Discourse-linking in agrammatic and fluent aphasia
Agrammatic speakers have problems with grammatical encoding and decoding. However, not all syntactic processes are equally problematic: present-time-reference/who-questions/reflexives can be processed by narrow syntax alone and are relatively spared compared to past-time-reference /personal pronouns/which-questions that need additional access to discourse and information structures to link to their referent outside the clause (Avrutin, 2006). Linguistic processing that requires discourse linking is difficult for agrammatic individuals: reference to the past is more difficult than to the present (Bastiaanse et al., 2011). The same holds for which-questions compared to who-questions and for pronouns compared to reflexives (Avrutin, 2006). These results were found in different populations in different languages. In the current study for the first time we tested all conditions within the same population. The research questions were:
- Are agrammatic and fluent aphasic speakers impaired in discourse-linked processes?
- Are discourse-linked processes similarly impaired in the domains of time reference, Wh-questions and pronouns/reflexives?
The results show that processing discourse-linking is not only affected in agrammatic but also in fluent aphasia. The effect was even larger in this fluent aphasic population and only in this group it is was visible in all three conditions. Such similar performance in agrammatic and fluent aphasia are in line with Bastiaanse & Edwards (2004) and are interpreted by assuming that complex linguistic operations are more difficult when language is impaired due to brain damage. We do not assume that the underlying deficit in both populations is similar, but we think that different underlying deficits affect similar grammatical operations. We assume that in agrammatic aphasia grammatical decoding is impaired, whereas in fluent aphasia lexical access is compromised. For optimal sentence comprehension, both processes should be impeccable, otherwise complex syntactic operations, for example the ones that require discourse processing, are not comprehended correctly.