Diss. (sammanfattning) Umeå : Umeå universitet, 2007. / Härtill 4 uppsatser.

Judgments that demand consideration of pieces of information in the environment occur repeatedly throughout our lives. One professional example is that of a physician that considers multiple symptoms to make a judgment about a patient’s disease. The scientific study of such, so called, multiple-cue judgments that involve multiple pieces of information (cues: e.g., symptoms) and continuous criterion (e.g., blood pressure) has been concerned with the statistical modelling of judgment data (see Brehmer, 1994; Cooksey, 1996; Hammond & Stewart, 2001). In this thesis behavioural experiments, cognitive modelling and brain imaging is used to investigate an adaptive division of labor between multiple memory representations in multiple-cue judgment. It is hypothesized that the additive, independent linear effect of each cue can be explicitly abstracted and integrated by a serial, additive judgment process (Einhorn, Kleinmuntz, & Kleinmuntz, 1979). It is further hypothesized that a variety of sophisticated task properties, like non-additive cue combination, nonlinear relations, and inter-cue correlation, are carried implicitly by exemplar-memory (Medin & Schaffer, 1978; Nosofsky, 1984; Nosofsky & Johansen, 2000). Study I and II investigates the effect of additive versus non-additive cue-combination and verify the predicted shift in cognitive representations as a function of the underlying cue-combination rule. The third study is a review that discusses the nature of these representational shifts; are they contingent upon early perceived learning performance instead of automatic and error-driven? Study IV verifies that this shift is evident also in the neural activity associated with making judgments in additive and non-additive tasks.

This thesis investigates the cognitive processes and representations underlying human judgment in a multiple-cue judgment task. Several recent models as-sume that people have several qualitatively distinct and competing levels of knowledge representations (Ashby, Alfonso-Reese, Turken, & Waldron, 1998; Erickson & Kruschke, 1998; Nosofsky, Palmeri, & McKinley, 1994; Sloman, 1996). The most successful cognitive models in categorization and multiple-cue judgment are, respectively, exemplar-based models and cue abstraction models. The models are different in the computations and processes implied, but the structure of the task is similar. Study 1 investigated if the different theoretical conclusions in categorization and multiple-cue judgment derive from genuine differences in the processes, or are accidental to the different research methods. In Study 2, we expected learning in dyads to promote explicit cue abstraction as a consequence of verbalization (a social abstraction effect) and performance to improve due to the larger joint exemplar knowledge base (an exemplar pooling effect). In Study 3 we used the generalized model Sigma to illustrate how change in task environments (linear vs. nonlinear) can shape the knowledge representation that is used. We expected that people are not able to use cue ab-straction when judging objects with a non-linear structure between the visual cues (features) of the objects and the criterion, and therefore they are forced to use exemplar-based processes. Taken together, the results of these studies indicate that differences that characterize typical categorization and multiple-cue judgment tasks are conducive of qualitatively different cognitive processes, and that the task environment plays an important role for which cognitive processes are used in multiple cue judgments.