Examples from Chinese, Thai, and Finnish illustrate why researchers cannot always be confident about the precise nature of the word unit. Understanding ambiguities regarding where a word begins and ends, and how to model word recognition when many derivations of a word are possible, is essential for universal theories of reading applied to both developing and expert readers.

As the number of computational models of eye-movement control in reading increases, so too will their coverage and complexity. This will make their comparison and testing increasingly challenging. We argue here that there is a need to develop a methodology for constructing and evaluating such models, and outline aspects of a possible methodology.

In her Behavioral and Brain Sciences target article, Greenfield (1991) proposed that early in a child's development Broca's area may serve the dual function of coordinating object assembly and organizing the production of structured utterances. As development progresses, the upper and lower regions of Broca's area become increasingly specialized for motor coordination and speech, respectively. This commentary presents a connectionist simulation of aspects of this proposal. The results of the simulation confirm the main thrust of Greenfield's argument and suggest that an important impetus for the developmental differentiation in Broca's area may be the increasing complexity of the computational demands made upon it.