Syntactic processing in aphasia

Grammatical Parallelism in Aphasia: A Lesion-Symptom Mapping Study

Sentence structure, or syntax, is potentially a uniquely creative aspect of the human mind. Neuropsychological experiments in the 1970s suggested parallel syntactic production and comprehension deficits in agrammatic Broca's aphasia, thought to result from damage to syntactic mechanisms in Broca's area in the left frontal lobe. This hypothesis was sometimes termed overarching agrammatism, converging with developments in linguistic theory concerning central syntactic mechanisms supporting language production and comprehension. However, the evidence supporting an association among receptive syntactic deficits, expressive agrammatism, and damage to frontal cortex is equivocal. In addition, the relationship among a distinct grammatical production deficit in aphasia, paragrammatism, and receptive syntax has not been assessed. We used lesion-symptom mapping in three partially overlapping groups of left-hemisphere stroke patients to investigate these issues: grammatical production deficits in a primary group of 53 subjects and syntactic comprehension in larger sample sizes (N = 130, 218) that overlapped with the primary group. Paragrammatic production deficits were significantly associated with multiple analyses of syntactic comprehension, particularly when incorporating lesion volume as a covariate, but agrammatic production deficits were not. The lesion correlates of impaired performance of syntactic comprehension were significantly associated with damage to temporal lobe regions, which were also implicated in paragrammatism, but not with the inferior and middle frontal regions implicated in expressive agrammatism. Our results provide strong evidence against the overarching agrammatism hypothesis. By contrast, our results suggest the possibility of an alternative grammatical parallelism hypothesis rooted in paragrammatism and a central syntactic system in the posterior temporal lobe.

Brain Damage Associated with Impaired Sentence Processing in Acute Aphasia

Left-hemisphere brain damage commonly affects patients' abilities to produce and comprehend syntactic structures, a condition typically referred to as "agrammatism." The neural correlates of agrammatism remain disputed in the literature, and distributed areas have been implicated as important predictors of performance, for example, Broca's area, anterior temporal areas, and temporo-parietal areas. We examined the association between damage to specific language-related ROIs and impaired syntactic processing in acute aphasia. We hypothesized that damage to the posterior middle temporal gyrus, and not Broca's area, would predict syntactic processing abilities. One hundred four individuals with acute aphasia (<20 days poststroke) were included in the study. Structural MRI scans were obtained, and all participants completed a 45-item sentence-picture matching task. We performed an ROI-based stepwise regression analyses to examine the relation between cortical brain damage and impaired comprehension of canonical and noncanonical sentences. Damage to the posterior middle temporal gyrus was the strongest predictor for overall task performance and performance on noncanonical sentences. Damage to the angular gyrus was the strongest predictor for performance on canonical sentences, and damage to the posterior superior temporal gyrus predicted noncanonical scores when performance on canonical sentences was included as a cofactor. Overall, our models showed that damage to temporo-parietal and posterior temporal areas was associated with impaired syntactic comprehension. Our results indicate that the temporo-parietal area is crucially implicated in complex syntactic processing, whereas the role of Broca's area may be complementary.

Neurocognitive Recovery of Sentence Processing in Aphasia

Purpose Reorganization of language networks in aphasia takes advantage of the facts that (a) the brain is an organ of plasticity, with neuronal changes occurring throughout the life span, including following brain damage; (b) plasticity is highly experience dependent; and (c) as with any learning system, language reorganization involves a synergistic interplay between organism-intrinsic (i.e., cognitive and brain) and organism-extrinsic (i.e., environmental) variables. A major goal for clinical treatment of aphasia is to be able to prescribe treatment and predict its outcome based on the neurocognitive deficit profiles of individual patients. This review article summarizes the results of research examining the neurocognitive effects of psycholinguistically based treatment (i.e., Treatment of Underlying Forms; Thompson & Shapiro, 2005) for sentence processing impairments in individuals with chronic agrammatic aphasia resulting from stroke and primary progressive aphasia and addresses both behavioral and brain variables related to successful treatment outcomes. The influences of lesion volume and location, perfusion (blood flow), and resting-state neural activity on language recovery are also discussed as related to recovery of agrammatism and other language impairments. Based on these and other data, principles for promoting neuroplasticity of language networks are presented. Conclusions Sentence processing treatment results in improved comprehension and production of complex syntactic structures in chronic agrammatism and generalization to less complex, linguistically related structures in chronic agrammatism. Patients also show treatment-induced shifts toward normal-like online sentence processing routines (based on eye movement data) and changes in neural recruitment patterns (based on functional neuroimaging), with posttreatment activation of regions overlapping with those within sentence processing and dorsal attention networks engaged by neurotypical adults performing the same task. These findings provide compelling evidence that treatment focused on principles of neuroplasticity promotes neurocognitive recovery in chronic agrammatic aphasia. Presentation Videohttps://doi.org/10.23641/asha.10257587.

Verbal short-term memory capacities and executive function in semantic and syntactic interference resolution during sentence comprehension: Evidence from aphasia

This study examined the role of verbal short-term memory (STM) and executive function (EF) underlying semantic and syntactic interference resolution during sentence comprehension for persons with aphasia (PWA) with varying degrees of STM and EF deficits. Semantic interference was manipulated by varying the semantic plausibility of the intervening NP as subject of the verb and syntactic interference was manipulated by varying whether the NP was another subject or an object. Nine PWA were assessed on sentence reading times and on comprehension question performance. PWA showed exaggerated semantic and syntactic interference effects relative to healthy age-matched control subjects. Importantly, correlational analyses showed that while answering comprehension questions, PWA' semantic STM capacity related to their ability to resolve semantic but not syntactic interference. In contrast, PWA' EF abilities related to their ability to resolve syntactic but not semantic interference. Phonological STM deficits were not related to the ability to resolve either type of interference. The results for semantic interference are consistent with prior findings indicating a role for semantic but not phonological STM in sentence comprehension, specifically with regard to maintaining semantic information prior to integration. The results for syntactic interference are consistent with the recent findings suggesting that EF is critical for syntactic processing.

Proform-Antecedent Linking in Individuals with Agrammatic Aphasia: A Test of the Intervener Hypothesis

PURPOSE

To evaluate processing and comprehension of pronouns and reflexives in individuals with agrammatic (Broca's) aphasia and age-matched control participants. Specifically, we evaluate processing and comprehension patterns in terms of a specific hypothesis -- the Intervener Hypothesis - that posits that the difficulty of individuals with agrammatic (Broca's) aphasia results from similarity-based interference caused by the presence of an intervening NP between two elements of a dependency chain.

METHODS

We used an eye tracking-while-listening paradigm to investigate real-time processing (Experiment 1) and a sentence-picture matching task to investigate final interpretive comprehension (Experiment 2) of sentences containing proforms in complement phrase and subject relative constructions.

RESULTS

Individuals with agrammatic aphasia demonstrated a greater proportion of gazes to the correct referent of reflexives relative to pronouns and significantly greater comprehension accuracy of reflexives relative to pronouns.

CONCLUSIONS

These results provide support for the Intervener Hypothesis, previous support for which comes from studies of Wh- questions and unaccusative verbs, and we argue that this account provides an explanation for the deficits of individuals with agrammatic aphasia across a growing set of sentence constructions. The current study extends this hypothesis beyond filler-gap dependencies to referential dependencies and allows us to refine the hypothesis in terms of the structural constraints that meet the description of the Intervener Hypothesis.

The Localization of Long-Distance Dependency Components: Integrating the Focal-lesion and Neuroimaging Record

In the sentence “The captain who the sailor greeted is tall,” the connection between the relative pronoun and the object position of greeted represents a long-distance dependency (LDD), necessary for the interpretation of “the captain” as the individual being greeted. Whereas the lesion-based record shows preferential involvement of only the left inferior frontal (LIF) cortex, associated with Broca's aphasia, during real-time comprehension of LDDs, the neuroimaging record shows additional involvement of the left posterior superior temporal (LPST) and lower parietal cortices, which are associated with Wernicke's aphasia. We test the hypothesis that this localization incongruence emerges from an interaction of memory and linguistic constraints involved in the real-time implementation of these dependencies and which had not been previously isolated. Capitalizing on a long-standing psycholinguistic understanding of LDDs as the workings of an active filler, we distinguish two linguistically defined mechanisms: GAP-search, triggered by the retrieval of the relative pronoun, and GAP-completion, triggered by the retrieval of the embedded verb. Each mechanism is hypothesized to have distinct memory demands and given their distinct linguistic import, potentially distinct brain correlates. Using fMRI, we isolate the two mechanisms by analyzing their relevant sentential segments as separate events. We manipulate LDD-presence/absence and GAP-search type (direct/indirect) reflecting the absence/presence of intervening islands. Results show a direct GAP-search—LIF cortex correlation that crucially excludes the LPST cortex. Notably, indirect GAP-search recruitment is confined to supplementary-motor and lower-parietal cortex indicating that GAP presence alone is not enough to engage predictive functions in the LIF cortex. Finally, GAP-completion shows recruitment implicating the dorsal pathway including: the supplementary motor cortex, left supramarginal cortex, precuneus, and anterior/dorsal cingulate. Altogether, the results are consistent with previous findings connecting GAP-search, as we define it, to the LIF cortex. They are not consistent with an involvement of the LPST cortex in any of the two mechanisms, and therefore support the view that the LPST cortex is not crucial to LDD implementation. Finally, results support neurocognitive architectures that involve the dorsal pathway in LDD resolution and that distinguish the memory commitments of the LIF cortex as sensitive to specific language-dependent constraints beyond phrase-structure building considerations.

Mechanisms underlying syntactic comprehension deficits in vascular aphasia: new evidence from self-paced listening

Sixty-one people with aphasia (pwa) and 41 matched controls were tested for the ability to understand sentences that required the ability to process particular syntactic elements and assign particular syntactic structures. Participants paced themselves word-by-word through 20 examples of 11 spoken sentence types and indicated which of two pictures corresponded to the meaning of each sentence. Sentences were developed in pairs such that comprehension of the experimental version of a pair required an aspect of syntactic processing not required in the corresponding baseline sentence. The need for the syntactic operations required only in the experimental version was triggered at a "critical word" in the experimental sentence. Listening times for critical words in experimental sentences were compared to those for corresponding words in the corresponding baseline sentences. The results were consistent with several models of syntactic comprehension deficits in pwa: resource reduction, slowed lexical and/or syntactic processing, abnormal susceptibility to interference from thematic roles generated non-syntactically. They suggest that a previously unidentified disturbance limiting the duration of parsing and interpretation may lead to these deficits, and that this mechanism may lead to structure-specific deficits in pwa. The results thus point to more than one mechanism underlying syntactic comprehension disorders both across and within pwa.

Preservation of passive constructions in a patient with primary progressive aphasia

Research into agrammatic comprehension in English has described a pattern of impaired understanding of passives and retained ability on active constructions. Some accounts of this dissociation predict that patients who are unable to comprehend actives will also be impaired in the comprehension of passives. We report the case of a man with primary progressive aphasia (PPA) (WR), whose comprehension was at chance on active sentences, but at ceiling on passives. In a series of reversible sentence comprehension tests WR displayed difficulties with active transitives and truncated actives with an auxiliary. In passive sentences, he displayed sensitivity to the agent marker by, as well as the passive morphology of the verb. This pattern of dissociation challenges current theories of agrammatic comprehension. We explore explanations based on the distinction between morphological and configurational cues, as well as on the semantic and discourse related differences between active and passive constructions.

Damage to left anterior temporal cortex predicts impairment of complex syntactic processing: a lesion-symptom mapping study

Sentence processing problems form a common consequence of left-hemisphere brain injury, in some patients to such an extent that their pattern of language performance is characterized as "agrammatic". However, the location of left-hemisphere damage that causes such problems remains controversial. It has been suggested that the critical site for syntactic processing is Broca's area of the frontal cortex or, alternatively, that a more widely distributed network is responsible for syntactic processing. The aim of this study was to identify brain regions that are required for successful sentence processing. Voxel-based lesion-symptom mapping (VLSM) was used to identify brain regions where injury predicted impaired sentence processing in 50 native speakers of Icelandic with left-hemisphere stroke. Sentence processing was assessed by having individuals identify which picture corresponded to a verbally presented sentence. The VLSM analysis revealed that impaired sentence processing was best predicted by damage to a large left-hemisphere temporo-parieto-occipital area. This is likely due to the multimodal nature of the sentence processing task, which involves auditory and visual analysis, as well as lexical and syntactic processing. Specifically impaired processing of noncanonical sentence types, when compared with canonical sentence processing, was associated with damage to the left-hemisphere anterior superior and middle temporal gyri and the temporal pole. Anterior temporal cortex, therefore, appears to play a crucial role in syntactic processing, and patients with brain damage to this area are more likely to present with receptive agrammatism than patients in which anterior temporal cortex is spared.

Broca's area and sentence comprehension: a relationship parasitic on dependency, displacement or predictability?

The current rapid event-related fMRI study used optional parasitic-gap constructions, such as [Which paper] did the tired student submit [(gap)--] after reviewing [(p-gap)--/it]?, to test 3 potential roles for Broca's area in sentence processing. These 3 functional options are: I. any intra-sentential Dependency relation activates Broca's area. II. This region specifically processes syntactic Displacement or movement. III. Broca's area handles any dependency relation, as long as it is predictable at an early stage of processing. Broca's area was only activated by the contrast that tested predictability within BA 45, as determined by its overlap with cytoarchitectonic probability maps. These results imply that an alternative or modified functional account of Broca's area, from those presently available, is required. Constraints on either a displacement account to movements that are not parasitic or a Working Memory one to predicted dependencies that cross verbal arguments or noun phrases would achieve the necessary consistency. Further, the results from the minimal contrasts investigating displacement and dependency have implications to potential language regions outside of Broca's area. The minimal contrast investigating displacement activated the left anterior Middle Temporal Gyrus, which has more recently been claimed to play a role in syntactic operations.

The picture of the linguistic brain: how sharp can it be? Reply to Fedorenko & Kanwisher

What is the best way to learn how the brain analyzes linguistic input? Two popular methods have attempted to segregate and localize linguistic processes: analyses of language deficits subsequent to (mostly focal) brain disease, and functional Magnetic Resonance Imaging (fMRI) in health. A recent Compass article by Fedorenko and Kanwisher (FK, 2009) observes that these methods group together data from many individuals through methods that rely on variable anatomical landmarks, and that results in a murky picture of how language is represented in the brain. To get around the variability problem, FK propose to import into neurolinguistics a method that has been successfully used in vision research - one that locates functional Regions Of Interest (fROIs) in each individual brain.In this note, I propose an alternative perspective. I first take issue with FK's reading of the literature. I point out that, when the neurolinguistic landscape is examined with the right linguistic spectacles, the emerging picture - while intriguingly complex - is not murky, but rather, stable and clear, parsing the linguistic brain into functionally and anatomically coherent pieces. I then examine the potential value of the method that FK propose, in light of important micro-anatomical differences between language and high-level vision areas, and conclude that as things stand the method they propose is not very likely to bear much fruit in neurolinguistic research.

Binding in agrammatic aphasia: Processing to comprehension

BACKGROUND: Theories of comprehension deficits in Broca's aphasia have largely been based on the pattern of deficit found with movement constructions. However, some studies have found comprehension deficits with binding constructions, which do not involve movement. AIMS: This study investigates online processing and offline comprehension of binding constructions, such as reflexive (e.g., himself) and pronoun (e.g., him) constructions in unimpaired and aphasic individuals in an attempt to evaluate theories of agrammatic comprehension. METHODS #ENTITYSTARTX00026; PROCEDURES: Participants were eight individuals with agrammatic Broca's aphasia and eight age-matched unimpaired individuals. We used eyetracking to examine online processing of binding constructions while participants listened to stories. Offline comprehension was also tested. OUTCOMES #ENTITYSTARTX00026; RESULTS: The eye movement data showed that individuals with Broca's aphasia were able to automatically process the correct antecedent of reflexives and pronouns. In addition, their syntactic processing of binding was not delayed compared to normal controls. Nevertheless, offline comprehension of both pronouns and reflexives was significantly impaired compared to the control participants. This comprehension failure was reflected in the aphasic participants' eye movements at sentence end, where fixations to the competitor increased. CONCLUSIONS: These data suggest that comprehension difficulties with binding constructions seen in agrammatic aphasic patients are not due to a deficit in automatic syntactic processing or delayed processing. Rather, they point to a possible deficit in lexical integration.

Automatic processing of wh- and NP-movement in agrammatic aphasia: Evidence from eyetracking

Individuals with agrammatic Broca's aphasia show deficits in comprehension of non-canonical wh-movement and NP-movement sentences. Previous work using eyetracking has found that agrammatic and unimpaired listeners show very similar patterns of automatic processing for wh-movement sentences. The current study attempts to replicate this finding for sentences with wh-movement (in object relatives in the current study) and to extend it to sentences with NP movement (passives). For wh-movement sentences, aphasic and control participants' eye-movements differed most dramatically in late regions of the sentence and post-offset, with aphasic participants exhibiting lingering attention to a salient but grammatically impermissible competitor. The eye-movement differences between correct and incorrect trials for wh-movement sentences were similar, with incorrect trials also exhibiting competition from an impermissible interpretation late in the sentence. Furthermore, the two groups exhibited similar eye-movement patterns in response to passive NP-movement sentences, but showed little evidence of gap-filling for passives. The results suggest that aphasic and unimpaired individuals may generate similar representations during comprehension, but that aphasics are highly vulnerable to interference from alternative interpretations (Ferreira, 2003).

Pronominal resolution and gap filling in agrammatic aphasia: evidence from eye movements

This paper reports the results of three studies examining comprehension and real-time processing of pronominal (Experiment 1) and Wh-movement (Experiments 2 and 3) structures in agrammatic and unimpaired speakers using eyetracking. We asked the following questions: (a) Is off-line comprehension of these constructions impaired in agrammatic listeners?, (b) Do agrammatic, like unimpaired, listeners show eye movement patterns indicative of automatic pronominal reference resolution and/or gap-filling?, and (c) Do eyetracking patterns differ when sentences are correctly versus incorrectly interpreted, or do automatic processes prevail in spite of comprehension failure? Results showed that off-line comprehension of both pronoun and Wh-movement structures was impaired in our agrammatic cohort. However, the aphasic participants showed visual evidence of real-time reference resolution as they processed binding structures, including both pronouns and reflexives, as did our unimpaired control participants. Similarly, both the patients and the control participants showed patterns consistent with successful gap filling during processing of Wh-movement structures. For neither pronominal nor movement structures did we find evidence of delayed processing. Notably, these patterns were found for the aphasic participants even when they incorrectly interpreted target sentences, with the exception of object relative constructions. For incorrectly interpreted sentences, we found end of sentence lexical competition effects. These findings indicate that aberrant lexical integration, rather than representational deficits or generally slowed processing, may underlie agrammatic aphasic listener's comprehension failure.

Working memory and syntax interact in Broca's area

Comprehension of filler-gap dependency relations (as in this is the man who the woman is touching) is supported by Broca's area. There are two views regarding the processing role of this brain region in comprehending these dependencies. Specifists hold that Broca's area plays a specific syntactic role in processing filler-gaps. Generalists maintain that as the on-line linking of fillers and gaps taxes Working Memory (WM) resources, Broca's area supports a domain general WM. The current fMRI study tested these two views in a grammaticality judgment task, where participants were presented with two syntactically distinct dependency relations: (a) Filler-Gap and (b) Reflexive Binding. The distance between the dependent elements within each of the constructions was varied, to parametrically vary WM demands. The Generalists would expect parametric variation of distance in both dependencies to lead to a linear increase in activation of Broca's area. Our results support the specifists' view, however: the left inferior frontal gyrus demonstrated an interaction between distance and dependency type with a positive linear effect only for Filler-Gaps. A positive linear effect of distance across both dependencies was only found in the bilateral parahippocampal/fusiform gyri. Therefore the role of Broca's area in WM is syntactically specific to filler-gap relations.

Brain responses to filled gaps

An unresolved issue in the study of sentence comprehension is whether the process of gap-filling is mediated by the construction of empty categories (traces), or whether the parser relates fillers directly to the associated verb's argument structure. We conducted an event-related potentials (ERP) study that used the violation paradigm to examine the time course and spatial distribution of brain responses to ungrammatically filled gaps. The results indicate that the earliest brain response to the violation is an early left anterior negativity (eLAN). This ERP indexes an early phase of pure syntactic structure building, temporally preceding ERPs that reflect semantic integration and argument structure satisfaction. The finding is interpreted as evidence that gap-filling is mediated by structurally predicted empty categories, rather than directly by argument structure operations.

The speed of lexical activation is altered in Parkinson's disease

Disturbed comprehension of complex noncanonical sentences in Parkinson's disease (PD) has been linked to dopamine depletion and delayed lexical retrieval. The aim of the present study was to replicate findings of delayed lexical activation in PD patients with noncanonical sentence processing difficulties, and investigate the influence of dopamine depletion on these changes to lexical access. In the first experiment, 20 patients with PD (tested whilst 'on' dopaminergic medication) and 23 controls participated in a list priming experiment. In this paradigm, stimuli are presented as a continuous list of words/nonwords, and semantic priming effects were measured across inter-stimulus intervals (ISIs) of 500 ms, 1000 ms and 1500 ms, with data analyzed using multivariate analyses of variance. The results revealed longer delays in lexical activation for PD patients with poor comprehension of noncanonical sentences, suggesting that the speed of lexical access may be compromised in PD, and that this feature may contribute to certain sentencecomprehension difficulties. In the second experiment, 7 patients with PD who participated in the first experiment, performed the same lexical decision task while 'off' their dopaminergic medication. Semantic priming effects were measured across ISIs of 500 ms and 1500 ms. Within group comparisons revealed a different pattern of semantic priming for the PD patients when 'on' compared to 'off' medication, providing further support for a dopaminergic influence on the speed of information processing and lexical activation.

Real-time comprehension of wh- movement in aphasia: evidence from eyetracking while listening

Sentences with non-canonical wh- movement are often difficult for individuals with agrammatic Broca's aphasia to understand (, inter alia). However, the explanation of this difficulty remains controversial, and little is known about how individuals with aphasia try to understand such sentences in real time. This study uses an eyetracking while listening paradigm to examine agrammatic aphasic individuals' on-line comprehension of movement sentences. Participants' eye-movements were monitored while they listened to brief stories and looked at visual displays depicting elements mentioned in the stories. The stories were followed by comprehension probes involving wh- movement. In line with previous results for young normal listeners [Sussman, R. S., & Sedivy, J. C. (2003). The time-course of processing syntactic dependencies: evidence from eye movements. Language and Cognitive Processes, 18, 143-161], the study finds that both older unimpaired control participants (n=8) and aphasic individuals (n=12) showed visual evidence of successful automatic comprehension of wh- questions (like "Who did the boy kiss that day at school?"). Specifically, both groups fixated on a picture corresponding to the moved element ("who," the person kissed in the story) at the position of the verb. Interestingly, aphasic participants showed qualitatively different fixation patterns for trials eliciting correct and incorrect responses. Aphasic individuals looked first to the moved-element picture and then to a competitor following the verb in the incorrect trials. However, they only showed looks to the moved-element picture for the correct trials, parallel to control participants. Furthermore, aphasic individuals' fixations during movement sentences were just as fast as control participants' fixations. These results are unexpected under slowed-processing accounts of aphasic comprehension deficits, in which the source of failed comprehension should be delayed application of the same processing routines used in successful comprehension. This pattern is also unexpected if aphasic individuals are using qualitatively different strategies than normals to comprehend such sentences, as under impaired-representation accounts of agrammatism. Instead, it suggests that agrammatic aphasic individuals may process wh- questions similarly to unimpaired individuals, but that this process often fails to facilitate off-line comprehension of sentences with wh- movement.

Time-course of semantic composition: the case of aspectual coercion

We examine the time-course of semantic structure formation during real-time sentence comprehension. We do this through the lens of aspectual coercion, a semantic combinatorial operation that lacks morpho-syntactic reflections, yet is indispensable for sentence interpretation. We describe two experiments. Experiment 1 replicates the results of a previously published study (Piñango, Zurif, & Jackendoff, Journal of Psycholinguistic Research, 28(4), 395-414 1999) showing that the cost of implementing aspectual coercion is detectable as late as 250 ms after the operation is licensed. Experiment 2 expands the window of observation by revealing that the implementation of aspectual coercion is not detectable immediately upon its being licensed, that is, at the point at which the syntactic representation is assumed to be fully formed. These findings suggest a dissociation in the integration of information, in which semantic composition--even mandatory and automatic semantic composition-takes time to develop after it is syntactically licensed to do so.

Prosodic clues to syntactic processing—a PET and ERP study

Syntactic processing of spoken speech often involves prosodic clues processing. In the present PET and ERP study, subjects listened to phrases in which different prosodic segmentation dramatically changed the meaning of the phrase. In the contrast of segmented vs. non-segmented phrases, PET data revealed activation in the right dorsolateral prefrontal cortex and in the right cerebellum. These brain structures, therefore, might be part of the syntactic analysis network involved in prosodic segmentation and pitch processing. ERP results revealed frontal negativity that was sensitive to the position of the segmenting pause, possibly reflecting prosody-based semantic prediction. The present results are discussed in the context of their relation to brain networks of emotions, prosody, and syntax perception.

Interpretation of pronouns in VP-ellipsis constructions in Dutch Broca's and Wernicke's aphasia

In this paper, we investigate the ability of Dutch agrammatic Broca's and Wernicke's aphasics to assign reference to possessive pronouns in elided VP constructions. The assumption is that the comprehension problems in these two populations have different sources that are revealed in distinct patterns of responses. The focus is primarily on the performance of the agrammatic group whose errors in comprehension are not viewed as a consequence of a breakdown of grammatical knowledge but as a result of limited processing resources (for an overview see Grodzinsky, 2000). The results of the present study provide evidence for the psycholinguistic reality of the economy hierarchy as proposed in the Primitives of Binding (Reuland, 2001). According to the economy hierarchy proposed for the non-brain-damaged, the more economical semantic dependencies are preferred over the costlier discourse dependencies. This hierarchy is reflected in agrammatic aphasia where the semantic dependencies are available on time and preferred over the discourse dependences that are not available on time as a result of the lack of processing resources with consequences for comprehension.

Aphasic Deficits in Syntactic Processing

Two main classes of theories of deficits in syntactic processing in aphasia have been suggested: impairments affecting specific syntactic operations and reductions in resources available for syntactic processing. This paper reviews the data upon which such theories are based and argues that they may support only the latter type of model.

Central versus lateral presentation in hemispheric sentence processing: A paradoxical finding

There is considerable current interest in the question of the contribution of the right cerebral hemisphere to the comprehension of complex linguistic entities such as sentences and scripts. A problem in this field has been the difficulty of distinguishing between the consequences of lexical and message-level activation. The present study used a cross-modal lexical priming (CMLP) procedure to visually sample activation of word concepts at three different points during the auditory presentation of a sentence. Our aim was to contrast direct lexical activation following presentation of a word in the sentence with syntactic reactivation triggered by a subsequent anaphor. Visual word probes were presented to the right, left, and central visual fields, in order to permit hemispheric performance to be evaluated in relation to previous research confined to central presentations. The results were surprising. LVF probes revealed activation immediately following the target word, RVF probes exhibited activation three words downstream from the target, and centrally presented probes exhibited activation at all three sampling points. The most puzzling aspect of these results was the paradoxical finding that central presentations showed strong activation upon encountering an anaphor of the target, while neither lateral probe revealed any activation at all. We relate these results to recent research on the hemispheric implications of split-foveal word presentation, and suggest that simultaneous stimulation of the two hemispheres may be critical in evoking responses mediated by high-level integrative mechanisms requiring collaborative hemispheric processing.

Searching for the trace: the influence of age, lexical activation and working memory on sentence processing

To investigate the stability of trace reactivation in healthy older adults, 22 older volunteers with no significant neurological history participated in a cross-modal priming task. Whilst both object relative center embedded (ORC) and object relative right branching (ORR) sentences were employed, working memory load was reduced by limiting the number of words separating the antecedent from the gap for both sentence types. Analysis of the results did not reveal any significant trace reactivation for the ORC or ORR sentences. The results did reveal, however, a positive correlation between age and semantic priming at the pre-gap position and a negative correlation between age and semantic priming at the gap position for ORC sentences. In contrast, there was no correlation between age and priming effects for the ORR sentences. These results indicated that trace reactivation may be sensitive to a variety of age related factors, including lexical activation and working memory. The implications of these results for sentence processing in the older population are discussed.

Broca's Area and Inflectional Morphology: Evidence from Broca's Aphasia and Computer Modeling

In a series of articles Ullman (2001, 2004; Ullman et al., 1997) has proposed that regular inflection is critically subserved by Broca's area. This suggestion is motivated by the finding that English speaking Broca's aphasics show selective deficits with regular inflection. Here we argue that this proposal does not hold cross-linguistically but is based on a confound between inflectional suffix and regularity that is specific to the English language. We present data from two experimental studies of participle inflection with 13 German and 12 Dutch Broca's aphasics. None of these aphasic speakers are selectively impaired for regular inflection but instead most of them show selective deficits with irregular inflection. These data suggest that a selective regular deficit is not a characteristic of Broca's aphasia across languages, and that Broca's area is not critically involved in regular inflection. To investigate the nature and localization of the processes underlying inflection we present a connectionist neural network model that accounts for the deficits of the German aphasic speakers. The model implements the view that the inflection of all verb types is based on a single mechanism with multiple representations that emerge from experience-dependent brain development. We show that global damage to this model results in a selective deficit for irregular inflection that is comparable to that of the German aphasic speakers. This finding suggests that a selective impairment of irregular participles as observed by German and Dutch aphasic speakers does not presuppose two distinctly localized mechanisms or processes that can be selectively affected by brain damage.

Linguistic processing in visual and modality-nonspecific brain areas: PET recordings during selective attention

Positron emission tomography (PET) was used to investigate the neural basis of selective processing of linguistic material during concurrent presentation of multiple stimulus streams ("cocktail-party effect"). Fifteen healthy right-handed adult males were to attend to one of three simultaneously presented messages: one presented visually, one to the left ear, and one to the right ear. During the control condition, subjects attended to visually presented consonant letter strings and ignored auditory messages. This paper reports the modality-nonspecific language processing and visual word-form processing, whereas the auditory attention effects have been reported elsewhere [Cogn. Brain Res. 17 (2003) 201]. The left-hemisphere areas activated by both the selective processing of text and speech were as follows: the inferior prefrontal (Brodmann's area, BA 45, 47), anterior temporal (BA 38), posterior insular (BA 13), inferior (BA 20) and middle temporal (BA 21), occipital (BA 18/30) cortices, the caudate nucleus, and the amygdala. In addition, bilateral activations were observed in the medial occipito-temporal cortex and the cerebellum. Decreases of activation during both text and speech processing were found in the parietal (BA 7, 40), frontal (BA 6, 8, 44) and occipito-temporal (BA 37) regions of the right hemisphere. Furthermore, the present data suggest that the left occipito-temporal cortex (BA 18, 20, 37, 21) can be subdivided into three functionally distinct regions in the posterior-anterior direction on the basis of their activation during attentive processing of sublexical orthography, visual word form, and supramodal higher-level aspects of language.

Linguistic theory and neuroimaging evidence: an fMRI study of Broca's area in lexical semantics

There has been a long debate on the functional characterization of left inferior frontal cortex, including proposals regarding syntactic and lexico-semantic involvement. We studied nine right-handed adults, using functional magnetic resonance imaging (fMRI) during performance on a semantic decision task in which subjects had to determine whether noun-verb pairs were semantically associated. In comparison with a visuoperceptual control task, activation clusters were seen in left inferior frontal and middle temporal regions, as well as the bilateral superior frontal gyrus. In agreement with previous studies, our findings suggest that Broca's area is involved in semantic processing. Findings of lexico-semantic as well as syntactic processing in the inferior frontal lobe may be accounted for in terms of working memory demands.

Effects of age and speed of processing on rCBF correlates of syntactic processing in sentence comprehension

Positron emission tomography (PET) was used to determine the effect of age on regional cerebral blood flow (rCBF) during syntactic processing in sentence comprehension. PET activity associated with making plausibility judgments about syntactically more complex subject object (SO) sentences (e.g., The juice that the child spilled stained the rug) was compared to that associated with making judgments about synonymous syntactically simpler object subject (OS) sentences (e.g., The child spilled the juice that stained the rug). In the first study, 13 elderly (70-80-year-old) subjects showed increased rCBF in the left inferior parietal lobe. This result contrasted with previous studies, which have shown activation in Broca's area in this task in young subjects. Elderly subjects were noted to have longer reaction times than young subjects previously tested. A second study found that young subjects whose reaction times were as long as those of the elderly subjects tested in Experiment 1 activated left superior parietal, and not left inferior frontal, structures. A third experiment found that elderly subjects with reaction times as fast as previously tested young subjects activated left inferior frontal structures. The results suggest that the speed of syntactic processing, but not age per se is related to the neural location where one aspect of syntactic processing is carried out.

On-line syntactic processing in aphasia: studies with auditory moving window presentation

Twenty-eight aphasic patients with left hemisphere strokes and matched control subjects were tested on an auditory moving windows task in which successive phrases of a sentence were presented in response to subjects' self-paced button presses and subjects made timed judgments regarding the plausibility of each sentence. Pairs of sentences were presented that differed in syntactic complexity. Patients made more errors and/or took longer in making the plausibility judgments than controls, and were more affected than controls by the syntactic complexity of a sentence in these judgments. Normal subjects showed effects of syntactic structure in self-paced listening. On-line syntactic effects differed in patients as a function of their comprehension level. High-performing patients showed the same effects as normal control subjects; low performing patients did not show the same effects of syntactic structure. On-line syntactic effects also differed in patients as a function of their clinical diagnosis. Broca's aphasic patients' on-line performances suggested that they were not processing complex syntactic structures on-line, while fluent aphasics' performances suggested that their comprehension impairment occurred after on-line processing was accomplished. The results indicate that many aphasic patients retain their ability to process syntactic structure on-line, and that different groups of patients with syntactic comprehension disorders show different patterns of on-line syntactic processing.

Cognitive resources during sentence processing in Alzheimer's disease

This study assessed sentence comprehension in Alzheimer's disease (AD) while minimizing executive resource demands. AD patients (n=17) and healthy elderly control subjects (n=17) were asked to detect a word in a sentence. Unbeknownst to subjects, the target word at times followed an incorrect grammatical or semantic agreement. Control subjects took significantly longer to respond to a target word when it immediately followed an agreement violation compared to a coherent agreement, a difference that was not evident when the target word followed the agreement by several syllables. AD patients did not demonstrate a discrepancy between a violation and a coherent agreement in the immediate vicinity of the agreement, but demonstrated a significant delay in their response to a target word when it followed an agreement violation--particularly a violation of a grammatical agreement--by several syllables. Analyses of individual patient performance profiles revealed the pattern of delayed sensitivity to agreements in a majority of AD patients. Correlation and regression analyses associated AD patients' sensitivity to agreement violations over an abnormally delayed time course with a measure of inhibitory control, although weaker associations were also evident with measures of planning and short-term memory. We hypothesize that difficulty understanding grammatically complex sentences in AD is related to slowed information processing speed that restricts the timely construction of a sentence's structure and limits inhibition of canonical sentence interpretations such as first-noun-is-subject.

Vascular responses to syntactic processing: event-related fMRI study of relative clauses

Event-related functional magnetic resonance imaging was used to investigate the localization of syntactic processing in sentence comprehension. Matched pairs of sentences containing identical lexical items were compared. One member of the pair consisted of a syntactically simpler sentence, containing a subject relativized clause. The second member of the pair consisted of a syntactically more complex sentence, containing an object relativized clause. Ten subjects made plausibility judgments about the sentences, which were presented one word at a time on a computer screen. There was an increase in BOLD hemodynamic signal in response to the presentation of all sentences compared to fixation in both right and left occipital cortex, the left perisylvian cortex, and the left premotor and motor areas. BOLD signal increased in the left angular gyrus when subjects processed the complex portion of syntactically more complex sentences. This study shows that a hemodynamic response associated with processing the syntactically complex portions of a sentence can be localized to one part of the dominant perisylvian association cortex.

Language deficits, localization, and grammar: evidence for a distributive model of language breakdown in aphasic patients and neurologically intact individuals

Selective deficits in aphasic patients' grammatical production and comprehension are often cited as evidence that syntactic processing is modular and localizable in discrete areas of the brain (e.g., Y. Grodzinsky, 2000). The authors review a large body of experimental evidence suggesting that morpho-syntactic deficits can be observed in a number of aphasic and neurologically intact populations. They present new data showing that receptive agrammatism is found not only over a range of aphasic groups, but is also observed in neurologically intact individuals processing under stressful conditions. The authors suggest that these data are most compatible with a domain-general account of language, one that emphasizes the interaction of linguistic distributions with the properties of an associative processor working under normal or suboptimal conditions.

Syntax and the brain: disentangling grammar by selective anomalies

Many paradigms employed so far with functional imaging in language studies do not allow a clear differentiation of the semantic, morphological, and syntactic components, as traditionally defined within linguistic theory. In fact, many studies simply consider the brain's response to lists of unrelated words, rather than to syntactic structures, or do not neutralize the confounding effect of the semantic component. In the present PET experiment, we isolated the functional correlates of morphological and syntactic processing. The neutralization of the access to the lexical-semantic component was achieved by requiring the detection of anomalies in written sentences consisting of pseudowords. In both syntactic and morphosyntactic processing, the involvement of a selective deep component of Broca's area and of a right inferior frontal region was detected. In addition, within this system, the left caudate nucleus and insula were activated only during syntactic processing, indicating their role in syntactic computation. These findings provide original in vivo evidence that these brain structures, whose individual contribution has been highlighted by clinical studies, constitute a neural network selectively engaged in morphological and syntactic computation.

On processing lexical meanings in aphasia and Alzheimer's disease: some (re)considerations

The time course of lexical inferences during language comprehension is discussed according to a Lexical Inference Model (LIM). It distinguishes among three types of lexical inferences, respectively generated from semantic, conceptual, and strategic representations. Following discussion of the model, data from lexical priming studies conducted with aphasic patients as well as with Alzheimer's Disease patients are (re)considered in light of the LIM. The view that "word-level priming" (WLP) is not a sufficient task to tap in the time course of lexical activation during online processing is favored. Since most lexical priming studies on aphasia and Alzheimer's Disease used the WLP paradigm with an interstimulus interval larger than 100 ms, initial claims regarding automatic or modularized lexical processing are shown to be premature. However, the deficient lexical access or integration processes found in aphasias of the Broca and Wernicke types and in the dementia of the Alzheimer type are predicted by the LIM.

PET studies of syntactic processing with auditory sentence presentation

Sixteen subjects made plausibility judgments regarding auditorily presented cleft object and cleft subject sentences (It was the actress that the award thrilled; It was the award that thrilled the actress). rCBF increased in Broca's area, pars triangularis, when subjects processed the syntactically more complex cleft object sentences. The results are consistent with previous experiments using written materials and suggest that an increase in rCBF in Broca's area is associated with processing syntactically more complex sentences.

Auditory belt and parabelt projections to the prefrontal cortex in the rhesus monkey

Recent anatomical and electrophysiological studies have expanded our knowledge of the auditory cortical system in primates and have described its organization as a series of concentric circles with a central or primary auditory core, surrounded by a lateral and medial belt of secondary auditory cortex with a tertiary parabelt cortex just lateral to this belt. Because recent studies have shown that rostral and caudal belt and parabelt cortices have distinct patterns of connections and acoustic responsivity, we hypothesized that these divergent auditory regions might have distinct targets in the frontal lobe. We, therefore, placed discrete injections of wheat germ agglutinin-horseradish peroxidase or fluorescent retrograde tracers into the prefrontal cortex of macaque monkeys and analyzed the anterograde and retrograde labeling in the aforementioned auditory areas. Injections that included rostral and orbital prefrontal areas (10, 46 rostral, 12) labeled the rostral belt and parabelt most heavily, whereas injections including the caudal principal sulcus (area 46), periarcuate cortex (area 8a), and ventrolateral prefrontal cortex (area12vl) labeled the caudal belt and parabelt. Projections originating in the parabelt cortex were denser than those arising from the lateral or medial belt cortices in most cases. In addition, the anterior third of the superior temporal gyrus and the dorsal bank of the superior temporal sulcus were also labeled after prefrontal injections, confirming previous studies. The present topographical results suggest that acoustic information diverges into separate streams that target distinct rostral and caudal domains of the prefrontal cortex, which may serve different acoustic functions.

Effects of syntactic structure and propositional number on patterns of regional cerebral blood flow

Positron emission tomography (PET) was used to determine regional cerebral blood flow (rCBF) as a function of the syntactic form and propositional density of sentences. rCBF increased in the left pars opercularis, part of Broca's area, when subjects processed syntactically more complex sentences. There were no differences in rCBF in the perisylvian association cortex traditionally associated with language processing when subjects made plausibility judgments about sentences with two propositions as compared to sentences with one proposition, but rCBF increased in infero-posterior brain regions. These results suggest that there is a specialization of neural tissue in Broca's area for constructing aspects of the syntactic form of sentences to determine sentence meaning. They also suggest that this specialization is separate from the brain systems that are involved in utilizing the meaning of a sentence that has been understood to accomplish a task.

The neurology of empty categories aphasics' failure to detect ungrammaticality

A direct investigation into the grammatical abilities of Broca's and Wernicke's aphasics sought to obtain critical evidence for a revised model of the functional neuroanatomy of language. We examined aphasics' ability to make grammaticality judgments on a set of theoretically selected, highly complex syntactic structures that involve, most prominently, fine violations of constraints on syntactic movement. Although both groups have been thought to possess intact abilities in this domain, we discovered severe deficits; Broca's and Wernicke's aphasics (whose performances differed) exhibited clear, delineated, and grammatically characterizable deficits - they follow from the Trace-Deletion Hypothesis, which is motivated by independent comprehension results. These conclusions have both linguistic and neurological implications; Linguistically, they show that the aphasic deficit interacts with more than one module of the grammar. Namely, it manifests not only when the thematic module is called for in interpretive tasks but also when constraints on syntactic movement are tapped in a study of judgment. Neurologically, the results support a view of receptive grammatical mechanisms in the left cortex, which is functionally more restrictive than currently assumed; neuroanatomically, however, it is more distributed.

Gap-filling and end-of-sentence effects in real-time language processing: implications for modeling sentence comprehension in aphasia

We present an on-line study showing different sources of lexical activation during sentence comprehension, distinguishing in this respect between reflexive syntactic and less temporarily constrained nonsyntactic sources. Specifically, we show that both the syntactic process of gap filling and a nonsyntactic end-of-sentence effect can be measurable in real time and can be temporally separated. The distinction between activation sources provides a new perspective on real-time sentence comprehension in aphasia and accounts for the disparate results reported in the literature.

Tutorial: an introduction to syntax

This paper is intended as an introduction to syntax. Borrowing from Chomsky's Government & Binding and Principles & Parameters frameworks (Chomsky, 1986, 1992, 1995), various aspects of syntactic theory are described. These include lexical, functional, and phrasal categories and how they are put together into clauses and sentences, how words are represented in the mental lexicon, how lexical properties project to the syntax, and how noun phrases are assigned structural and semantic information. Additionally, how sentences that are not canonically ordered are derived and represented, how and to what do pronouns refer, and the principles that connect all these theoretical notions to form knowledge of language are described. The paper concludes with a summary of work in normal and disordered language, including treatment of language disorders, that has exploited aspects of the syntactic theory described in this paper.

Training and generalized production of wh- and NP-movement structures in agrammatic aphasia

The present research examines production of "complex" sentences, which involve movement of noun phrases (NPs), in 2 agrammatic aphasic subjects. According to linguistic theory (Chomsky, 1991, 1993), such sentences are derived using one of two movement operations, either wh- or NP-movement, subsumed under the general rule "move alpha." In this experiment recovery of both wh- and NP-movement derived sentences was investigated using a treatment research paradigm. Subjects were sequentially trained to produce either wh-movement (i.e., who questions, object clefts) or NP-movement (i.e., passives, subject-raising structures) derived sentences. Throughout training, generalization to untrained sentences relying on both types of movement was tested. The influence of training on aspects of narrative discourse also was examined. Results showed generalization patterns constrained to type of movement. Training wh-movement structures resulted in generalized production of untrained wh-movement structures without influencing production of NP-movement structures. Similarly, training of NP-movement structures resulted in generalization only to other sentence types also relying on NP-movement. Aspects of sentence production in narrative contexts also was improved with treatment. These data indicate that movement to an argument (A) position as in NP-movement is distinct from movement to a non-argument (A-bar) position, required in wh-movement. The site where movement terminates in the s-structure of noncanonical sentences appears to influence sentence production. These findings show that linguistic properties of sentences influence sentence production breakdown and recovery in aphasia.

Grammatical theory and the study of sentence comprehension in aphasia: comments on Druks and Marshall (1995)

Druks and Marshall (1995) argue that aphasic comprehension problems are accountable as the consequence of a disrupted Case assignment module. But the analysis they present does not support their argument and it provides a distorted view of grammatically based analyses of brain-language relations.

Coreference processing and levels of analysis in object-relative constructions; demonstration of antecedent reactivation with the cross-modal priming paradigm

This paper is concerned with two related issues in sentence processing--one methodological and one theoretical. Methodologically, it provides an unconfounded test of the ability of the cross-modal lexical priming task, when used appropriately, to provide detailed evidence about the time-course of antecedent reactivation during sentence processing. Theoretically, it provides a study of the nature of the representation that is examined when a reference-seeking element is linked to its antecedent during the processing of object-relative clause constructions. In these studies, subjects heard sentences which contained a lexical ambiguity placed in a strong biasing context. In one study this ambiguous word was the "moved" or "fronted" object of the verb in an object-relative construction. A cross-modal lexical priming (CMLP) naming task was used to determine whether one or more of the meanings of the ambiguity are activated at three temporally distinct points during the sentence: (1) immediately after the lexical ambiguity (Study 1); (2) a later point that was 700 milliseconds before the offset of the main verb (Study 2); (3) immediately after this main verb (at the gap in this filler-gap construction) (Study 2). The probes in the CMLP task were controlled for potential confounds. The results demonstrate the following: At Test Point 1, all meanings of the ambiguity were activated; at Test Point 2, neither meaning of the ambiguity was (still) activated; at Test Point 3, only a single (context-relevant) meaning of the ambiguity was reactivated. It is concluded that an underlying (deep; non-surface-level) memorial representation of the sentence is examined during the process of linking an antecedent to a structural position requiring a referent, and that the CMLP task provides an unbiased measure of this reactivation. Further, it is concluded that this effect cannot be accounted for under a "compound cue" (Ratcliff & McKoon, 1994) explanation.