Parts in object concepts: experiments with artificial categories.

Previous research has demonstrated that basic-level categories are associated with the parts of objects. Five experiments were conducted to investigate whether this correlation is caused by a psychological principle that requires basic concepts to have common parts. This hypothesis was investigated in the experiments by separating part and nonpart information in artificial categories. Basic-level structure was measured in two ways: as the level with the highest ratio of within-category similarity to between-category similarity, and as the level with the fastest categorization time in an object-identification task. The results revealed that basic-level structure could be found in categories that did not have parts in common. Furthermore, nonpart information, such as size, color, and texture, could both enhance the basic level and eliminate the basic-level advantage, depending on whether the nonpart information was consistent with or contradicted the part information. These results suggest that, psychologically, parts are neither necessary nor sufficient to form a basic level.