Agrammatic patterns in Alzheimer's disease: Evidence from tense, agreement, and aspect

Abstract

Background: Little research has been conducted on functional categories in probable Alzheimer's disease (pAD). Furthermore, the findings are contradictory, since some studies report ceiling performance on tense and/or subject–verb agreement (Kaprinis & Stavrakaki, 2007; Kavé & Levy, 2003), whereas others report morphosyntactic deficits and agrammatic profiles (e.g., Altmann, Kempler, & Andersen, 2001).

Aims: This study investigates the ability of Greek-speaking pAD individuals to produce and judge subject–verb agreement, tense, and aspect. Given pAD individuals have working memory limitations (e.g., Baddeley, 1996), and given the differential processing demands of agreement, tense and aspect (e.g., Fyndanis, Varlokosta, & Tsapkini, 2012a), pAD participants are expected to perform better on agreement than on tense/aspect. Based on the hypothesis that reference to the past is computationally more demanding than reference to the future/present (e.g., Bastiaanse et al., 2011), a within-tense dissociation is expected to emerge. Further, on the assumption that unmarked values of functional categories are less demanding than marked values (e.g., Lapointe, 1985), the imperfective (unmarked) aspect is expected to be better preserved than the perfective (marked) aspect.

Methods & Procedures: Ten Greek-speaking mild pAD individuals and six healthy controls participated in a sentence completion task, a grammaticality judgement task, and a sentence–picture matching task. Non-parametric tests were used for analysis of results.

Outcomes & Results: PAD participants were found to be significantly more impaired in aspect compared to tense and agreement, in both production and grammaticality judgement/comprehension. Agreement was found significantly better preserved than tense in production. Similar patterns of performance have been attested in agrammatism (e.g., Fyndanis et al., 2012a). Reference to the past and reference to the future did not dissociate, whereas the imperfective aspect was found to be significantly more impaired than the perfective aspect in production.

Conclusions: PAD participants' better performance on producing agreement, compared to tense/aspect, is accounted for in terms of the differential demands these categories pose on the processing system. Agreement is computationally less demanding than tense/aspect, because the former involves processing of grammatical information only, whereas the latter involve processing and integration of grammatical and extralinguistic/conceptual information. The preponderance of tense over aspect is attributed to the subjectivity of the latter, which renders it either a category “difficult” to test, or a computationally more demanding condition. The results also show that reference to the past is as demanding as reference to the future. The hypothesis that unmarked values are easier than marked ones is not supported by our data.

Keywords:

• Alzheimer's disease
• Tense
• Agreement
• Aspect
• Aphasia
• Greek

Acknowledgments

Many thanks go to the individuals who participated in this study. We are grateful to the audiences of the 49th Annual Meeting of the Academy of Aphasia (October 2011, Montreal, Canada), the 32nd Annual Meeting of the Department of Linguistics, School of Philosophy, Aristotle University of Thessaloniki (May 2011, Thessaloniki, Greece), and the 7th Panhellenic Conference on Alzheimer's Disease and Related Disorders (February 2011, Thessaloniki, Greece) for providing useful comments. We also express our gratitude to Sergey Avrutin, Spyridoula Varlokosta, Kyrana Tsapkini, Konstantinos Frangakis, Theodora Trachanopoulou, Ekaterini Klepousniotou, Maria Kambanaros, Dionysios Tafiadis, and Stavroula Stavrakaki for discussing with us issues related to this work, as well as to two anonymous reviewers for their useful comments and suggestions.

Notes

¹ These three tasks were administered 15 months after the initial MMSE (see Table 2) and the first two experimental tasks had been administered. Eight pAD participants and five healthy individuals participated in these three tasks. During their administration, the MMSE scores confirmed the initial diagnosis of mild AD for the eight impaired participants.

² Note that, in Greek, the second person plural of the personal pronoun is the formal form used to address other people.

³ Certainly the observed significant differences across pAD participants in the overall accuracy rates could be taken as an indication of variability in the patient group. However, what is relevant to the investigation of tense, agreement and aspect is not this variability, but the pAD participants' relative performance on these categories. Despite the across-patient quantitative variation, the results reveal qualitative similarities; that is, similar patterns of performance.

⁴ For a different approach to the status of subject–verb agreement as to the LF-interpretability in null subject languages, such as Greek, see Alexiadou and Anagnostopoulou (1998), and Tsimpli and Dimitrakopoulou (2007), among others. See Fyndanis et al. (2012a) for a relevant discussion.