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Background: Individuals with aphasia after stroke (IWA) often present with working memory (WM) deficits. Research investigating the relationship between WM and language abilities has led to the promising hypothesis that treatments of WM could lead to improvements in language, a phenomenon known as transfer. Although recent treatment protocols have been successful in improving WM, the evidence to date is scarce and the extent to which improvements in trained tasks of WM transfer to untrained memory tasks, spoken sentence comprehension, and functional communication is yet poorly understood.
Aims: We aimed at (a) investigating whether WM can be improved through an adaptive n-back training in IWA (Study 1–3); (b) testing whether WM training leads to near transfer to unpracticed WM tasks (Study 1–3), and far transfer to spoken sentence comprehension (Study 1–3), functional communication (Study 2–3), and memory in daily life in IWA (Study 2–3); and (c) evaluating the methodological quality of existing WM treatments in IWA (Study 3). To address these goals, we conducted two empirical studies – a case-controls study with Hungarian speaking IWA (Study 1) and a multiple baseline study with German speaking IWA (Study 2) – and a systematic review (Study 3).
Methods: In Study 1 and 2 participants with chronic, post-stroke aphasia performed an adaptive, computerized n-back training. ‘Adaptivity’ was implemented by adjusting the tasks’ difficulty level according to the participants’ performance, ensuring that they always practiced at an optimal level of difficulty. To assess the specificity of transfer effects and to better understand the underlying mechanisms of transfer on spoken sentence comprehension, we included an outcome measure testing specific syntactic structures that have been proposed to involve WM processes (e.g., non-canonical structures with varying complexity).
Results: We detected a mixed pattern of training and transfer effects across individuals: five participants out of six significantly improved in the n-back training. Our most important finding is that all six participants improved significantly in spoken sentence comprehension (i.e., far transfer effects). In addition, we also found far transfer to functional communication (in two participants out of three in Study 2) and everyday memory functioning (in all three participants in Study 2), and near transfer to unpracticed n-back tasks (in four participants out of six). Pooled data analysis of Study 1 and 2 showed a significant negative relationship between initial spoken sentence comprehension and the amount of improvement in this ability, suggesting that the more severe the participants’ spoken sentence comprehension deficit was at the beginning of training, the more they improved after training. Taken together, we detected both near far and transfer effects in our studies, but the effects varied across participants. The systematic review evaluating the methodological quality of existing WM treatments in stroke IWA (Study 3) showed poor internal and external validity across the included 17 studies. Poor internal validity was mainly due to use of inappropriate design, lack of randomization of study phases, lack of blinding of participants and/or assessors, and insufficient sampling. Low external validity was mainly related to incomplete information on the setting, lack of use of appropriate analysis or justification for the suitability of the analysis procedure used, and lack of replication across participants and/or behaviors. Results in terms of WM, spoken sentence comprehension, and reading are promising, but further studies with more rigorous methodology and stronger experimental control are needed to determine the beneficial effects of WM intervention.
Conclusions: Results of the empirical studies suggest that WM can be improved with a computerized and adaptive WM training, and improvements can lead to transfer effects to spoken sentence comprehension and functional communication in some individuals with chronic post-stroke aphasia. The fact that improvements were not specific to certain syntactic structures (i.e., non-canonical complex sentences) in spoken sentence comprehension suggest that WM is not involved in the online, automatic processing of syntactic information (i.e., parsing and interpretation), but plays a more general role in the later stage of spoken sentence comprehension (i.e., post-interpretive comprehension). The individual differences in treatment outcomes call for future research to clarify how far these results are generalizable to the population level of IWA. Future studies are needed to identify a few mechanisms that may generalize to at least a subpopulation of IWA as well as to investigate baseline non-linguistic cognitive and language abilities that may play a role in transfer effects and the maintenance of such effects. These may require larger yet homogenous samples.
Interlocutors typically link their utterances to the discourse environment and enrich communication by linguistic (e.g., information packaging) and extra-linguistic (e.g., eye gaze, gestures) means to optimize information transfer. Psycholinguistic studies underline that ‒for meaning computation‒ listeners profit from linguistic and visual cues that draw their focus of attention to salient information. This dissertation is the first work that examines how linguistic compared to visual salience cues influence sentence comprehension using the very same experimental paradigms and materials, that is, German subject-before-object (SO) and object-before-subject (OS) sentences, across the two cue modalities. Linguistic salience was induced by indicating a referent as the aboutness topic. Visual salience was induced by implicit (i.e., unconscious) or explicit (i.e., shared) manipulations of listeners’ attention to a depicted referent.
In Study 1, a selective, facilitative impact of linguistic salience on the context-sensitive OS word order was found using offline comprehensibility judgments. More precisely, during online sentence processing, this impact was characterized by a reduced sentence-initial Late positivity which reflects reduced processing costs for updating the current mental representation of discourse. This facilitative impact of linguistic salience was not replicated by means of an implicit visual cue (Study 2) shown to modulate word order preferences during sentence production. However, a gaze shift to a depicted referent as an indicator of shared attention eased sentence-initial processing similar to linguistic salience as revealed by reduced reading times (Study 3). Yet, this cue did not modulate the strong subject-antecedent preference during later pronoun resolution like linguistic salience. Taken together, these findings suggest a significant impact of linguistic and visual salience cues on sentence comprehension, which substantiates that both the information delivered via language and via the visual environment is integrated into the mental representation of the discourse; but, the way how salience is induced is crucial to its impact.
Strings of words can correspond to more than one interpretation or underlying structure, which makes them ambiguous. Prosody can be used to resolve this structural ambiguity. This dissertation investigates the use of prosodic cues in the domains of fundamental frequency (f0) and duration to disambiguate between two interpretations of ambiguous structures when speakers addressed different interlocutors. The dissertation comprises of three production studies and one comprehension study.
Prosodic disambiguation was studied with a focus on German name sequences of three names (coordinates) in two conditions: without (Name1 and Name2 and Name3) and with internal grouping of the first two names ([Name1 and Name2] and Name3). The study of coordinates was complemented with production data of locally ambiguous sentences with a case-ambiguous first noun phrase.
Variability was studied in a controlled setting: Productions were elicited with a within-subject manipulation of context in a referential communication task in order to evoke prosodic adaptations to different conversational contexts. Context had five levels and involved interlocutors in three age groups (child, young adult, elderly adult) with German as L1 in the absence of background white noise, the young adult with background white noise, and a young adult without German as L1. Variability was explored at different levels: within a group of young individuals (intra-group level), within and between young individuals (intra-individual level and inter-individual level, respectively), and comparing between the group of young and a group of older speakers (inter-group level).
Our data replicate the use of the three prosodic cues (f0-movement, final lengthening, and pause) in productions of young adult speakers and extend their use to productions of older adult speakers. Both age groups distinguished consistently between the two coordinate conditions. Prosodic grouping in production was evident not only on the group-final Name2 but also at earlier stages in the utterance, on the group-internal Name1 (early cues). For some speakers, some listeners were able to decode these early cues effectively as they were able to reliably predict the upcoming structure after listening to Name1 only. Thus, prosodic grouping appears as a globally marked phenomenon building up along the utterance. The internal structure of coordinates was disambiguated irrespective of the conversational context. In our data, speakers only slightly modified the prosodic cues marking the disambiguation in the different contexts. Listeners were unable to identify to which interlocutor the sequence had been produced. We interpret this intra-individual consistency in the production of disambiguating prosodic cues as support for a strong link between prosody and syntax. The findings support models in favour of situational independence of disambiguating prosody. All speakers reliably marked the distinction between the grouping conditions with at least one of the three prosodic cues investigated and most of the speakers used at least two of these cues. Further, individual differences in prosodic grouping did not lead to difficulties in recovering the grouping in comprehension. Taken together, these findings support the existence of a phonological category of prosodic grouping.