2. Models Presented

ABSTRACT This chapter introduces the two theoretical models to be applied to qualitative and quantitative data in the case study of Dodge Morgan. We present the five-factor model (FFM) and the life-story model (LSM) separately, with attention to their differing origins, assumptions, and utilities. We briefly trace the development and resurgence of the factor-analytic FFM and delineate the extent of its current influence in the field of personality. We discuss individual factors and consider the ways in which the model can be expected to be useful as well as limited in application to the individual. We next present the genealogy of the narrative, constructivist LSM and describe its components; we also discuss its contrasting strengths and limitations.     

6. The Life Voyage

ABSTRACT Chapter 6 applies the five-factor model and the life-story model as complementary perspectives to the multiple data sources collected for the case study of Dodge Morgan. We integrate the two models to create a new level of analysis that captures differing aspects of experience. We develop a holistic personality analysis of Morgan, interpreting his childhood, young manhood, adventures in Alaska and on the boat Coaster, his return to the mainland and embrace of business and entrepreneurship, and his solo circumnavigation. We address questions of voyage outcomes with reference to the quantitative analyses of his voyage log; we consider not only the external journey but also his internal psychological issues and developmental tasks.     

Comparing Locomotion With Lever-press Travel In An Operant Simulation Of Foraging

An operant model of foraging was studied. Rats searched for food by pressing on the left lever, the patch, which provided one, two, or eight reinforcers before extinction (i.e., zero reinforcers). Obtaining each reinforcer lowered the probability of receiving another reinforcer, simulating patch depletion. Rats traveled to another patch by pressing the right lever, which restored reinforcer availability to the left lever. Travel requirement changed by varying the probability of reset for presses on the right lever; in one condition, additional locomotion was required. That is, rats ran 260 cm from the left to the right lever, made one response on the right lever, and ran back to a fresh patch on the left lever. Another condition added three hurdles to the 260-cm path. The lever-pressing and simple locomotion conditions generated equivalent travel times. Adding the hurdles produced longer times in patches than did the lever-pressing and simple locomotion requirements. The results contradict some models of optimal foraging but are in keeping with McNair's (1982) optimal giving-up time model and add to the growing body of evidence that different environments may produce different foraging strategies.     

Stochastic ordering using the latent trait and the sum score in polytomous IRT models

In a restricted class of item response theory (IRT) models for polytomous items the unweighted total score has monotone likelihood ratio (MLR) in the latent trait. MLR implies two stochastic ordering (SO) properties, denoted SOM and SOL, which are both weaker than MLR, but very useful for measurement with IRT models. Therefore, these SO properties are investigated for a broader class of IRT models for which the MLR property does not hold.In this study, first a taxonomy is given for nonparametric and parametric models for polytomous items based on the hierarchical relationship between the models. Next, it is investigated which models have the MLR property and which have the SO properties. It is shown that all models in the taxonomy possess the SOM property. However, counterexamples illustrate that many models do not, in general, possess the even more useful SOL property.Hemker's research was supported by the Netherlands Research Council, Grant 575-67-034. Junker's research was supported in part by the National Institutes of Health, Grant CA54852, and by the National Science Foundation, Grant DMS-94.04438.     

Neural Network Models and Mechanisms of Strategy Development

The focus of this paper is mechanisms that may be responsible for intellectual and developmental differences in the cognitive strategies of typical and atypical children, including those with mental retardation. The discussion of these mechanisms is based on behavioral experiments on external memory strategies and on a set of neural network models designed for these tasks. Following the review of the external memory research, the rationale for using neural network models, how they have been used in other research, and their specific application to intellectual and developmental differences in external memory, including the results of several simulations, are reviewed. This is followed by a discussion of the mechanisms of intellectual differences and developmental change included in the models and some challenges for this type of modeling. Neural network modeling is discussed as an asset to research on cognitive development.