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In the Eye's Mind
Vision and the Helmholtz-Hering Controversy
By R. Steven Turner PRINCETON UNIVERSITY PRESS
Copyright © 1994 Princeton University Press
All rights reserved.
ISBN: 978-0-691-03397-6
CHAPTER 1
Introduction
THE EYE'S MIND
The strawberries went untended in Ewald Hering's garden during the summer of 1918. The old man was dead. He had remained active to the end of a long scientific career that had made him one of the most imposing figures in German physiology and also one of the discipline's most feared polemicists. Henng had cultivated the gardens of his scientific institutes with the same devotion and meticulous intensity he lavished upon the cadres of research students who passed through those institutes. Especially in the study of visual sensation and perception, he and his students had warred implacably against what they branded as the scientific orthodoxy of their day, and in so doing had inflamed one of the most notorious scientific controversies of the nineteenth century. The issues of the dispute had dictated the basic directions of vision research in Germany for almost forty years, yet few if any of them had been resolved at Hering's death.
The particular bitterness and the extravagant notoriety that surrounded this controversy sprang in part from the fact that Hering's chief opponent had been one of the most famous scientists of the nineteenth century. Hermann von Helmholtz (1821–94) had formulated the principle of the conservation of energy at age twenty-six, invented the ophthalmoscope at age thirty-one, and gone on to lay the foundations of modern physiological optics and acoustics in a series of monumental syntheses published in the 1850s and 1860s. He had then abandoned physiology for electrodynamics and finished his career as the doyen of German physics. Hering and Helmholtz had exchanged polemics directly in the 1860s, and thereafter Hering and his students warred with scientists they regarded as Helmholtz's disciples and surrogates, notably Adolf Fick, Arthur Konig, and Johannes von Kries.
Helmholtz, Hering, and their schools disagreed on many issues, chief among them being the proper sense in which the eye may be said to possess and to require a mind with which to see. On this issue they disputed the basis of the human capacity to visually perceive space and to localize objects in that visual space. Is this capacity innate and present at birth (the nativist position), or is it gradually acquired through learning and individual experience and mediated by inferential processes (the empiricist position)? The question of the eye's mind impinged upon the two schools' disagreement about the probable receptor mechanisms that underlie color vision. Do these consist of three mechanisms producing respectively the sensations of three fundamental colors, which are then psychologically mixed to produce the full range of color experience? Or do they consist of three sets of antagonistic receptors, producing respectively the sensations black-white, red-green, and yellow-blue? Can the eye's mind, in choosing among these alternatives, veridically assess the primitive or compound nature of its sensations? Do experience and inferential processes underlie the phenomena of contrast and adaptation, or are these produced by direct physiological mechanisms in the retina? These issues ramified into other lines of controversy: the interpretation of optical illusions, color constancy, eye movements, and adaptation; and the nature of retinal correspondence, with its implications for ophthalmological practice. The schools' antagonistic interpretations of all of these phenomena grew out of deep and divergent methodological commitments and ultimately out of disparate conceptions of the nature of life and of organic function.
Hering's death did not bring the dispute over these questions to an immediate end. His militant students kept the controversy alive for another decade, and textbooks preserved the memory of the dispute far longer, usually in pseudohistorical accounts served up for pedagogical or didactic purposes. Nevertheless, many contemporaries must have felt with relief that Hering's death had closed a chapter on an episode that had been uniquely unsettling among the scientific controversies of the nineteenth century. The persistence of the dispute, its pervasiveness, its resistance to compromise, the deep differences of methodological and philosophical principle that had divided its protagonists had challenged perceptions of scientific method and progress. By 1920 the controversy had already begun to pass into disrepute, ridiculed as scientific obscurantism par excellence and held up as a cautionary example against the uncontrolled proliferation of speculative theories.
Those same features make the history of the Helmholtz–Hering controversy a dramatic story and a revealing episode about the larger role of controversy in modern science. This book tells that story, from the initial confrontation of Helmholtz and Hering in the 1860s to the dissolution of Hering's school in the 1920s. Like the controversy itself, this narrative account of it sprawls across the history of a half-dozen academic disciplines over more than five decades and ramifies into accounts of many subproblems. Much, inevitably, has had to be neglected, and some arbitrary limits have been imposed upon the story in the interests of narrative cogency.
One of those limits is geographical and cultural. The account here deals almost exclusively with the Helmholtz–Hering controversy in Germany, where it began and was always most acute. The account largely ignores the reverberations of the dispute outside Central Europe, as it does the many developments in the larger science of vision that did not divide the two warring schools. The other limit is temporal. Despite the rhetoric of repudiation that was widespread after 1918, and despite the fact that the nature of the controversy changed decisively in the 1920s, the dispute itself has in one sense never ended. The broad issues of the Helmholtz–Hering controversy persist today and in some areas still structure the research front in problems of vision. That fact challenges both our conventions of historical narration and our understanding of how unresolved controversies affect the long-term development of science. This account touches upon these problems, but both lie outside its main focus on the decades from the 1860s to the 1920s.
THE STORY AND ITS THEMES
The narrative that follows opens with a general overview of vision studies in the two decades prior to the scientific debuts of Helmholtz and Hering. Chapter Two argues that the period between 1842 and 1867 marked a basic discontinuity in the venerable European tradition of vision research. Those years saw the creation of most of the new syntheses, methodologies, and integrating theories that were to dominate the field well into the twentieth century. Of course, the work of that period drew heavily upon past traditions and older research, but in consolidating and integrating them so successfully it simultaneously reduced them to largely historical interest. Helmholtz and Hering were two of the leading contributors to that midcentury integration of vision studies. Ironically their later dispute presupposed the elements of consensus which that integration generated; their controversy was to prove bitter and intractable in part because they agreed about so much.
The study goes on in Part Two to examine the careers, personalities, and programs of the two chief protagonists. It traces their initial clash over the issues of spatial and color perception, how their polemical exchanges mutually shaped the early development and presentation of their ideas, and how their competing ideas were received by contemporaries. Rhetorical analysis figures significantly in that discussion. Both protagonists were masters of the techniques of scientific argumentation, and they exploited those techniques consciously for programmatic ends. Rhetorical strategies included not only the usual forms of verbal argument, but also the visual and graphical techniques by which the two men represented concepts like color space and visual projections.
Those chapters insist, as historian Martin Rudwick has also done, on the "constitutive" nature of controversy in scientific change (Rudwick 1985). They contend that controversy does not act primarily in selectionist fashion to eliminate research programs and theoretical alternatives; it actively shapes outcomes. On this view, facts must be considered "controversy-laden" as well as "theory-laden"; theory itself may often be the product of tacit "negotiation" carried on as a crucial subtheme of polemical exchanges. Accordingly, the disputes between Helmholtz and Hering deeply shaped their own understanding and presentation of their respective scientific programs. Chapter Five argues in particular that the origins of the infamous nativist-empiricist controversy can only be understood fully in light of the respective programs and personal antagonisms of Helmholtz and Hering.
Part Three turns from the protagonists to their schools and traces the progress of the controversy from the late 1870s into the early twentieth century. It opens with a prosopographical examination of the most significant participants in the controversy and applies to the dispute the core set analysis advocated by Harry Collins and Martin Rudwick (Collins 1979, 1981,1985; Rudwick 1985). From the 1870s this controversy was above all else a dispute between scientific schools. The school structure strongly polarized the core set into two opposed groups of partisans. At least before the early twentieth century, only a few "nonaligned" contributors participated significantly in the dispute. Partisans of both schools courted these nonaligned participants very intensely, yet their small numbers limited their ability to influence, compromise, or moderate the debate.
Chapter Eight measures the schools of Helmholtz and Hering against the factors that determine the success of research schools, including leadership style, recruitment, and advancement of the sociodisciplinary interests of participants. It also emphasizes the role of what might be called "affective interests" in the dynamics of research schools: the ties of duty, fidelity, love, and inspiration that coexist alongside material and cognitive determinants. That kind of analysis is particularly crucial for understanding the academic world of nineteenth-century Germany, with its strong tradition of research schools, its powerful patriarchs, its hierarchical traditions, and the pervasive insecurity of the careers it afforded. The coherence and persistence of Hering's group in the face of substantial opposition especially reflect the real power of the emotional ties that sometimes bound members of a research group to the master and one another.
Subsequent chapters present the narrative history of the controversy, emphasizing the perception of light and color and the nativist-empiricist dispute. They exploit the long baseline of the controversy to trace how alliances within the core set altered, how the terms of the dispute underwent subtle changes of meaning, and above all, how the constellation of focal problems that constituted the dispute shifted over time. The most important of these shifts occurred in the 1890s, when the study of achromatic sensation replaced that of chromatic sensation and color blindness as the principal focus of dispute. Another shift, occurring at roughly the same period, was the growing appeal to clinical evidence and to the study of strabismus as arbiters in the dispute over spatial perception.
That discussion carries on the central theme of controversy as a constitutive element in scientific change. It demonstrates how polemical papers served a double purpose: that of refuting the opposition and winning the allegiance of outsiders, as well as that of negotiating potential compromises or terms of closure with the opposition. The two programs used controversy as a tool, and that tool in turn affected their mutual development. The duplicity theory of vision, the specific brightness of colors, the empirical horopter as the locus of apparent equidistance—all represented ideas introduced by one school or the other to serve specific strategic and polemical ends. All, however, fundamentally altered the research programs into which they were introduced in ways that the partisans scarcely foresaw.
Part Three concludes with two more analytical discussions. One of these introduces the notorious concept of incommensurability, which Thomas S. Kuhn believed should always attend episodes of deep change in science. Chapter Twelve argues that the Helmholtz–Hering controversy was rife with incommensurable perspectives, and that they can be traced on programmatic, perceptual, and linguistic levels. The last of these levels displayed Kuhnian incommensurability most vividly. Perhaps more than in any other scientific controversy of the century, this dispute was a struggle for semantic control, specifically in this case over the language in which visual experience would be described and analyzed. That discussion also contends that incommensurability can be strategic and deliberate. It can result from strategies of communication pursued by one or both parties to a controversy, and those strategies in turn from the sociodisciplinary interests of the group (Biagioli 1990).
That discussion also notes that incommensurability can adhere in the different ways in which competing groups of scientists bring together the different resources of objects, instruments, ideas, and persons in the day-to-day activity of investigating what are ostensibly the same problems. The schools of Helmholtz and Hering differed in the kinds of experiments that they performed and to which they gave most credence, in the forms of graphical and mathematical analysis they pursued, in the representations they gave of their results, and in the type of experimental subject they favored for study. The very instruments that they constructed reflected their different theories of human vision and in turn reinforced those differences.
Disciplinary interests and investments bore upon the Helmholtz–Hering controversy in ways that are analyzed in Chapter Thirteen. That controversy was fought out within the professionalized and bureaucratized framework of the German university system, and the parameters of that institutional world and the career paths it defined influenced the controversy at every turn. The dispute cut across several fields that were after 1850 just in the process of establishing themselves as institutionalized and autonomous disciplines. These included physiology, ophthalmology, and experimental psychology; physics, with a more venerable institutional tradition, was also a disciplinary center of vision research. The chapter discusses how Helmholtz, Hering, and their respective programs appealed to these various disciplinary perspectives and examines the changing involvement of these fields with the controversy and its central issues.
Historians' accounts of scientific controversies deal on the one hand with the men and women who conduct scientific disputes: their interests, institutions, compulsions, visions of nature, and their own consciousness of their enterprise. On the other hand these accounts also treat the theoretical ideas in dispute, and these can acquire an autonomous and historically legitimate existence apart from the personalities that created and shaped them. They come to be preserved in textbook accounts and in the collective memory of the community; ideas that have been rejected or ignored at a cognitive level often retain a tacit embodiment in instruments, presuppositions, and research practices. The historian aims wherever possible at a seamless joining of these potentially separate accounts.
In the history of the Helmholtz–Hering controversy, that narrative join proves impossible to sustain much past 1930. As a school controversy or as one susceptible to core set analysis, the dispute was largely over by that date, even though few of the key issues had been resolved or compromised and little consensus had been achieved. But if the history of the dispute in one sense had closed by 1930, in another sense it had just begun. The perspectives formerly represented by the two schools continued to inform the practice of vision research deep into the twentieth century, and in the 1950s and 1960s many of the original terms of the dispute seemed vehemently to reassert themselves. The story of the controversy, which (on this telling) has such a decisive beginning at the middle of the nineteenth century, threatens to have no single, unambiguous ending at all in the twentieth. Chapter Fourteen looks briefly at the survival of the issues of the dispute after 1930 and their place in the international study of vision. It suggests that within the framework of the historical evidence and the conventions of narration, several different endings might legitimately be applied to the story of the Helmholtz–Hering controversy. Each possible ending affords a subtly different perspective on the narrative significance of this account of the eye's mind and the rivalries among those who struggled to comprehend it.
(Continues...)
Excerpted from In the Eye's Mind by R. Steven Turner. Copyright © 1994 Princeton University Press. Excerpted by permission of PRINCETON UNIVERSITY PRESS.
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