Part V  Factors that triggered the paradigm shifts in the development of the duplicity theory

In retrospect, it can be seen that all the classical theories in vision research with the exception of Hering’s opponent colour theory were instigated by what may be termed observational facts. The theories of Newton (1671/1672) about light and colour, for instance, were triggered by his observation that the prismatic solar spectrum was rectangular in form.

Accepting the laws of refraction, he had expected the form to be circular. Yet, comparing the length of the spectrum with its breadth, he found to his surprise that it was about five times greater. He also found the two sides of the rectangle to be straight lines and the ends to be semicircular. It is important to note that Newton’s observations did not result from an attempt to confirm or falsify the refraction laws. Instead, the observations were made quite accidentally.

To explain his observations, Newton initiated a series of experiments, testing various hypotheses and soon reached the famous conclusion that white sunlight was compounded of an ­innumerable number of different rays and that the colours of the prismatic spectrum were original and connate properties of these rays – all in sharp contrast to the generally held view that the colours of the spectrum were qualifications of the white homogeneous sunlight caused by prismatic refraction.

Schultze’s duplicity theory was also based on observational facts. Thus, he arrived at his theory by combining two different sets of data. (1) Diurnal and nocturnal animals tended to have retinas dominated, respectively, by cone and rod receptors. In fact, some diurnal species had only cones and some nocturnal species only rods in their retina. (2) Night vision was achromatic.

196 factors that triggered the paradigm shifts

Apparently, these facts were derived mainly from his own painstaking histological studies and Aubert’s (1865) demonstration­ that saturation of colours deteriorated during long-term dark adaptation­ . Conclusive evidence that only rod receptors function in night vision was later provided by König (1894), who demonstrated that the spectral absorption of the photopigment of rods (rhodopsin) closely coincided with the spectral sensitivity of the human eye in night vision.

Perhaps the best illustration of how an observation may trigger a paradigm shift, though, was the unexpected discovery by Boll (1877) that the photopigment rhodopsin in the outer segment of the rods bleached in light and regenerated in darkness. Boll soon understood that rhodopsin had to play an important role in visual processing and therefore started an investigation of its photochemical reactions to reveal its secrets. This research was quickly followed up by Kühne who, during an intense research period (1877–1882), arrived at his general photochemical theory of vision, where phototransduction both in rods and cones was explained in photochemical terms. Accordingly, he postulated the existence of photopigments, not yet measurable, in the cones. In fact, he suggested that even rods in the light-adapted state, where rhodopsin was substantially bleached, contained undiscovered, visually active photopigments.

The trichromatic colour theory was also instigated by an observational fact. Thus, the trichromatic colour theories of Lomonosow, Palmer and Young were all based on the old and well-known fact that three different pigments mixed in various proportions were sufficient to produce all object colours. This fact, however, did not bear much weight, since, as Newton (1730) and later Helmholtz (1852) had made clear, the colour produced by pigment mixing depended on a subtractive mixture procedure making it impossible to control the kind of rays that struck the retina. Also, Helmholtz (1852) found that adding three spectral lights could not produce all spectral colours, and

factors that triggered the paradigm shifts 197

that at least five different primary retinal processes had to be postulated in order to account for human colour vision.

For a long period of time, then, the trichromatic colour theory was a speculative theory without any firm foundation. Eventually, however, a firm basis for the trichromatic theory was provided by Maxwell (1855, 1860). Taking advantage of Newton’s principle of gravitation, he demonstrated, in opposition to Helmholtz, that three primary lights were, in fact, sufficient to match every spectral colour. Furthermore, in support of the trichromatic colour theory he demonstrated that protanopes had a reduced form of colour vision in that they lacked the ‘red’ receptor system.

In contrast to these four classical theories, Hering’s (1878) opponent colour theory was not triggered by facts, but by ideas, i.e. by Spinoza’s famous doctrine of psychophysical parallelism as applied to vision by Mach (1865). Thus, Hering immediately embraced Mach’s psychophysical maxims and made them both the starting point and basic presumption on which his deductions about brain activities could be made.

Yet, it is important to note that the psychophysical maxims of Mach only represented the tool whereby the opponent colour theory could be built – they did not form any part of the theory per se. Thus, to develop his theory, Hering also needed an analysis of the colour phenomena. Here he could take advantage of Goethe’s colour theory – especially Goethe’s famous colour circle where primary colour qualities and opponent interactions could be found. The development of the opponent colour theory in detail and his strong conviction that his theory was correct were, however, first and foremost based on his own painstaking and keen phenomenological analysis as regards colour mixing, successive and simultaneous colour contrast, and also successive and simultaneous colour induction.

Given these important features of the development of the duplicity theory, the question naturally arises as to whether they

198factors that triggered the paradigm shifts

are representative of scientific progress in general. An answer to this question presupposes knowledge about this progress – which has been mainly explored within the philosophy of science. The ­contributions of Popper and Kuhn have become classic (for an ­evaluation see Chalmers, 1986).

28  Summary of K. R. Popper’s and T. S. Kuhn’s models of scientific development

Although scientific theories and laws of nature may never be proved in any definite way by induction, as Hume had made clear, Popper (1969, 1975, 1994) pointed out that they may be falsified on the basis of empirical evidence and purely deductive reasoning, i.e. the modus tollens deduction form of classical logic (see Popper, 1975, pp. 75–77). Hence, he assumed that scientific theories could be tested by attempts to refute them, and by selecting the most successful theories that withstood severe falsification tests, Popper believed that science could progress ever closer to, but never reach, the ultimate truth. The key to scientific development, therefore, according to Popper, was not the collection of observational statements, but the emergence of competing, falsifiable theories. Only by searching for falsification of theories and, on this basis, selecting the most successful ones, could science hope to learn and advance.

Popper’s view of scientific progress may be summarized as follows: progress starts when a theory is refuted or falsified. This will create a problem for the relevant scientific community. In order to solve the problem other falsifiable theories are proposed. These new theories are then criticized and tested. As a result one or a few of the theories will prove more successful than the others, i.e. they may withstand severe falsification tests, may have greater empirical information or content, may be logically consistent, may have greater explanatory and predictive power, and may be more simple. Eventually, however, even the most successful theory will be falsified. When this happens, a new serious problem has emerged which calls for the invention of new falsifiable theories followed by renewed rational critique and testing – and so on, indefinitely, since the ultimate truth can only be approached but never reached.

200 factors that triggered the paradigm shifts

Popper (1969, pp. 406–407) presented his view in the following simplified diagram:

P1 → TT → EE → P2

where P1 is a first problem, TT the tentative theories that are offered to solve P1, EE the elimination process where the theories are exposed to falsification tests, and P2 the new problem which emerges from the exposed errors of TT. New theories have then to be found to solve P2 and so on indefinitely.

The account provided by Kuhn is quite different (see Kuhn, 1970, 1994). He sees scientific development not as characterized by a succession of falsifications, but by a succession of traditions, i.e. periods of normal scientific activities punctuated by revolutionary alterations.

His vision of the way science progresses may be summarized in bare outlines as follows: the pre-scientific period is characterized­

by disagreement and constant debate over fundamentals, like basic problems to be solved, methods, results and theories, making it impossible to get down to detailed scientific work. Eventually, however, this disorganization becomes structured and directed when a single paradigm, i.e. a theoretical framework or ’disciplinary matrix’, is adhered to by a scientific community. The paradigm guides the scientists with regard to basic questions, methods and hypotheses that should be adopted. In this first ‘normal’ scientific period, scientists articulate and develop the paradigm through painstaking and detailed experimental research. The scope of the scientific knowledge is thereby extended and the precision of the scientific statements sharpened, but the scientists do not aim at unexpected facts and new theories, and when successful, find none. To bear the burden of this esoteric and time consuming endeavour, the ‘normal scientist’ must be devoted and uncritical of the paradigm within which he works. Indeed, a failure to solve a problem in his research tends to be seen as a personal failure, rather than as an inadequacy of the paradigm. Fundamental anomalies in the fit

summary of k. r. popper’s and t. s. kuhn’s models 201

between nature and theory may be ignored, explained ad hoc to resolve the apparent conflict or set aside for future work, but do not lead to a ­renouncement of the paradigm.

Sooner or later, however, the paradigm becomes weakened and undermined by an increasing number of obvious anomalies. Some scientists may then begin to lose their confidence in the paradigm and may even openly express their discontent with it. More and more attention is devoted to the difficulties by more and more of the most eminent research workers in the relevant scientific community. Speculative and unarticulated theories that could point to ­fundamentally new discoveries may be developed. In fact, this period very much resembles the pre-scientific period. The time is now ripe for a revolution if an alternative paradigm not beset with obvious anomalies is available. Kuhn has likened the change-over from one paradigm to another to a conversion and a gestalt switch. Indeed, the choice of a new paradigm is seen as a decision to adopt a different native language and to develop it in a different world. The development, therefore, is not a progress toward an ultimate truth.

Scientists embrace a new paradigm for all sorts of reasons depending upon idiosyncrasies of autobiography and personality and not primarily on logical considerations. Thus, the kind of factors that prove effective in causing scientists to change paradigm is mainly a matter to be discovered by psychological and sociological investigations,­ although logical arguments are involved such as numbers and the seriousness of the anomalies.

The scientific revolution is over and ‘normal science’ can continue when the relevant scientific community as a whole has abandoned the previous paradigm and adopted the alternative new one – leaving only a few dissenters who eventually die out. Kuhn sees the old and new paradigm as ‘incommensurable’. Thus, there are no plain logical arguments that demonstrate the superiority of the successful paradigm, since the fundamental premises of the two

202factors that triggered the paradigm shifts

paradigms are different. The decision to change paradigms depends in the last instance on the importance given to a variety of values, often in conflict, by individual scientists. The possibility of solving new puzzles that may please their institutions and promote their career may have a strong impact. No specific plan guiding the scientific development is apparent and no ultimate truth is approached.

29  The development of the duplicity theory as a test of Popper’s and Kuhn’s models

It is apparent that neither of these models fit well with our ­description of the development of the duplicity theory. As regards Popper’s model, none of the classical theories of Newton, Young, Schultze, Kühne and Hering was triggered by an attempt to falsify or refute current hypotheses or theories. Newton’s starting point was the rectangular form of the prismatic solar spectrum he observed when he looked at its beautiful colours; Young based his theory on the old and well-known fact that three pigments were sufficient to produce every object colour; Schultze reflected on the fact that nocturnal anddiurnal animals tended to have rodand cone-dominated retinas, respectively, and that colours were absent in night vision; Kühne’s theory was instigated by the great discovery of Boll that rhodopsin bleached in light and regenerated in the dark; and Hering was spurred on by Mach’s psychophysical maxim. Thus, there is little evidence of long, fruitful falsification periods ending with falsification of the most successful hypothesis and the development of a new, better one triggered by this last falsification.

It is evident that Maxwell (1855, 1860) provided conclusive evidence in support of Young’s trichromatic colour theory by demonstrating that three standard spectral lights were sufficient to produce all spectral colours, but his experiments represented a confirmation of an already existing theory and not a falsification. It should also be noted that Young’s theory was immediately accepted by the relevant scientific community without much debate following the discoveries of Maxwell.

Interestingly, the spectro-photometric measurements of Marks et al. (1964) and Brown & Wald (1964) that demonstrated the

204factors that triggered the paradigm shifts

existence of three different cone photopigments situated in different cones have resulted in a transformation of the basic assumption of Young’s colour theory from a theoretical to a factual status. There is, of course, no room for such a transformation in Popper’s model.

Our description of the development of the duplicity theory is not easily reconciled with Kuhn’s model either. Thus, in apparent contrast to Kuhn’s account of scientific progress, the development of the duplicity theory has been marked by a series of important steps that all still are regarded as milestones in our understanding of visual phenomena. In fact, no so-called crises and revolutions, where one paradigm is abandoned and another adopted, are apparent. Instead, the steps taken appear to complement each other and may therefore exist simultaneously. Of course, an understanding of Kuhn’s model depends to a large extent on how the concept ‘paradigm’ is interpreted. Yet, even if it is asserted that there has been no paradigm shift in vision research since Newton, one would have to admit that great discoveries and large progressive steps in the development of the duplicity theory have occurred and that, therefore, his characteristics of so-called ‘normal science’ would not be met. Also, the sharp differences in opinion between Hecht, Wald, Rushton, Barlow and Lamb in the twentieth century, where relatively little fundamental change has occurred in the development of the duplicity theory (and on these grounds might be characterized as a ‘normal’ scientific period), are not in accord with Kuhn’s description where he emphasizes an uncritical and devoted attitude toward the ruling paradigm. Instead, the leading authorities have attempted to build their own theories on rational grounds, mainly in conflict with each other. Similar considerations apply for the period between Newton and Young.

Moreover, there is at present no indication that a single paradigm will emerge and dominate vision research. Contrary to this view, the scientific progress in vision research appears to move simultaneously in several different directions, focusing on visual processing at various

the development of the duplicity theory 205

stages between the retina and the central brain areas, on normal and abnormal processing, genetic problems and visual processing in different species. Thus, the number of subjects appears to increase with a continuing proliferation of scientific specialties, giving the impression that the scientific progress is diverging, not converging. Certainly, there is, at present, no sign that vision research will settle on a common paradigm.

Yet, the best illustration of the failure of Kuhn’s model to provide an adequate account of the development of science, in general, is the paradigm shift from the presumptions of the Ancient Greeks (that the crystalline lens was the actual sense organ and that the information about the outer world was obtained by rays that emanated from the eye towards the object) to the conceptions of Kepler and Newton that the lens was just an optical focusing device and that light moved in the opposite direction. Obviously, this change in view is not merely a ‘conversion’ or a ‘different language developed in a different world’, but a change from false presumptions to assumptions that today are generally considered as facts.

As seen, Kuhn’s model, like Popper’s, gives no room for such a progressive change, also witnessed by the change in the status of Young’s trichromatic theory.

It is apparent that the models of Popper and Kuhn have left out some important factors involved in the development of scientific theories. Perhaps the most important weakness of the models is that they do not give any adequate account of how new theories arrive. In the development of the duplicity theory explorations and unexpected observations not based on attempts to falsify existing theories (Popper) or triggered by obvious anomalies (Kuhn) have played a crucial role.

The question has often been raised as to whether scientific progress is mainly a rational process as assumed by Popper or an irrational process as assumed by Kuhn. The development of the duplicity theory obviously favours the assumption of a rational process. Such a rational attitude is well illustrated in Helmholtz

206factors that triggered the paradigm shifts

(1867) where he abandoned his own hypothesis and immediately accepted Maxwell’s results and conclusions and, hence, the trichromatic colour theory.

Also, the dispute between the followers of Hering and Helmholtz was soon settled in a fruitful and rational way by the assumption that the Young-Maxwell-Helmholtz colour theory applied to early phototransduction processing in the retina, while Hering’s theory applied to more central processing.

In fact, the hypothesis that the normal human retina contains three different kinds of cone, each with a different photopigment that absorbs light and, thereby, gives rise to a cascade of photochemical processes in the receptors that triggers neural processes, which at later stages in the visual pathway are transformed into opponent processing, is today generally accepted as a fact.

Thus, although Popper and Kuhn may be right in that science never will disclose the ultimate truth, scientific development entails the promising possibility that a theory may become attached to an increasing number of facts with increasing precision and ultimately be regarded as a fact in itself with important theoretical and practical implications.