Two experiments in category learning are used to examine two types of categorization models. In both a two and four choice experiment, subjects are shown to fail to learn to optimally classify two dimensional stimuli. The general recognition theory (CRT) of Ashby & Maddox (1990) predicts quadratic decision bounds. The first experiment disconfirms this. The extended GR T predicts that learners adopt a bound of complexity equivalent to the optimal one. The second experiment disconfirms this as well. Both experiments support the idea that general resources of adaptive systems can provide explanations of observed sub-optimal behavior.

We study the performance of human subjects in a task which requires multi-jointed reaches to be made to targets spaced over a wide area. In accordance with established research, we find that subjects' reaches are not accurate when they carmot see either their hands or the targets. The errors subjects make are different at different targets, suggesting that they are due to an error in the plaiming of movements. However, contrary to existing models of this error, we find that it is highly idiosyncratic. This leads to the rejection of the most straightforward model of how reaching is learned, and poses problems which a future model must address.

In categorization research, competing theories are typically compared by fitting their predictions to participant’s responses on a set of test items. The theory that best matches each participant's responses is identified as the strategy the participant is most likely employing. Researchers face considerable difficulty in selecting the best-fitting model due to several factors. In this study, we show the frailty of this approach. Due to pervasive model mimicry and across the similarity- and rule-based models, typical categorization task designs fail to reliably distinguish strategies. Some design modifications that might help are counter-indicated on practical grounds (e.g., carry-over effects); other possible means of improving strategy identification are also discussed.