Linguistic complexity and frequency in agrammatic speech production.

There is a long standing debate between aphasiologists on the essential factor that constitutes the behavioral patterns of loss and preservation in agrammatic Broca's aphasia. It has been suggested that linguistic complexity plays a crucial role: linguistically complex structures are more difficult to produce than linguistically simple ones. However, linguistic complex structures are often less frequent in a language; for example, simple active sentences are more frequently used than linguistically more complex passive sentences. Hence, it might be that it is not linguistic complexity but frequency that determines agrammatic behavior. Frequency may play a role at several levels. For agrammatic patients, for example, the frequency of sentence constructions may be crucial, whereas for fluent aphasic speakers word frequency influences performance. The present study presents corpus frequency data for constructions that have previously been used to show the influence of linguistic complexity on Dutch agrammatic speech production. These are data on: (1) verb movement; (2) object scrambling; and (3) verbs with alternating transitivity. We compared the data of our corpus research with the performance of agrammatic speakers on the constructions. The conclusion is that frequency cannot account for the data, but linguistic complexity can. It is then discussed what 'linguistic complexity' exactly stands for, in terms of the word order deficit in agrammatic aphasia.