Proceedings of the Annual Meeting of the Cognitive Science Society

How do people decide whether or not an item belongs to a new category, the variability o-f which they do not know We postulate that people have a de-fault similarity distance (DSD) which they use when no other in-formation about the variability o-f a category is available. To test our claim, subjects were asked to tell how they would instruct a being from another world to distinguish members o-f a category, by shoMnng pictures. The categories were from different levels thus dif-fering in variability. For highly variable categories subjects tended to present multiple positive instances (thus indicating their extraordinary variability), whereas -for narrow categories they tended to present negative instances (thus explicitly delimiting them). These results indicated that a norm, relative to which additional in-formation is supplied, lay in between. Indeed, there was a level at which subjects apparently relied on DSD, -finding it sufficient to show but a single exemplar of the categor/. This happened with basic-level categories -for 3th graders and adults and with subordinate categories -for 2nd graders, thus demonstrating a developmental trend in what is considered a normal standard category.