Modeling item responses when different subjects employ different solution strategies

A model is presented for item responses when different subjects employ different strategies, but only responses, not choice of strategy, can be observed. Using substantive theory to differentiate the likelihoods of response vectors under a fixed set of strategies, we model response probabilities in terms of item parameters for each strategy, proportions of subjects employing each strategy, and distributions of subject proficiency within strategies. The probabilities that an individual subject employed the various strategies can then be obtained, along with a conditional estimate of proficiency under each. A conceptual example discusses response strategies for spatial rotation tasks, and a numerican example resolves a population of subjects into subpopulations of valid responders and random guessers.The first author's work was supported by Contract No. N00014-85-K-0683, project designation NR 150-539, from the Cognitive Science Program, Cognitive and Neural Sciences Division, Office of Naval Research. We are grateful to Murray Aitkin, Isaac Bejar, Neil Dorans, Frederiksen, and Marklyn Wingersky for their comments and suggestions, and to Alison Gooding, Maxine Kingston, Donna Lembeck, Joling Liang, and Kentaro Yamamoto for their assistance with Example 2.     

A measure of semantic complexity among predications

A scale for assessing the complexity or density of utterances was developed using 10 categories ofsemantic relations (e.g., temporal ordering, causality). The categories are inferable from the particular meanings of the words (e.g., connectives, particular tense variations) used in an utterance. The scale was applied to three samples of subjects to assess its interjudge reliability and to compare the utterances of fourth-, sixth-, and eighth-grade children from middle- and working-class neighborhoods. It was also used to compare the complexity of utterances for different types of visual stimuli (used to elicit language samples). Interjudge reliabilities were more than acceptable for each of the samples, and significant differences in semantic density were found across grade, between children from working-class and middle-class neighborhoods, and for the stimuli used to elicit the utterances. When two of the three types of eliciting visual stimuli were equated for content and exposure conditions, the differences in verbal density between eliciting conditions were not replicated. The usefulness of the scale for assessing utterance density and by implication, comprehension difficulty of utterances and of texts, is discussed.This study was supported in part by a Grant from the National Institute of Education, U.S. Department of Health, Education and Welfare, Complexity in Auditory and Graphics Communication, Project No. 4-470. Points of view or opinions stated here do not necessarily represent National Institute of Education position or policy.     

Metaphysics of causation

Conclusion The world contains not only causes and effects, but also causal relations holding between causes and effects. Because causal relations enter into the structure of the world, their presence has various modal and probabilistic consequences. Causation and necessary and sufficient conditions do often go hand in hand. Causation, however, is a robust ingredient within the world itself, whereas modalities and probabilities supervene on the nature of the world as a whole, and on the resulting relations between one possible world and others. Some modalities, therefore, are essentially causal; but causation is not essentially modal.¹⁹     

Proof and truth in Lakatos's masterpiece

Proofs and Refutations is Lakatos's masterpiece. This article investigates some of its central themes, in particular: the nature of proofs ('Proofs do not prove, they improve'); the nature of definitions (real, not nominal); and the consequences of all this for ontology (platonism vs Popper's World Three).     

Inquiry into intentional systems I: Issues in ecological physics

Summary The role of intention in guiding the behavior of goal-directed systems is a problem that continues to challenge behavioral science. While it is generally agreed that intentional systems must be consistent with the laws of physics, there are many obvious differences between inanimate, physical systems and sentient, intentional systems. This suggests that there must be constraints over and above those of physics that govern goal-directed behavior. In this paper it is suggested that generic properties of self-organizing mechanisms may play a central role in the origin and evolution of intentional constraints. The properties of self-organizing systems are first introduced in the context of simple physical systems and then extended to a complex (biological) system. Whereas behavior of an inanimate physical system is lawfully determined by force fields, behavior of an animate biological system is lawfully specified by information fields. Biological systems are distinguished from simple physical systems in terms of their ubiquitous use of information fields as special (biological and psychological, social, etc.) boundary conditions on classical laws. Unlike classical constraints (boundary conditions), informational constraints can vary with time and state of the system. Because of the nonstationarity of the boundary conditions, the dynamic of the system can follow a complex trajectory that is organized by a set of spatially and temporally distributed equilibrium points or regions. It is suggested that this equilibrium set and the laws that govern its transformation define a minimal requirement for an intentional system. One of the benefits of such an approach is that it suggests a realist account for the origin of semantic predicates, thereby providing a basis for the development of a theory of symbolic dynamics. Therefore, the principles of self-organization provide a comprehensive basis for investigating intentional systems by suggesting how it is that intentions arise, and by providing a lawful basis for intentional behavior that reveals how organisms become and remain lawfully informed in the pursuit of their goals.     

False recognition of associates: How robust is the effect?

False recognition of nonpresented words that were strong associates of 12 words in a study list was examined. Six lists were read to subjects; each list contained the 12 strongest associates to a critical nonpresented word. False-alarm rates to the 6 critical nonpresented words were obtained under several different conditions. The manipulations included varying the level of processing done to the study lists, varying the recognition-test procedure, repeating each of the study lists three times, and mixing the words from the six study lists together. A reliable false-recognition effect for critical nonpresented words was obtained in all conditions. However, the effect was not impervious to all of the manipulations. Significantly lower false recognition was obtained when learning was incidental as well as when the words on the six lists were mixed together. Neither level of processing nor repetition significantly influenced false recognition. This last result is inconsistent with Hintzman’s (1988) MINERVA 2 global memory model, but agrees with predictions from Shiffrin, Ratcliff, and Clark’s (1990) SAM model.     

The Future of Psychology in Medicaid's Health Delivery System for People with Disabilities

State Medicaid programs are rapidly converting fee-for-service health delivery systems to managed care for people with disabilities. In theory, managed care models of health delivery will substantially improve the quality of care for people with disabilities, but in reality, few successful models exist. This period of transition holds both opportunities and challenges for psychologists in medical settings. Because Medicaid reforms for people with disabilities may herald similar reforms for both the public and the private sectors, psychology's response will determine its role in the future of health care delivery for this population. Changes in training and increased attention to outcomes research, innovations in practice, and advocacy will be the keys to success.