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Individuals with agrammatic Broca's aphasia experience difficulty when processing reversible non-canonical sentences. Different accounts have been proposed to explain this phenomenon. The Trace Deletion account (Grodzinsky, 1995, 2000, 2006) attributes this deficit to an impairment in syntactic representations, whereas others (e.g., Caplan, Waters, Dede, Michaud, & Reddy, 2007; Haarmann, Just, & Carpenter, 1997) propose that the underlying structural representations are unimpaired, but sentence comprehension is affected by processing deficits, such as slow lexical activation, reduction in memory resources, slowed processing and/or intermittent deficiency, among others. We test the claims of two processing accounts, slowed processing and intermittent deficiency, and two versions of the Trace Deletion Hypothesis (TDH), in a computational framework for sentence processing (Lewis & Vasishth, 2005) implemented in ACT-R (Anderson, Byrne, Douglass, Lebiere, & Qin, 2004). The assumption of slowed processing is operationalized as slow procedural memory, so that each processing action is performed slower than normal, and intermittent deficiency as extra noise in the procedural memory, so that the parsing steps are more noisy than normal. We operationalize the TDH as an absence of trace information in the parse tree. To test the predictions of the models implementing these theories, we use the data from a German sentence—picture matching study reported in Hanne, Sekerina, Vasishth, Burchert, and De Bleser (2011). The data consist of offline (sentence-picture matching accuracies and response times) and online (eye fixation proportions) measures. From among the models considered, the model assuming that both slowed processing and intermittent deficiency are present emerges as the best model of sentence processing difficulty in aphasia. The modeling of individual differences suggests that, if we assume that patients have both slowed processing and intermittent deficiency, they have them in differing degrees.
Comprehension of non-canonical sentences can be difficult for individuals with aphasia (IWA). It is still unclear to which extent morphological cues like case marking or verb inflection may influence IWA's performance or even help to override deficits in sentence comprehension. Until now, studies have mainly used offline methods to draw inferences about syntactic deficits and, so far, only a few studies have looked at online syntactic processing in aphasia. We investigated sentence processing in German-speaking IWA by combining an offline (sentence-picture matching) and an online (eye-tracking in the visual-world paradigm) method. Our goal was to determine whether IWA are capable of using inflectional morphology (number-agreement markers on verbs and case markers in noun phrases) as a cue to sentence interpretation. We report results of two visual-world experiments using German reversible SVO and OVS sentences. In each study, there were eight IWA and 20 age-matched controls. Experiment 1 targeted the role of unambiguous case morphology, while Experiment 2 looked at processing of number-agreement cues at the verb in caseambiguous sentences. IWA showed deficits in using both types of morphological markers as a cue to non-canonical sentence interpretation and the results indicate that in aphasia, processing of case-marking cues is more vulnerable as compared to verbagreement morphology. We ascribe this finding to the higher cue reliability of agreement cues, which renders them more resistant against impairments in aphasia. However, the online data revealed that IWA are in principle capable of successfully computing morphological cues, but the integration of morphological information is delayed as compared to age-matched controls. Furthermore, we found striking differences between controls and IWA regarding subject-before-object parsing predictions. While in case-unambiguous sentences IWA showed evidence for early subjectbefore-object parsing commitments, they exhibited no straightforward subject-first prediction in case-ambiguous sentences, although controls did so for ambiguous structures. IWA delayed their parsing decisions in case-ambiguous sentences until unambiguous morphological information, such as a subject-verbnumber-agreement cue, was available. We attribute the results for IWA to deficits in predictive processes based on morphosyntactic cues during sentence comprehension. The results indicate that IWA adopt a wait-and-see strategy and initiate prediction of upcoming syntactic structure only when unambiguous case or agreement cues are available. (C) 2015 Elsevier Ltd. All rights reserved.
Background: The issue of production and perception of lexical tone in patients with brain lesions has been investigated mainly through East Asian languages and Norwegian. The present study investigated the lateralisation of lexical tone in Shona, a Bantu language. Van Lancker (1980) proposed a continuum scale of the levels of functional pitch in the speech signal. According to the functional lateralisation account (FLH), the left hemisphere (LH) is associated with highly structured pitch contrasts, such as phonological tone, whereas the right hemisphere (RH) is specialised for the least structured pitch functions cueing emotional and personal information. The extant data show that the ability to produce and identify lexical tone is frequently more impaired as a result of lesions to the LH than RH lesions.
Aims: The present investigation focused on the lateralisation of lexical tone in Shona speakers. The study sought to validate if the scale of hemispheric lateralisation as proposed by Van Lancker (1980) is also valid for Shona, a Bantu language.
Methods & Procedures: We examined five LH damaged (LHD) patients and five RH (RHD) damaged patients using a confrontational picture-naming task and a lexical tone identification task of Shona lexical tone. The first experiment investigated the ability of LHD patients and RHD patients to identify Shona lexical tone in 60 disyllabic minimal pairs. The second experiment examined the ability of Shona brain-damaged patients to produce lexical tone using a confrontational picture-naming task with 120 lexical items.
Outcomes & Results: We observed a dissociation in the performance of both the LHD and RHD patients in the two tasks. Both groups were impaired in the tone identification task relative to the non-brain-damaged controls. However, RHD patients performed significantly better than the LHD patients in the tone identification task. On the other hand, both LHD and RHD groups were equally impaired in the tone production task in comparison to the controls.
Conclusions: The discrepancy in the production and perception of Shona lexical tone for this group of brain-damaged patients shows that, although the two modes are related, they do not always get disrupted at the same level after brain damage. The results from the tone identification task suggest to a certain extent that the FLH is also valid for Shona. In order to account for all the data there is need to carefully consider alternative accounts like the acoustic cue hypothesis (Van Lancker & Sidtis, 1992).