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

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 Kaprinis, S. and Stavrakaki, S. 2007. Morphological and syntactic abilities in patients with Alzheimer's disease. Brain and Language, 103: 59–60. doi:10.1016/j.bandl.2007.07.044Crossref], Web of Science ®] , Google Scholar]; Kavé & Levy, 2003 Kavé, G. and Levy, Y. 2003. Sensitivity to gender, person and tense inflection by persons with Alzheimer's disease. Brain and Language, 87: 267–277. doi:10.1016/S0093-934X(03)00106-8Crossref], PubMed], Web of Science ®] , Google Scholar]), whereas others report morphosyntactic deficits and agrammatic profiles (e.g., Altmann, Kempler, & Andersen, 2001 Altmann, L. G. P., Kempler, D. and Andersen, E. S. 2001. Speech errors in Alzheimer's disease: Reevaluating morphosyntactic preservation. Journal of Speech, Language, and Hearing Research, 44: 1069–1082. doi:10.1044/1092-4388(2001/085)Crossref], PubMed], Web of Science ®] , Google Scholar]).

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 Baddeley, A. 1996. Exploring the central executive. The Quarterly Journal of Experimental Psychology, 49: 5–28. doi:10.1080/713755608Taylor & Francis Online], Web of Science ®] , Google Scholar]), and given the differential processing demands of agreement, tense and aspect (e.g., Fyndanis, Varlokosta, & Tsapkini, 2012a Fyndanis, V., Varlokosta, S. and Tsapkini, K. 2012a. Agrammatic production: Interpretable features and selective impairment in verb inflection. Lingua, 122: 1134–1147. doi:10.1016/j.lingua.2012.05.004Crossref], Web of Science ®] , Google Scholar]), 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 Bastiaanse, R., Bamyaci, E., Hsu, C-J., Lee, J., Yarbay Duman, T. and Thompson, C. K. 2011. Time reference in agrammatic aphasia: A cross-linguistic study. Journal of Neurolinguistics, 24: 652–673. doi:10.1016/j.jneuroling.2011.07.001Crossref], PubMed], Web of Science ®] , Google Scholar]), 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 Lapointe, S. 1985. A theory of verb form use in the speech of agrammatic aphasics. Brain and Language, 24: 100–155. doi:10.1016/0093-934X(85)90100-2Crossref], PubMed], Web of Science ®] , Google Scholar]), 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 Fyndanis, V., Varlokosta, S. and Tsapkini, K. 2012a. Agrammatic production: Interpretable features and selective impairment in verb inflection. Lingua, 122: 1134–1147. doi:10.1016/j.lingua.2012.05.004Crossref], Web of Science ®] , Google Scholar]). 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.