Production and comprehension of reference of time in Swahili–English bilingual agrammatic speakers

Abstract

Background: Several studies on time reference show that monolingual agrammatic speakers have difficulty producing and/or comprehending verb forms referring to past events or actions. The PAst Discourse LInking Hypothesis (PADILIH) has been formulated to account for this phenomenon (Bastiaanse et al., 2011). In the current study on bilingual aphasia we examine whether time reference problems, especially reference to the past, extend to both languages of bilinguals with agrammatic aphasia. The two languages, Swahili and English, have different verb morphology for expressing reference of time.

Aims: The current study tested the production and comprehension of reference of time through verb morphology in two languages of Swahili–English bilingual agrammatic speakers.

Methods & Procedures: A total of 13 agrammatic speakers and 13 non-brain-damaged individuals were tested using an adaptation of the Test for Assessing Reference of Time (TART; Bastiaanse, Jonkers, & Thompson, 2008; Swahili version: Abuom & Bastiaanse, 2010). Reference to the past, present, and future conditions were examined through a sentence-completion and a picture–sentence-matching task.

Outcomes & Results: While the non-brain-damaged participants performed at ceiling in both languages, the agrammatic individuals' performance showed a selective deficit of reference to the past on both comprehension and production tasks. A similar pattern was observed in the two languages in spite of the structural differences.

Conclusions: The PAst Discourse LInking Hypothesis (PADILIH) was supported by these results. Furthermore it has been revealed that time reference deficits extend to both tested languages of bilingual speakers with agrammatic aphasia regardless of the structure of languages mastered pre-morbidly. The implications of these findings for the theories of bilingual agrammatism are discussed.

Keywords:

• Agrammatism
• Bilingual aphasia
• Time reference
• Verb inflection
• Discourse linking
• Swahili

Acknowledgments

We would like to thank Emma Shah and the administration of the Aga Khan University hospital for granting us full access to facilities at the SLT department at the hospital. We express our sincere thanks to Sanne Brederoo, Trevor Benjamin, and the three anonymous reviewers who provided very insightful and valuable comments and suggestions on the previous versions of this paper. Finally we express our gratitude to all the participants (aphasic and healthy speakers) in this study.

Notes

¹ The pre-prefix is a negation marker found in all negative sentences. However, it has not been included in the present test.

² It is not possible for a verb to possess all these affixes at the same time.

³ There was spontaneous speech available of six of the patients, who also participated in Abuom and Bastiaanse, 2012. Their speech was characterised by significantly (1) lower speech rate; (2) shorter sentences; (3) fewer grammatical sentences; (4) fewer embeddings in both Swahili and English.

⁴ The comprehension task is a binary choice test, which makes a comparison between comprehension and production based on raw scores less valid. Therefore the scores on the comprehension task were corrected for guessing, using the formula: Corrected score = #correct – [# incorrect : (#alternatives – 1)].