So many options, so little time: the roles of association and competition in underdetermined responding.

How do we make decisions when faced with multiple options? In the domain of language, some evidence suggests that we exert cognitive control in order to respond in such underdetermined situations when a good option is hard to find but not when we must select among competing options. However, this conclusion, and conclusions about the neural substrates supporting underdetermined responding, are made on the basis of measures that confound retrieval and selection demands. The present study introduces measures based on latent semantic analyses that better capture the underlying theoretical constructs of association strength and competition. These measures revealed independent effects of retrieval and selection demands on reaction times in verb generation and sentence completion tasks. These results challenge existing accounts of underdetermined responding and highlight the need for unconfounded measures of association strength and competition in studies of localization. We propose a new model governed by both absolute and relative activation levels of alternative responses.