Academic journal article Memory & Cognition

Knowledge Partitioning in Categorization: Boundary Conditions

Academic journal article Memory & Cognition

Knowledge Partitioning in Categorization: Boundary Conditions

Article excerpt

Knowledge partitioning refers to the notion that knowledge can be held in independent and non-overlapping parcels. Partitioned knowledge may cause people to make contradictory decisions for identical problems in different circumstances. We report two experiments that explored the boundary conditions of knowledge partitioning in categorization. The studies examined whether or not people would partition their knowledge (1) when categorization rules were or were not verbalizable and (2) when the to-be-categorized stimuli comprised perceptually separable or integral dimensions. When learning difficulty was controlled, partitioning occurred across all combinations of verbalizability and integrality/separability, underscoring the generality of knowledge partitioning. Partitioning was absent only when the task was rapidly learned and people reached a high level of proficiency, suggesting that task difficulty plays a critical role in the emergence of partitioned knowledge.

The knowledge partitioning framework is based on the idea that knowledge, rather than being represented as an integrated whole, may be fractionated into independent parcels that are used selectively without reference to knowledge held in other parcels (see, e.g., Lewandowsky, Kalish, & Ngang, 2002; Lewandowsky & Kirsner, 2000; Yang & Lewandowsky, 2003). As a consequence, people may provide contradictory answers to an identical problem, depending on which knowledge parcel they use to guide their answer.

Knowledge partitioning has been demonstrated with experts (Lewandowsky & Kirsner, 2000), with nonexpert participants in a function learning paradigm (Lewandowsky et al., 2002), and with nonexpert participants in categorization tasks involving numeric (Yang & Lewandowsky, 2003) and perceptual stimuli (Yang & Lewandowsky, 2004). In each instance, a normatively irrelevant context cue (such as a verbal label or stimulus color) served as the basis for the contradictory resolution of an identical problem. This contradiction, elicited by the mere switch of the context cue without alteration of the surface structure of the problem, distinguishes partitioning from other well-known context effects (see Kalish, Lewandowsky, & Kruschke, 2004).

To illustrate, consider the study by Lewandowsky and Kirsner (2000) in which expert firefighters had to predict the spread of simulated wildfires. Firefighters were provided with the physical predictors of fire spread in two different contexts: back-burn or to-be-controlled. (A back-burn is a fire lit by fire fighters in the path of an advancing to-be-controlled fire to starve it of fuel.) In reality, any fire will preferentially spread with the wind and up slopes. It follows that if the two variables are placed in opposition, the direction of a fire is not immediately obvious: With light downhill winds, slope may be the overriding variable, and the fire may spread uphill. Conversely, if the opposing wind is sufficiently strong, a fire may spread with the wind and hence downhill. Whether the fire is a back-burn or to-be-controlled is physically irrelevant; however, Lewandowsky and Kirsner found that experts expected an identical fire to spread uphill against the wind if presented as a back-burn, and downhill with the wind if presented as a to-be-controlled fire. In contrast to the widely accepted view that expertise is highly integrated (e.g., Bédard & Chi, 1992; Glaser, 1996; see Lewandowsky et al., 2002, for a review of the integration assumption), this finding suggests that experts possess independent parcels of knowledge that are selectively accessed on the basis of context and without regard to knowledge in other parcels. Although the apparent partitioning of knowledge necessarily causes errors in certain situations, the firefighters' context-bound behavior is nonetheless statistically appropriate: Because back-burns are lit only when winds are light, slope tends to be particularly relevant. …

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