicable by Gibson’s ‘ecological’ optics. This may be due to my scanty knowledge of Gibson’s hypothesis, which is based on publications of his that I have been able to obtain. The optical phenomena are the following: The phenomenon of the persistence of retinal images or of afterimages is well known. Nine centuries ago the Arab Ibn-Al-Haitham (or Alhazen) used this phenomenon to conclude that vision must be brought about by an external agent, that is, by a luminous or illuminated object. For example, if an observer looks at the Sun and then shuts his eyes or enters a dark room, he will continue to ‘see’ the solar disk as a less bright afterimage not in the color of the Sun, but very close to the complementary color, for up to several minutes. Furthermore , if the observer turns his head or only moves his eyes, the afterimage appears to move in space, independently of the location of the Sun. If the observer has a strong afterimage, while it persists he will not be able to see objects within the afterimage. This means that the corresponding area on the retina of the eye has become insensitive to a further input of light from external objects. (2). The vitreous humor of the eye contains particles that may be seen to move about irregularly. These are called ‘flying gnats’. (3). If one receives a blow on the head or on an eye, one may ‘see’ a number of flashes, one ‘sees stars’. (4). The results of experiments with glasses that cause a viewer to see the external world upside-down show that, after about a week of wearing them, he will see the world right-side up. When the glasses are removed, he again will see the world upside-down, but within a day or two the world will ‘right’ itself. These phenomena, among many others, can be understood in terms of Ronchi’s ‘new’ optics. Can Gibson also provide an understanding of them by means of his ‘ecological’ optics? [cf. J. J. Gibson’s letter on p. 87.1 Leonello Boni 20 Via dei Pivieri 00169 - Rorne, Italy (1). FROM CONTRAST TO ASSIMILATION: IN ART AND IN THE EYE (cont.) With respect to the article by Dorothea Jameson and Leo M. Hurvich [Leoitardo 7, 125(1975)], I would like to make the following comments. What continually bothers me is that so many psychologists of perception and artists who deal with contrast phenomena ignore or avoid reference to the work of the French chemist M. E. Chevreul (1786-1889), who dealt with the effectsover a century ago in fine detail. Chevreul’s work, The Principles of Hariiioiiy arid Contrast of Colors (1839), is a rare masterpiece in the literature on color. It was translated into English and remained in print for 25 years. While Josef Albers in his book Iiiteraction...