A pervasive tendency for analogies to contribute to the development of entrenched misconceptions is identified. The misconceptions have the form of reducing complex new knowledge to the core of a source analogy. A taxonomy of ways that analogies induce conceptual error is presented, with examples of common biomedical misconceptions corresponding to each. In order to combat the tendency toward oversimplification associated with the use of a single analogy, an alternative approach involving integrated sets of multiple analogies is offered. In the multiple analogy approach, additional analogies are introduced that correctly convey information that is incorrectly represented (or not represented at all) in an earlier analogy. Thus, the pedagogical strengths of analogies are retained while their weaknesses are mitigated. The multiple analogy approach is illustrated by the example of force production by muscle fibers. The use of multiple analogy sets is made more tractable by the employment of composite images, with situation-dependent selective instantiation of aspects of the composite. Finally, the situation of analogy is argued to be one instance of a more general pattern of oversimplification-based misconception development attributable to the use of single knowledge sources when compilation of multiple sources would be more appropriate. MULTIPLE ANALOGIES FOR COMPLEX CONCEPTS; ANTIDOTES FOR ANALOGY-INDUCED MISCONCEPTION IN ADVANCED KNOWLEDGE ACQUISITIONFew would disagree that analogy is an important tool in the acquisition of new knowledge. Indeed, work in cognitive science and educational psychology in the last dozen years provides ample evidence of the usefulness of analogy in learning and has substantially advanced our understanding of the psychological mechanisms responsible for that utility (e.g., Burstein, 1983;Carbonell, 1983; Collins & Gentner, in press;Gentner, 1983;Gentner & Gentner, 1983;Gick & Holyoak, 1980;Rumelhart & Norman, 1981;Vosniadou & Ortony, 1983). Yet, as this paper will demonstrate, the use of analogies in learning is far from straightforward and surprisingly often results in deeply held erroneous knowledge.Our intention is to offer a more temporized and cautionary alternative to the general enthusiasm for learning by analogy, especially in its most common form: The use of a single mapping between a source and a target concept (the "topic")--what we will refer to as a "single analogy." (For exceptions that address more complex uses of analogy, see Burstein, 1983; Collins & Gentner, in press.) We argue that single analogies that help novices to gain a preliminary grasp of difficult, complex concepts may later become serious impediments to fuller and more correct understandings. Specifically, although single analogies rarely if ever form the basis for a full understanding of a newly encountered concept, there is nevertheless a powerful tendency for learners to continue to limit their understanding to just those aspects of the new concept covered by mapping it to the old one. Analog...
Fertilization experiments using zona-free hamster eggs and spermatozoa from both guinea pig and human were conducted in the presence of cytochalasin D to evaluate the possible role of actin filaments in fertilization processes. When the actin filament inhibitor, cytochalasin D, was added to fertilization media at concentrations of 10 to 30 microM, penetration of eggs was significantly inhibited. Preincubation of the eggs with cytochalasin D and washing prior to addition of spermatozoa had no effect on penetration as quantitated by the number of swollen heads in the egg cytoplasm. However, spermatozoa preincubated with cytochalasin D and subsequently washed prior to egg addition showed reduced penetration of the same magnitude as when spermatozoa and eggs were coincubated with cytochalasin D. Both the percentage of zona-free eggs showing decondensed sperm heads and the penetration indices (total decondensed spermatozoa/total eggs) were significantly affected when spermatozoa were exposed to cytochalasin D. The DMSO vehicle used to dissolve cytochalasin D had little effect on the number of decondensed heads. When the concentration of cytochalasin D was increased (DMSO remaining constant) in human sperm experiments, percent penetration decreased and progressively fewer decondensed spermatozoa were recorded, indicating dose-responsiveness to cytochalasin D. Motility parameters of human spermatozoa were not altered at any of the concentrations of cytochalasin D tested. Neither guinea pig sperm motility nor acrosome reaction was altered significantly by cytochalasin D or the DMSO vehicle. These experiments suggest that cytochalasin D may be an inhibitor of some fertilization processes such as sperm penetration or sperm head decondensation.
Insights from the cognitive sciences indicate a continuing need for physicians to understand conceptual knowledge from the basic sciences, despite recent concerns regarding the increasing amount of information in medicine and the growing emphasis on performance skills. A 1987 survey of selected basic science and clinical teachers in North American medical schools was undertaken to identify basic biomedical concepts that are important in the practice of medicine and to specify how difficult these are for students to learn, apply, or both. Responses from faculty (nominated by their deans to answer the survey) from 82% of the medical schools indicated considerable agreement between the basic science teachers and clinical teachers on the relative importance of a set of biomedical concepts, and showed relatively minor levels of disagreement on how difficult these concepts are. The judgments of these teachers could prove extremely useful in (1) determining concepts that--because of their importance--should receive special attention in curriculum efforts, and (2) determining concepts that--because of their difficulty--need "special handling."
Evaluation of dynamic changes in pH and concentrations of adenosine 5'-triphosphate (ATP), phosphocreatine (PCr), and inorganic phosphate (Pi) during the transition from rest to steady-state exercise in the human has been methodologically limited. Previous work has relied on muscle biopsy of exercising subjects at different times in different exercise bouts. Chemical evaluation of metabolites has been hampered by continuing change in metabolic concentration during the biopsy procedure. Recently, Fourier-transformed 31P nuclear magnetic resonance (31P-NMR), employing surface coils, has made evaluation of phosphorus metabolites possible by noninvasive atraumatic means in human muscle. Relative concentrations of PCr, Pi, and ATP, together with pH, have been obtained with 31P-NMR from the flexor digitorum superficialis muscle on two occasions in four adult men during the transition from rest to exercise. [PCr] rapidly fell and was mirrored by a rise in [Pi]. The former temporarily exceeded the latter with the discrepancy apparently being absorbed by a transient rise in [ATP], which was itself mirrored by alteration in [H+].
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