This will be a dry run of Cat’s AMLAP talk:

Communication leads to the emergence of sub-optimal category structures

Words divide the world into labelled categories. Languages vary in the categories they label, sometimes to the point of making cross-cutting divisions of the same domain (e.g. spatial relations: Choi, McDonough, Bowerman, & Mandler, 1999). A potential reason for this is that linguistic categories are constructed partly via communication. Previous work suggests two opposing hypotheses about how communication might contribute to category structure: 1) communication dynamically creates one of a number of optimally shareable category structures (Freyd, 1983; Gärdenfors, 2000); 2) the category structures resulting from communication are not necessarily optimal, but diverge from a shared similarity space in language-specific ways (Malt, Sloman, Gennari, Shi, & Wang, 1999). We had participants categorise images drawn from a continuous space in three conditions: a) a non-communicative condition, where participants viewed the whole set of images and divided it into categories on the basis of similarity; b) a second non-communicative condition, where participants created categories by categorising the set of images in an incremental, serial fashion; c) a communicative condition, where participants created categories in the same incremental, serial fashion as condition b), but in the course of playing a partnered communication game. Communicative participants produced systems with more categories than those of non-communicative participants. Communicators’ categories were also more variably sized, dividing the space up in less balanced ways than non-communicators in condition a), with non-communicators in condition b) intermediate between the two. These results suggest that communication creates a pressure for specificity, encouraging more and finer-grained categories. In addition, supporting the second hypothesis outlined above, the negotiation process and memory constraints involved in building up a communication system from scratch lead to category systems that diverge in sub-optimal ways from an underlying similarity space.

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