Letters

Leonardo, Vol. 4, pp. 195-203. Pergamon Press 1971. Printed in Great Britain LETTERS Readers' comments are welcomed on articles published in Leonardo. In general, short letters stand best chance ofpublication. The Editors reserve the right to shorten letters for reasons of space. Letters should be written in English or in French. ON INFORMATION AVAILABLE IN PICTURES I feel greatly honoured by the editor's invitation to comment on Professor Gibson's paper in the Winter, 1971 issue of Leonardo, for there is no student of perception from whom I have learned more. In a more extensive discussion of his theories published elsewhere [1], I ventured to describe his account of the relation between perception and painting as a 'Copernican Revolution'. But Copernicus was not quite right and neither, I think, is Professor Gibson. I should like to take as my starting point his description of a photo-mural that permits an observer at the proper station point to 'perceive' the distance of one of the trees and its height while he still remains aware of the distance of the wall and I should like to begin by discussing the first of these observations. To what degree ofaccuracy could the distance and height be estimated? How was this accuracy tested? Assuming for argument's sake that the estimate was very good indeed, what other questions about the landscape represented in the photo-mural was Gibson's observer able to answer? Clearly, ifthe mural was black-and-white, questions about the colour of objects would have been inappropriate. But we may also ask up to what dist:lllce features were correctly interpreted? Were distant hills? Were trees silhouetted against the sky read correctly as a three-dimensional array? Were clouds seen at the correct distance and the correct shape? However pedantic and irritating these questions may sound, they must be asked if we are to establish first of all that the information provided by the picture was necessarily incomplete and that there are degrees of incompleteness. I think Professor Gibson and I are in agreement about this limitation of pictorial information. The next question now to be asked seems to me to concern the difference between such incomplete information and the one provided by a perfect duplication of the sheaves of light impinging on the retina when looking first at the real landscape and then at the reproduction through a peephole at proper distance. It is a fact established by projective geometry and mentioned by Professor Gibson that 195 the information content of the duplicate is still very far from perfect. There are many questions about the scenery 'out there' which we could not answer during such an inspection. In fact, it is only our knowledge of the 'ecology' of our normal environment that prevents such a view from collapsing into total indeterminacy. We know that the surfaces of lakes are level and that roads do not really converge into a point, that there is generally one source of light, the sun, which shines from above and accounts for the shadows, that walls are rarely tilted and that grass is more or less green so that the modifications of this colour may be due to light. But all this knowledge will not enable us to draw a completely accurate map of the landscape we perceive through the peephole. But granted that the information offered in either case is and remains incomplete, is there really such a tremendous gulf between the 'facsimile' landscape and the black and white photo-mural? In my book on Art and Illusion [2], I argued that there was not and that there was a gradual and continuous reduction of information content that led from the naturalistic view to a line drawing. Professor Gibson cannot accept this postulate of continuity because he is committed to the view that for an observer who is free to move as he wishes, the sight of the real scenery provides complete information about the visual array. Salutary as I have always found Professor Gibson's admiration for the achievement of visual perception, which has certainly been much underrated in the tradition that extends from Berkeley to Helmholtz, I still fail to see...