Free Classification: Evidence for an Analytic System of Overall Similarity Sorting

It has been shown that when people are asked, in the absence of experimenter feedback, to free classify stimuli into categories that appear natural to them, they tend to sort on the basis of a single dimension (e.g. Medin et al., 1987) rather than by overall similarity. This result is somewhat surprising considering that many natural categories appear to be organized around a number of characteristic features rather than a single defining feature. Overall similarity (OS) sorting has often been considered to be due to a primitive, non-analytic process whilst unidimension (UD) sorting has been viewed as the result of a verbal, analytic process (e.g. Kemler Nelson, 1984). According to this theory, the experimental setting in which free classification is often studied encourages a more deliberate, analytic approach and hence single dimension sorting dominates. In contrast, when individuals are encouraged to classify non-analytically there is evidence that overall similarity sorting can be increased. More recently, however, it has been proposed that, at least under certain conditions, overall similarity sorting can be due to an effortful analytic, dimensional summation strategy (Milton and Wills, 2004). Three experiments are reported which further examine the contention that overall similarity sorting can be the result of an analytic process. All experiments employed a sequential match-to-standards procedure.