Teaching categories via examples and explanations.

People often learn categories through interaction with knowledgeable others who may use verbal explanations, visual exemplars, or both, to share their knowledge. Verbal and nonverbal means of pedagogical communication are commonly used in conjunction, but their respective roles are not fully understood. In this work, we studied how well these modes of communication work with different category structures. We conducted two experiments to investigate the effect of perceptual confusability and stimulus dimensionality on the effectiveness of verbal, exemplar-based, and mixed communication. One group of participants - teachers - learned a categorization rule and prepared learning materials for the students. Students studied the materials prepared for them and then demonstrated their knowledge on test stimuli. All communication modes were generally successful, but not equivalent, with mixed communication consistently showing best results. When teachers were free to generate as many visual exemplars or words as they wish, verbal and exemplar-based communication showed similar performance, although the verbal channel was slightly less reliable in situations requiring high perceptual precision. At the same time, verbal communication was better suited to handling high-dimensional stimuli when communication volume was restricted. We believe that our work serves as an important step towards studying language as a means for pedagogical category leaning.