When people first learn to categorize novel objects, they may use logical rules. These rules may be explicitly provided to them (e.g., Allen & Brooks, 1991; Palmeri, 1997; Palmeri & Nosofsky, 1995) or they might be induced from examples (e.g., Johansen & Palmeri, 2002; Nosofsky, Palmeri, & McKinley, 1994; Palmeri & Nosofsky, 1995). Indeed, in many categorization experiment, subjects report engaging in hypothesis testing when they learn categories, especially in the early stages of category learning. To account for this rule-based categorization behavior, we developed and tested a rule-plus-exception model of category learning called RULEX (Nosofsky, Palmeri, & McKinley, 1994; Nosofsky & Palmeri, 1998; Palmeri & Nosofsky, 1995). According to the model, people initially learn categories by forming simple rules and possibly memorize exceptions to those rules. A key aspect of the model is that different subjects form different rules and memorize different exceptions to those rules. Although average subject data could not discriminate between rule-based and exemplar-based categorization, examination of individual-subject response generalizations were far more consistent with rule-based than exemplar-based categorization.

Johansen, M.K., & Palmeri, T.J. (2002). Are there representational shifts during category learning? Cognitive Psychology, 45, 482-553.

Nosofsky, R.M., & Palmeri, T.J. (1998). A rule-plus-exception model for classifying objects in continuous-dimension spaces. Psychonomic Bulletin & Review, 5, 345-369.

Palmeri, T.J. (1997). Exemplar similarity and the development of automaticity. Journal of Experimental Psychology: Learning, Memory, and Cognition, 23, 324-354.

Palmeri, T.J., & Nosofsky, R.M. (1995). Recognition memory for exceptions to the category rule. Journal of Experiment Psychology: Learning, Memory, and Cognition, 21, 548-568.

Nosofsky, R.M., Palmeri, T.J., & McKinley, S.C. (1994). Rule-plus-exception model of classification learning. Psychological Review, 101, 53-79.

Nosofsky, R.M., Gluck, M., Palmeri, T.J., McKinley, S.C., & Glauthier, P. (1994). Comparing models of rule-based classification learning: A replication and extension of Shepard, Hovland, and Jenkins (1961). Memory & Cognition, 22, 352-369.