Howard E. Gruber

Moon Illusion and Emmert's Law.

The perceived size of an afterimage varies with the part of the sky to which it is projected in a manner predictable from Emmerts Law and the appearance of the sky as a flattened dome. This effect is directly analogous to the moon illusion.

Moon Illusion: An Event in Imaginary Space

The illusion was obtained with artificial moons viewed against a luminous ceiling, and also with an imaginary ceiling induced by first showing a luminous ceiling and then removing it before the moons were introduced.

Item Analysis and the Measurement of Change

THE PROBLEM of item selection is complicated by the fact that each item*will change in difficulty by some unknown amount as time elapses. If no ad ditional training is given, the item will probably in crease in difficulty as forgetting proceeds. If ad ditional training is given, as is typically the case with students taking the firstsemester of a one-year introductory course, some items may conceivably decrease in difficulty. In either case, the amount of change is unknown, and, indeed, sometimes the direction of change, making it difficult to apply ra tional techniques of item selection. The measurement of retention is particularly sensitive to the difficulty of the task or item; if the task is too difficult, performance may by uniformly low, in which case, differences between groups will be masked. In laboratory experime ntal work on learning, the savings method in relearning provides the most sensitive measure of retention and has been generally adopted wherever macimal sensitiv ity is desired. Several writers (e.g., Cronbachand Warrington (1), Guilford (2), Gulliksen (3), and Lord (4) , have dealt with the relation between the ability of the group tested and the difficulty of the items to be used in constructing a sensitive test. Lord (4), for example, points out that a tes t with maximal dis criminative power for examinees at a given ability level should have all items of the same diffic ulty, such that half of the examinees at the given ability level will pass the item and half will fail it. In a test-retest study designed to measure course reten tion, we may consider that we are comparing test performance at two levels of ability: before and af ter forgetting. Therefore, knowledge of the dis criminative power of an item in the initial test pro vides no clear indication of its discriminative power in the re-test, unless the amount of forgetting (i. e., the new ability level) is known in advance. But, of course, the amount of forgetting is exactly what we are trying to find out. This problem arose during an experimental com parison of two methods of teaching general psychol ogy?a conventional course with three class meet ings per week and a self-directed study course with about one class meeting per week. It was desired to measure retention of course materials a f t er an interval of 15 months, a situation in which, unfor tunately, retention may be expected to be low and the importance of the sensitivity of the instrument looms large. Having no basis for a rational selection of items at an optimal difficulty or discrimination level, it was decided to construct the test in such a way as to provide some information for future experiments of this kind. This approach had the advantage of hedging our bets. By using items of varying but known discriminative power and difficulty in the pre-test, it appeared moderately certain that some of them would be useful in the post-test. The present report deals, therefore, with two hypotheses: 1. Items that shift in difficulty toward the opti mal level of difficulty will become more discrimin ating with the passage of time, and items that shift away from the optimal level of difficulty will become less discriminating. 2. In a situation where forgetting occurs, items that were initially much easier than the optimal dif ficulty level will shift toward the optimal level and will consequently have greater discriminative pow er in the re-test than items that were initially clos er to the optimum in difficulty. The first hypothesis is more general, but has the limitation that it cannot serve as the basis for item selection until the re-test has been administer ed. The second hypothesis requires an assumption about the direction of change in ability in the popu lation being tested, and with that restriction it can provide a guide to the selection of items for the re test on the basis of initial test results.

Love, death, and continuity in Darwin's thinking.

The interplay among Darwins organizations of purpose, affect, and knowledge is examined, with particular focus on the development of his ideas about psychology. This enterprise was subordinate to his major enterprise, developing a clear and convincing theory of evolution. There is, nevertheless, a remarkably rich record available for reconstructing Darwins thinking in this domain. The historical context in which his ideas were constructed reveals the complex process of exchange that occurs between the individual and his or her intellectual milieu. Two examples of Darwins borrowing of ideas—from Lamarck and from Malthus are addressed. What emerges is that “influence” is not a passive copying. For an idea to be assimilated to a new intellectual organization it must be uprooted and transplanted, abstracted and transformed, and carefully worked into the structure of the new argument.

THE FORTUNES OF A BASIC DARWINIAN IDEA: CHANCE

A scientific theory is a much denser structure than is generally recognized. Almost every component idea is itself an intricate structure; and the whole is a complex of interacting parts. In constructing the theory of evolution through natural selection, Darwin made use of a number of images or metaphors: tree of nature, war, wedges, artificial selection, tangled bank, and contrivance. Each of these has a specific function in illuminating a part of the theory. These images are not merely didactic or communicative devices, they seem to play a role in the actual generation of the theory: there is probably a complex and lively interaction between different levels of experience, such as the conceptual and the imaginal. From a historical point of view, as one theory is assimilated by another, the earlier is necessarily distorted and only partially represented in the latter. As a consequence of this complexity, although some Darwinian ideas have been assimilated into psychological theories, one basic conception has been neglected. There is in the Origin of Species only one diagram. It represents Darwin’s idea that in the panorama of nature “organized beings represent a tree irregularly branched,” as he wrote in a notebook in 1837.’ This was 15 months before he formulated the theory of evolution through natural selection. Darwin used this metaphor in many theoretically productive ways. Yet this conception of fundamental irregularity in nature remains foreign to psychology and other social sciences, still dominated by a largely Newtonian world view. Some still-unexploited implications of Darwin’s metaphor have a bearing on the role of the individual in history and on the virtues of “weak theory.” In discussions of the philosophy of science it has grown commonplace to distinguish between the problem of justification, and the problem of discovery. The latter can be further subdivided into procedural and substantive issues. This leaves us with a tripartite division: how to know if a proposition, once uttered or formulated, is true; how to go about looking for propositions worth considering; and what sort of thing to look for. Within the context of discovery, something has been said about procedural matters. For example, writers in the vein of Peirce and Hanson focus on the method of retroduction; writers in the vein of Polanyi stress intuitive and nonrational aspects of the process of discovery. But substantive matters-what to look for?-have received much less attention. In an older philosophical tradition, discussions of the nature of matter, objects, space, time, life, intellect, morals, humanity, and society were not considered matters for specialists in “other” disciplines, but were part of a widespread

Darwin on Man: A Psychological Study of Scientific Creativity

HOWARD E. GRUBER, Darwin on man. A psychological study ofscientific creativity, together with Darwins early and unpublished notebooks, transcribed and annotated by Paul H. Barrett, London, Wildwood House, 1974, 8vo,. pp. xxv, 495, illus., £5.00. In the first part (pp. 1-257), Professor Gruber, a developmental psychologist and follower of Piaget who provides a forward, analyses the way in which Darwin gradually assembled his theory of evolution by natural selection. The second part contains mainly the notes that Darwin recorded concerning man and his relationship with other animals, and on mind, emotions and free will. The background to the period when Darwin was amassing his data (1838-1859) is dealt with, for a knowledge of it is essential if the novelty of his idea is to be appreciated. At a timewhenman was thought to be the Creators prize product, quite separate from animals, and when the materialistic approach to human brain function was unacceptable, Darwin was continually concerned with including man in his scheme. Other influences on him, from parents and teachers, are discussed, but Professor Grubers main task is to show how a genius takes a mass of evidence, theories, ideas, suppositions, and welds them into a biological law. Here we learn not only about Darwin, but the attributes of genius in general, and the methods of scientific thought. The original thinker uses stored, previously obtained evidence and insights, each in different contexts. He can discard or modify his ideas ruthlessly and is, therefore, never enslaved by them. He has an infinite capacity for taking pains and he has the ability clearly to maintain in his mind a variety of ideas, isolated one from the other and yet immediately available for comparative enterprises, and all constantly ready to be incorporated into the overall model. Such was Darwins mode of thought. The only possible criticism of this impressive study is that more consideration could have been given to Darwins psychoneurosis, which itself had an important role to play in his creativity by protecting him from society and so allowing him to give all his attention to his studies. It may be that the long delay in publishing On the origin of species was a direct result of it: anxiety and fear evoked by the possibility of a public reaction to a revolutionary notion that would bring upon him condemnation and ridicule. Darwins notebooks make fascinating reading and they constantly remind one of Harveys Praelectiones. Each was acutely aware of the world about him and would record any fact that seemed at the time to add to a corpus of knowledge necessary to establish, confirm, and sustain his biological concepts. The long delay between revelation and publication is also strikingly similar. A detailed comparative study may prove to be a rewarding exercise, and a contribution to the anatomy of genius; but on the other hand Darwin presents observations on sociological issues which Harvey does not. Professors Gruber and Barrett have produced an important book which will appeal to a variety of readers: biologists, psychologists, historians of science and medicine, philosophers of science, sociologists, and theologians. It can be warmly recommended, and at the price it is a bargain.