A Theory of Grammatical Impairment in Aphasia

In this paper we will present an overview of a new theory of grammatical impairment in aphasia called adaptation theory. We begin by introducing a basic distinction between two kinds of deviant behavior: negative symptoms, which result when the patient tries to behave the same way as he did premorbidly, and positive symptoms, which are the consequence of a process of adaptation by which behavioral goals are changed. This analysis is then applied to grammatical impairment in aphasia and to the traditional distinction between agrammatism and paragrammatism. It is argued that whereas paragrammatic speakers are the ones who keep trying to produce fully elaborated sentences as they used to before their illness, agrammatics make a strategic choice in favor of abbreviated forms, which leads to telegraphic speech. It is maintained that for this purpose they employ the normal capacity to produce elliptical sentences. We discuss the most direct evidence for this latter claim: that telegraphic speech as produced by agrammatic speakers is grammatical, if analyzed as a sequence of elliptical strings. A second prediction derives from the assumption that the shift to telegraphic speech is due to a strategic choice rather than being a mandatory way of speaking, given the impairment. Evidence is presented suggesting that this choice can be affected by pay-off manipulations, which result in a completely different behavior: Paragrammatic rather than agrammatic output is observed.