On the Category Adjustment Model: Another look at Huttenlocher, Hedges, and Vevea (2000)

Huttenlocher, Hedges, and Vevea (2000) (Why do categories affect stimulus judgment? Journal of Experimental Psychology: General, 129, 220-241) introduce the category adjustment model (CAM), which posits that participants imperfectly remember stimuli in serial judgment tasks. In order to maximize accuracy, CAM holds that participants use information about the distribution of the stimuli to improve their judgments. CAM predicts that judgments will be a weighted average of imperfect memories of the stimuli and the mean of the distribution of stimuli. Huttenlocher, Hedges, and Vevea (2000) report on three experiments and the authors conclude that CAM is “verified.” We attempt to replicate Experiment 3 from Huttenlocher et al. (2000). We analyze judgment-level data rather than averaged data. We find evidence of a bias toward a set of recent stimuli rather than a bias toward the running mean. We also do not find evidence of the joint hypothesis that the participants learned the distribution of stimuli and employed this information in their judgments. The judgments in our dataset are not consistent with CAM. We discuss how the apparent defects in HHV went unnoticed and how such mistakes can be avoided in future research. Finally, we hope that the techniques that we employ will be used to test other datasets that are currently regarded as consistent with CAM or any Bayesian model of judgment.