Label Similarity and Stimulus Similarity Interact in Categorization

When learning to categorize stimuli, do we assume similar things should have similar labels? Are people more likely to respond with closer labels (e.g. 2-1 vs 2-4) when stimuli are more similar to each other? Across five experiments, we report evidence of such a bias and demonstrate that it can surface across a wide range of stimulus modalities and features, and persists regardless of participants' prior knowledge of the dimensions relevant for categorization. We also characterize some of the limits of this effect: it appears sensitive to the specific configuration of label-stimulus mappings, and may depend on overt similarity relations in label space. At minimum, our findings indicate the need to consider label-stimulus configurations when designing categorization experiments. They also hint more broadly at how label-to-stimulus mappings may affect how we structure novel categories.