Laura S. Bos

Understanding discourse-linked elements in aphasia: a threefold study in Russian

BACKGROUND Agrammatic speakers have problems with grammatical encoding and decoding. However, not all syntactic processes are equally problematic: present time reference, who questions, and reflexives can be processed by narrow syntax alone and are relatively spared compared to past time reference, which questions, and personal pronouns, respectively. The latter 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: verb morphology with reference to the past is more difficult than with reference 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 have been reported independently for different populations in different languages. The current study, for the first time, tested all conditions within the same population. AIMS We had two aims with the current study. First, we wanted to investigate whether discourse-linking is the common denominator of the deficits in time reference, wh questions, and object pronouns. Second, we aimed to compare the comprehension of discourse-linked elements in people with agrammatic and fluent aphasia. METHODS AND PROCEDURES Three sentence-picture-matching tasks were administered to 10 agrammatic, 10 fluent aphasic, and 10 non-brain-damaged Russian speakers (NBDs): (1) the Test for Assessing Reference of Time (TART) for present imperfective (reference to present) and past perfective (reference to past), (2) the Wh Extraction Assessment Tool (WHEAT) for which and who subject questions, and (3) the Reflexive-Pronoun Test (RePro) for reflexive and pronominal reference. OUTCOMES AND RESULTS NBDs scored at ceiling and significantly higher than the aphasic participants. We found an overall effect of discourse-linking in the TART and WHEAT for the agrammatic speakers, and in all three tests for the fluent speakers. Scores on the RePro were at ceiling. CONCLUSIONS The results are in line with the prediction that problems that individuals with agrammatic and fluent aphasia experience when comprehending sentences that contain verbs with past time reference, which question words and pronouns are caused by the fact that these elements involve discourse linking. The effect is not specific to agrammatism, although it may result from different underlying disorders in agrammatic and fluent aphasia.

Time reference decoupled from tense in agrammatic and fluent aphasia

Background: Reference to an event’s time frame can be accomplished through verb inflection. In agrammatic aphasia, a deficit in past time reference has been identified by Bastiaanse and colleagues (2011). In fluent aphasia, specific problems with this time frame (expressed by the past tense) have been found as well (Dragoy & Bastiaanse, 2013; Jonkers & de Bruin, 2009). However, time reference does not always coincide with tense; in languages such as Dutch and English, reference to the past can be established by using past tense (e.g., “he wrote a letter”) or a present tense auxiliary in combination with a participle, i.e., the present perfect (e.g., “he has written a letter”). Aims: The goal of this study is twofold. First, it aims to untangle tense problems from problems with past time reference through verb morphology in people with aphasia. Second, this study aims to compare the production of time reference inflection by people with agrammatic and fluent aphasia. Methods & Procedures: A sentence completion task was used to elicit reference to the non-past and past in Dutch. Reference to the past was tested through (1) a simple verb in past tense and (2) a verb complex with an auxiliary in present tense + participle (the present perfect). Reference to the non-past was tested through a simple verb in present tense. Fourteen agrammatic aphasic speakers, sixteen fluent aphasic speakers, and twenty non-brain-damaged speakers (NBDs) took part in this study. Data were analysed quantitatively and qualitatively. Outcomes & Results: NBDs scored at ceiling and significantly higher than the aphasic participants. Agrammatic speakers performed worse than fluent speakers, but the pattern of performance in both aphasic groups was similar. Reference to the past through past tense and [present tense auxiliary + participle] was more impaired than reference to the non-past. An error analysis revealed differences between the two groups. Conclusions: People with agrammatic and fluent aphasia experience problems with expressing reference to the past through verb inflection. This past time reference deficit is irrespective of the tense employed. The error patterns between the two groups reveal different underlying problems.

Gamma Oscillations as a Neural Signature of Shifting Times in Narrative Language

Verbs and other temporal expressions allow speakers to specify the location of events in time, as well as to move back and forth in time, shifting in a narrative between past, present and future. The referential flexibility of temporal expressions is well understood in linguistics but its neurocognitive bases remain unknown. We aimed at obtaining a neural signature of shifting times in narrative language. We recorded and analyzed event-related brain potentials (ERPs) and oscillatory responses to the adverb ‘now’ and to the second main verb in Punctual (‘An hour ago the boy stole a candy and now he peeled the fruit’) and Iterative (‘The entire afternoon the boy stole candy and now he peeled the fruit’) contexts. ‘An hour ago’ introduces a time frame that lies entirely in the past, ‘now’ shifts the narrative to the present, and ‘peeled’ shifts it back to the past. These two referential shifts in Punctual contexts are expected to leave very similar traces on neural responses. In contrast, ‘The entire afternoon’ specifies a time frame that may encompass past, present and future, such that both ‘now’ and ‘peeled’ are consistent with it. Here, no time shift is required. We found no difference in ERPs between Punctual and Iterative contexts either at ‘now’ or at the second verb. However, reference shifts modulated oscillatory signals. ‘Now’ and the second verb in Punctual contexts resulted in similar responses: an increase in gamma power with a left-anterior distribution. Gamma bursts were absent in Iterative contexts. We propose that gamma oscillations here reflect the binding of temporal variables to the values allowed by constraints introduced by temporal expressions in discourse.