Submitted to the International Conference “The Science of Aphasia V,” Potsdam, Germany, 16-21 September 2004.

Background and research questions

Verbal inflectional errors are among the most prominent characteristics of aphasic non-fluent speech (e.g., Goodglass, 1976). However, a number of studies have shown that such impairment is selective and that not all verbal inflectional morphemes are equally disturbed. Subject-verb agreement is relatively intact (e.g. De Bleser & Luzzatti, 1994) while tense is severely impaired (e.g. Friedmann & Grodzinsky, 1997). Two types of accounts have been proposed to explain these findings. Some researchers view the deficit that non-fluent individuals exhibit as structural and thus attribute verbal inflectional errors to a breakdown of functional categories and their projections. Specifically, Friedmann & Grodzinsky (1997) and Grodzinsky (2001) have argued that impairment in agrammatic production can be characterised in terms of a deficit in the syntactic tree. Agrammatic individuals produce trees that are intact up to the Tense node and ‘pruned’ from this node up. Other researchers have suggested that difficulties in the production of particular inflectional morphemes are due to processing limitations (e.g., Crain, Ni, & Shankweiler, 2001). Within such accounts, grammatical representations are intact but access to them is impaired. The asymmetry in the performance of aphasic individuals on production vs. grammaticality judgement tasks has been taken as further evidence for such approaches (Linebarger, Schwartz, & Saffran, 1983).

The purpose of the present study was to investigate functional categories in Greek aphasia across different tasks. Specifically, in order to contrast structural and processing theoretical approaches to morphological impairments in aphasia, we investigated (a) the relative sensitivity of functional categories to brain damage and the systematicity thereof; and (b) the relation between production and comprehension performance.

Greek language

(Modern) Greek is a null-subject language with rich morphology and relatively free word order. The Greek verbal paradigm distinguishes six person inflections, and also makes an aspectual distinction between perfective and imperfective aspect, which surfaces in the verb stem. The aspectual distinction shows up in the past tense and in the future. There is no aspectual distinction in the present tense, which always uses the imperfective stem.

Given the richness of the Greek inflectional paradigm, several functional categories are instantiated in the extended projection of the Greek verb (Philippaki-Warburton, 1987). The order of these categories though remains quite controversial. According to Philippaki-Warburton (1998) and Alexiadou & Anagnostopoulou (1996), AgrP is higher than TP (but not according to Tsimpli, 1990). Therefore, the likely clause structure for Greek is:

(1)      CP > MoodP > NegP > AgrP > TP > VoiceP > AspectP > VP

Method

Eight individuals (1 female) aged 42–81 years, clinically diagnosed with aphasia, were referred by speech-language pathologists to participate in the study. All had suffered a left-hemisphere cerebrovascular accident 3 or more months before testing. Their fluency was assessed using a simple speech rate measurement, there being no standardised testing materials in the Greek language. Each participant was tested for comprehension, using a grammaticality judgment task, and for production, using a sentence completion task and a picture description task (cookie theft and a store situation). Grammaticality judgment and sentence completion used the same set of sentences, in different sessions, to ensure comparability of comprehension and production measurements. The sentences were constructed to assess three functional categories: (a) subject-verb agreement (32 items); (b) tense (16 items); and (c) aspect (32 items). The number of trials for the grammaticality judgment was double that for production in order to include an equal number of incorrect sentences. Eight verbs were used to construct the sentences, balancing frequency of use (estimated on the basis of subjective familiarity measured on an independent sample) and regularity of aspectual conjugation.

Results

The table shows the proportion of incorrect responses for each participant, separately for each task and functional category. The most striking observation is the range of ability exhibited by this participant group, from flawless performance (Participant 5, especially production) to total inability to perform the task (Participant 6, no production at all). However, in this diverse group, several systematic patterns emerge upon closer inspection.

Discussion

Performance on subject-verb agreement tends to be least impaired, accounting for up to 23% of an individual’s total errors in comprehension and up to 49% in production. Tense and aspect are more impaired, with errors in aspect ranging from 33% to 85% of an individual’s comprehension errors and from 34% to 61% in production. Tense errors are particularly interesting, in that they make up only a small proportion of the total individual errors of the least impaired participants (1, 7, and 8) but a large proportion of the total individual errors, even more than aspect errors, for the most impaired participants (2, 3, and 4).

Given the clause structure of Greek shown in (1), a structural account such as the tree pruning hypothesis would predict that aspect would be least impaired while subject-verb agreement would be more (if not most) impaired, a pattern opposite from the one observed. Therefore, our findings do not support this hypothesis. Taking into account that we found a higher proportion of production than comprehension errors in almost every case, our results would seem to be most compatible with some processing accounts.

Our findings are consistent with the conclusions of Stavrakaki & Kouvava (2003), who found that “high or low tree position in the sentence hierarchy was not the only determinant of the aphasic performance,” and attributed the aphasics’ difficulties to impaired access rather than impaired grammatical representations. Similarly, Tsapkini, Jarema, & Kehayia (2001) proposed a computational load deficit to account for their observations regarding inflectional impairments in the Greek verb on repetition, reading, and elicitation tasks.