Review: Perceiving Events and Objects, Language, Music and Mind

Abstract

This book is based on the proceedings of a symposium held in Uppsala in 1991 to celebrate Gunnar Johansson's eightieth birthday. The editors' aim was to avoid the common Festschrift form in which contributors review their own recent work, and instead to produce a volume critically exploring Johansson's research. They have succeeded in this aim, and have adopted a novel and interesting format to achieve it. The book begins with a conversation with Johansson in which the editors, who are all former students and colleagues, draw out the history of his research. The technique provides an excellent way of capturing the fine texture of a research career, and the transcript is skilfully edited and entertaining to read. Next comes a series of well-chosen landmark papers selected from Johansson's publications. These report experiments on vector analysis, depth from motion, biological motion displays, and self motion, and also include exchanges with James Gibson on theoretical issues. Most of the original sources are easily available, with one exception, which has particular historical interest. This is an edited version of Johansson's doctoral thesis, originally published in 1950, which describes a beautiful series of experiments using motion displays. They begin by extending the Gestalt law of Common Fate to motion and then go on to establish that patterns of moving dots are seen not as collections of individual motions, but as common and residual motions within the whole pattern, as if the visual system performs a vector analysis. Johansson captures very neatly the style of these experiments when he describes his research method as a "successive addressing of open questions to nature" (page 6). It is interesting to see that the advance beyond Gestalt findings which led to these important discoveries was made possible by Johansson's technical expertise in creating the entirely novel motion displays needed, combined with his inspiration in recognising their relevance to theoretical problems. This is illustrated especially well early in the thesis when Johansson writes about watching the motion of a tree blown by the wind, and describes how "the motion has at the same time a uniting and a segregating effect" (page 35). An interesting theme which emerges later in this section of the book is the development of the relationship between Johansson's thinking and that of Gibson. Their exchanges reveal some intriguing differences; Johansson's scientific creativity is always closely focused on experimentally tractable issues, and disciplined by experimental findings, whereas Gibson's equally creative thinking ranges more widely, but at times leads to vaguer and less consistent conclusions. In the last of the selected papers, written with Borjesson in 1989, Johansson's 'optic-sphere' theory moves more closely towards a Gibsonian 'direct' account of perception than does any of his earlier work. The theory proposes a description of the light reaching an eye in terms of a particular kind of projective geometry, in which distal propert...