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There is consensus that word retrieval starts with activation of semantic representations.
However, in adults without language impairment, relatively little attention has been paid to the effects of the semantic attributes of to-be-retrieved words.
This paper, therefore, addresses the question of which item-inherent semantic factors influence word retrieval.
Specifically, it reviews the literature on a selection of these factors: imageability, concreteness, number of semantic features, typicality, intercorrelational density, featural distinctiveness, concept distinctiveness, animacy, semantic neighbourhood density, semantic similarity, operativity, valence, and arousal.
It highlights several methodological challenges in this field, and has a focus on the insights from studies with people with aphasia where the effects of these variables are more prevalent.
The paper concludes that further research simultaneously examining the effects of different semantic factors that are likely to affect lexical co-activation, and the interaction of these variables, would be fruitful, as would suitably scaled computational modelling of these effects in unimpaired language processing and in language impairment.
Such research would enable the refinement of theories of semantic processing and word production, and potentially have implications for diagnosis and treatment of semantic and lexical impairments.
It is a well-attested finding in head-initial languages that individuals with aphasia (IWA) have greater difficulties in comprehending object-extracted relative clauses (ORCs) as compared to subject-extracted relative clauses (SRCs). Adopting the linguistically based approach of Relativized Minimality (RM; Rizzi, 1990, 2004), the subject-object asymmetry is attributed to the occurrence of a Minimality effect in ORCs due to reduced processing capacities in IWA (Garraffa & Grillo, 2008; Grillo, 2008, 2009). For ORCs, it is claimed that the embedded subject intervenes in the syntactic dependency between the moved object and its trace, resulting in greater processing demands. In contrast, no such intervener is present in SRCs. Based on the theoretical framework of RM and findings from language acquisition (Belletti et al., 2012; Friedmann et al., 2009), it is assumed that Minimality effects are alleviated when the moved object and the intervening subject differ in terms of relevant syntactic features. For German, the language under investigation, the RM approach predicts that number (i.e., singular vs. plural) and the lexical restriction [+NP] feature (i.e., lexically restricted determiner phrases vs. lexically unrestricted pronouns) are considered relevant in the computation of Minimality. Greater degrees of featural distinctiveness are predicted to result in more facilitated processing of ORCs, because IWA can more easily distinguish between the moved object and the intervener.
This cumulative dissertation aims to provide empirical evidence on the validity of the RM approach in accounting for comprehension patterns during relative clause (RC) processing in German-speaking IWA. For that purpose, I conducted two studies including visual-world eye-tracking experiments embedded within an auditory referent-identification task to study the offline and online processing of German RCs. More specifically, target sentences were created to evaluate (a) whether IWA demonstrate a subject-object asymmetry, (b) whether dissimilarity in the number and/or the [+NP] features facilitates ORC processing, and (c) whether sentence processing in IWA benefits from greater degrees of featural distinctiveness. Furthermore, by comparing RCs disambiguated through case marking (at the relative pronoun or the following noun phrase) and number marking (inflection of the sentence-final verb), it was possible to consider the role of the relative position of the disambiguation point. The RM approach predicts that dissimilarity in case should not affect the occurrence of Minimality effects. However, the case cue to sentence interpretation appears earlier within RCs than the number cue, which may result in lower processing costs in case-disambiguated RCs compared to number-disambiguated RCs.
In study I, target sentences varied with respect to word order (SRC vs. ORC) and dissimilarity in the [+NP] feature (lexically restricted determiner phrase vs. pronouns as embedded element). Moreover, by comparing the impact of these manipulations in case- and number-disambiguated RCs, the effect of dissimilarity in the number feature was explored. IWA demonstrated a subject-object asymmetry, indicating the occurrence of a Minimality effect in ORCs. However, dissimilarity neither in the number feature nor in the [+NP] feature alone facilitated ORC processing. Instead, only ORCs involving distinct specifications of both the number and the [+NP] features were well comprehended by IWA. In study II, only temporarily ambiguous ORCs disambiguated through case or number marking were investigated, while controlling for varying points of disambiguation. There was a slight processing advantage of case marking as cue to sentence interpretation as compared to number marking.
Taken together, these findings suggest that the RM approach can only partially capture empirical data from German IWA. In processing complex syntactic structures, IWA are susceptible to the occurrence of the intervening subject in ORCs. The new findings reported in the thesis show that structural dissimilarity can modulate sentence comprehension in aphasia. Interestingly, IWA can override Minimality effects in ORCs and derive correct sentence meaning if the featural specifications of the constituents are maximally different, because they can more easily distinguish the moved object and the intervening subject given their reduced processing capacities. This dissertation presents new scientific knowledge that highlights how the syntactic theory of RM helps to uncover selective effects of morpho-syntactic features on sentence comprehension in aphasia, emphasizing the close link between assumptions from theoretical syntax and empirical research.
Individuals with aphasia vary in the speed and accuracy they perform sentence comprehension tasks. Previous results indicate that the performance patterns of individuals with aphasia vary between tasks (e.g., Caplan, DeDe, & Michaud, 2006; Caplan, Michaud, & Hufford, 2013a). Similarly, it has been found that the comprehension performance of individuals with aphasia varies between homogeneous test sentences within and between sessions (e.g., McNeil, Hageman, & Matthews, 2005). These studies ascribed the variability in the performance of individuals with aphasia to random noise. This conclusion would be in line with an influential theory on sentence comprehension in aphasia, the resource reduction hypothesis (Caplan, 2012). However, previous studies did not directly compare variability in language-impaired and language-unimpaired adults. Thus, it is still unclear how the variability in sentence comprehension differs between individuals with and without aphasia. Furthermore, the previous studies were exclusively carried out in English. Therefore, the findings on variability in sentence processing in English still need to be replicated in a different language.
This dissertation aims to give a systematic overview of the patterns of variability in sentence comprehension performance in aphasia in German and, based on this overview, to put the resource reduction hypothesis to the test. In order to reach the first aim, variability was considered on three different dimensions (persons, measures, and occasions) following the classification by Hultsch, Strauss, Hunter, and MacDonald (2011). At the dimension of persons, the thesis compared the performance of individuals with aphasia and language-unimpaired adults. At the dimension of measures, this work explored the performance across different sentence comprehension tasks (object manipulation, sentence-picture matching). Finally, at the dimension of occasions, this work compared the performance in each task between two test sessions. Several methods were combined to study variability to gain a large and diverse database. In addition to the offline comprehension tasks, the self-paced-listening paradigm and the visual world eye-tracking paradigm were used in this work.
The findings are in line with the previous results. As in the previous studies, variability in sentence comprehension in individuals with aphasia emerged between test sessions and between tasks. Additionally, it was possible to characterize the variability further using hierarchical Bayesian models. For individuals with aphasia, it was shown that both between-task and between-session variability are unsystematic. In contrast to that, language-unimpaired individuals exhibited systematic differences between measures and between sessions. However, these systematic differences occurred only in the offline tasks. Hence, variability in sentence comprehension differed between language-impaired and language-unimpaired adults, and this difference could be narrowed down to the offline measures.
Based on this overview of the patterns of variability, the resource reduction hypothesis was evaluated. According to the hypothesis, the variability in the performance of individuals with aphasia can be ascribed to random fluctuations in the resources available for sentence processing. Given that the performance of the individuals with aphasia varied unsystematically, the results support the resource reduction hypothesis. Furthermore, the thesis proposes that the differences in variability between language-impaired and language-unimpaired adults can also be explained by the resource reduction hypothesis. More specifically, it is suggested that the systematic changes in the performance of language-unimpaired adults are due to decreasing fluctuations in available processing resources. In parallel, the unsystematic variability in the performance of individuals with aphasia could be due to constant fluctuations in available processing resources. In conclusion, the systematic investigation of variability contributes to a better understanding of language processing in aphasia and thus enriches aphasia research.
The present study aims to contribute to the ongoing discussion about the impact of discourse-linking deficits on the performance of individuals with aphasia by providing new data from a set of rarely investigated constructions: sentences in which a clitic pronoun coexists alongside with the full DP it agrees with. To do so, we use data of individuals with non-fluent aphasias who need to overcome the difficulties in direct object (accusative) clitic production. This results in overproduction of non-target clitic right dislocations (RDs) and clitic doubling (CD). Data from 15 individual’s native speakers of Spanish and Catalan are discussed. Data complement the results of previous investigations on discourse-linking effects in these languages, allowing the interpretation of results across constructions.
It is well-known that individuals with aphasia (IWA) have difficulties understanding sentences that involve non-adjacent dependencies, such as object relative clauses or passives (Caplan, Baker, & Dehaut, 1985; Caramazza & Zurif, 1976). A large body of research supports the view that IWA’s grammatical system is intact, and that comprehension difficulties in aphasia are caused by a processing deficit, such as a delay in lexical access and/or in syntactic structure building (e.g., Burkhardt, Piñango, & Wong, 2003; Caplan, Michaud, & Hufford, 2015; Caplan, Waters, DeDe, Michaud, & Reddy, 2007; Ferrill, Love, Walenski, & Shapiro, 2012; Hanne, Burchert, De Bleser, & Vasishth, 2015; Love, Swinney, Walenski, & Zurif, 2008). The main goal of this dissertation is to computationally investigate the processing sources of comprehension impairments in sentence processing in aphasia.
In this work, prominent theories of processing deficits coming from the aphasia literature are implemented within two cognitive models of sentence processing –the activation-based model (Lewis & Vasishth, 2005) and the direct-access model (McEl- ree, 2000)–. These models are two different expressions of the cue-based retrieval theory (Lewis, Vasishth, & Van Dyke, 2006), which posits that sentence processing is the result of a series of iterative retrievals from memory. These two models have been widely used to account for sentence processing in unimpaired populations in multiple languages and linguistic constructions, sometimes interchangeably (Parker, Shvarts- man, & Van Dyke, 2017). However, Nicenboim and Vasishth (2018) showed that when both models are implemented in the same framework and fitted to the same data, the models yield different results, because the models assume different data- generating processes. Specifically, the models hold different assumptions regarding the retrieval latencies. The second goal of this dissertation is to compare these two models of cue-based retrieval, using data from individuals with aphasia and control participants. We seek to answer the following question: Which retrieval mechanism is more likely to mediate sentence comprehension?
We model 4 subsets of existing data: Relative clauses in English and German; and control structures and pronoun resolution in German. The online data come from either self-paced listening experiments, or visual-world eye-tracking experiments. The offline data come from a complementary sentence-picture matching task performed at the end of the trial in both types of experiments. The two competing models of retrieval are implemented in the Bayesian framework, following Nicenboim and Vasishth (2018). In addition, we present a modified version of the direct-acess model that – we argue – is more suitable for individuals with aphasia.
This dissertation presents a systematic approach to implement and test verbally- stated theories of comprehension deficits in aphasia within cognitive models of sen- tence processing. The conclusions drawn from this work are that (a) the original direct-access model (as implemented here) cannot account for the full pattern of data from individuals with aphasia because it cannot account for slow misinterpretations; and (b) an activation-based model of retrieval can account for sentence comprehension deficits in individuals with aphasia by assuming a delay in syntactic structure building, and noise in the processing system. The overall pattern of results support an activation-based mechanism of memory retrieval, in which a combination of processing deficits, namely slow syntax and intermittent deficiencies, cause comprehension difficulties in individuals with aphasia.
Purpose: The existing body of work regarding discourse coherence in aphasia has provided mixed results, leaving the question of coherence being impaired or intact as a result of brain injury unanswered. In this study, discourse coherence in non-brain-damaged (NBD) speakers and speakers with anomic aphasia was investigated quantitatively and qualitatively. Method: Fifteen native speakers of Cantonese with anomic aphasia and 15 NBD participants produced 60 language samples. Elicitation tasks included story-telling induced by a picture series and a procedural description. The samples were annotated for discourse structure in the framework of Rhetorical Structure Theory (RST) in order to analyse a number of structural parameters. After that 20 naive listeners rated coherence of each sample. Result: Disordered discourse was rated as significantly less coherent. The NBD group demonstrated a higher production fluency than the participants with aphasia and used a richer set of semantic relations to create discourse, particularly in the description of settings, expression of causality, and extent of elaboration. People with aphasia also tended to omit essential information content. Conclusion: Reduced essential information content, lower degree of elaboration, and a larger amount of structural disruptions may have contributed to the reduced overall discourse coherence in speakers with anomic aphasia.
Time reference, which has been found to be selectively impaired in agrammatic aphasia, is often interwoven with grammatical aspect. A recent study on Russian aphasia found that time reference and aspect interact: Past reference was less impaired when tested within a perfective aspect context (compared to when tested within an imperfective aspect context), and reference to the non-past was less impaired when tested within an imperfective aspect context (compared to when tested within a perfective aspect context). To explain this pattern, the authors argued that there are prototypical associations between time frames and aspectual values. The present study explores the relationship between time reference and aspect focusing on Greek aphasia and healthy ageing and using a sentence completion task that crosses time reference and aspect. The findings do not support prototypical matches between different time frames and aspectual values. Building on relevant studies, we propose that patterns of performance of healthy or language-impaired speakers on constrained tasks tapping different combinations of time frames with aspectual values should reflect the relative frequency of these combinations in a given language. The analysis of the results at the individual level revealed a double dissociation, which indicates that a given time frame-aspectual value combination may be relatively easy to process for some persons with aphasia but demanding for some others.
Discourse production in aphasia: a current review of theoretical and methodological challenges
(2016)
Background: Discourse abilities play an important role in the assessment, classification, and therapy outcome evaluation of people with aphasia. Discourse production in aphasia has been studied quite extensively in the last 15 years. Nevertheless, many questions still do not have definitive answers.Aims: The aim of this review is to present the current situation in the research on a number of crucial aspects of discourse production in aphasia, focusing on methodological progress and related challenges. This review continues the discussion of the core themes in the field, aiming to render it as up-to-date as possible.Main Contribution: The review focuses on a number of unexplored theoretical issues, specifically, the interface between micro- and macrolinguistic abilities, and the relationship between linguistic competence and communicative success in aphasia. The emphasis on theoretical challenges, along with the thorough discussion of methodological problems in the field, makes this review a starting point and a comprehensive information source for researchers planning to address language production in people with aphasia.Conclusion: Although the picture is not yet complete, recent advancements lead to a better understanding of the processes involved in aphasic discourse production. Different approaches provide insights into the complex multifaceted nature of discourse-level phenomena; however, methodological issues, including low comparability, substantially slow down the progress in the field.
Background: Word retrieval in aphasia involves different levels of processinglemma retrieval, grammatical encoding, lexeme retrieval, and phonological encodingbefore articulation can be programmed and executed. Several grammatical, semantic, lexical, and phonological characteristics, such as word class, age of acquisition, imageability, and word frequency influence the degree of success in word retrieval. It is, however, not yet clear how these factors interact. The current study focuses on the retrieval of nouns and verbs in isolation and in sentence context and evaluates the impact of the mentioned factors on the performance of a group of 54 aphasic speakers.Aims: The main aim is to measure the effect of word frequency on the retrieval of nouns and verb by disentangling the influence of word class, age of acquisition, imageability, and lemma and lexeme frequencies on word retrieval in aphasia.Methods & Procedures: Four tests for retrieval of nouns, verbs in isolation, and infinitives and finite verbs were administered to 54 aphasic speakers. The influence of lemma and lexeme frequency, Age of Acquisition on the word retrieval abilities was analysed.Outcomes and Results: Word class, age of acquisition, and imageability play a significant role in the retrieval of nouns and verbs: nouns are easier than verbs; the earlier a word has been learned and the more concrete it is, the easier it is to retrieve. When performance is controlled for these factors, lemma frequency turns out to play a minor role: only in object naming does it affect word retrieval: the higher the lemma frequency of a noun, the easier it is to access. Such an effect does not exist for verbs, neither on an action-naming test, nor when verbs have to be retrieved in sentence context. Lexeme frequency was not found to be a better predictor than lemma frequency in predicting word retrieval in aphasia.Conclusions: Word retrieval in aphasia is influenced by grammatical, semantic, and lexical factors. Word frequency only plays a minor role: it affects the retrieval of nouns, but not of verbs.
Discourse production is crucial for communicative success and is in the core of aphasia assessment and treatment. Coherence differentiates discourse from a series of utterances/sentences; it is internal unity and connectedness, and, as such, perhaps the most inherent property of discourse. It is unclear whether people with aphasia, who experience various language production difficulties, preserve the ability to produce coherent discourse. A more general question of how coherence is established and represented linguistically has been addressed in the literature, yet remains unanswered. This dissertation presents an investigation of discourse production in aphasia and the linguistic mechanisms of establishing coherence.