Subject-verb agreement constitutes a robust characteristic of French. However, especially at beginner and intermediate levels, second language (L2) learners might substitute or fail to recognize an infinitive for a conjugated verb, or a 3rd person singular form for a plural form, as "Les enfants mangera" (The children will eat--3rd person singular) for the expected "Les enfants mangeront" (The children will eat--3rd person plural). The opposite error type, where an L2 learner would produce a plural verb form when a singular one is expected very rarely occurs. According to underspecification theory, a singular form is underspecified for number: a number value is not specified. It may sometimes be incorrectly inserted in a context requiring a specified plural value because the underspecified form partially satisfies the requirements of the context. In contrast, with a form that has an incorrect value specification in context, there is no grammatical source for that value. I argue that in order to determine that an underspecified form has been incorrectly produced, one needs to perform a real-time inference Ø[right arrow][-value] and maintain the inferred value in the focus of attention. I argue that this inference is reliant on a Central Representational System that supports the operations of various modules. Interactions between grammatical processing and other areas of cognition, such as vision and the conceptual system, are predicted. L2 learners and native speakers of French were tested on listening and reading tasks with picture classifications during grammatical processing. The type of error was manipulated. Results show picture classification times modulated by error type. The longest classification times were produced when respondents read or listened to an underspecified form when a specified verb form was expected, presumably because performing the real-time inference O[right arrow][-Plural] took away resources from visual/conceptual processing. This argues that general processes aid in the computation of grammatical representations. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]