Semantic and syntactic processes during sentence comprehension in patients with schizophrenia: evidence from event-related potentials

Linguistic anomalies observed in the Sentence Completion Test in patients with schizophrenia

BACKGROUND

Schizophrenia is a chronic, debilitating disorder characterised by distorted thinking, perceptions, behaviours, and even language impairments. We investigated the linguistic anomalies in Korean schizophrenia patients compared to non-psychotic psychiatric controls to determine whether the linguistic anomalies in English speakers with schizophrenia were replicated in Korean speakers.

METHODS

Thirty-four schizophrenia patients and 70 non-psychotic psychiatric controls were included in this study. The SCT was utilised as the text data for analysis. For linguistic analysis, we evaluated texts regarding semantics and syntax. We separately counted the number of semantic or syntactic errors in the written texts of study participants and compared them between patients and controls.

RESULTS

Schizophrenia patients showed significantly more semantic errors (p < .001) and syntactic errors (p < .001) per 1,000 characters than non-psychotic psychiatric controls. Specifically, inappropriate word or syntactic component selection is noticeable in schizophrenia patients. These differences were still significant after adjusting for general intelligence measured by the K-WAIS-IV.

CONCLUSION

Schizophrenia patients showed both semantic and syntactic errors in written language. Moreover, these errors seemed to be partly independent of general intelligence. Notably, patients showed a noticeable number of syntactic errors. Further investigation into the language of patients with schizophrenia and schizophrenia-spectrum disorders is required.

Agency of Subjects and Eye Movements in Schizophrenia Spectrum Disorders

People with schizophrenia spectrum disorders (SSD) show anomalies in language processing with respect to "who is doing what" in an action. This linguistic behavior is suggestive of an atypical representation of the formal concepts of "Agent" in the lexical representation of a verb, i.e., its thematic grid. To test this hypothesis, we administered a silent-reading task with sentences including a semantic violation of the animacy trait of the grammatical subject to 30 people with SSD and 30 healthy control participants (HCs). When the anomalous grammatical subject was the Agent of the event, a significant increase of Gaze Duration was observed in HCs, but not in SSDs. Conversely, when the anomalous subject was a Theme, SSDs displayed an increased probability of go-back movements, unlike HCs. These results are suggestive of a higher tolerability for anomalous Agents in SSD compared to the normal population. The fact that SSD participants did not show a similar tolerability for anomalous Themes rules out the issue of an attention deficit. We suggest that general communication abilities in SSD might benefit from explicit training on deep linguistic structures.

Evaluation of N-400 Evoked Response Potential in schizophrenia: An endophenotype or a disease marker?

N400 evoked response potentials (ERP) reliably map key semantic deficits in schizophrenia. Assessing them as endophenotypes might help in better understanding of schizophrenia risk and their use as biomarkers. We aimed to study N400 as an endophenotype marker by comparing schizophrenia (SCZ), unaffected first-degree relatives (FDR) and healthy controls (HC) and, by assessing its ability to discriminate these groups. Drug naïve or free SCZ probands (n=30), their unaffected FDRs (n=30) and HC (n=30), underwent a 40-channel ERP recording while performing a custom-made, Hindi- sentence context paradigm task, containing congruent and incongruent conditions. Fifteen centro-parietal (CP) leads, further classified into three regions-midline (CPM), right (CPR) and left (CPL) were selected as electrodes-of-interest for assessing N400. During the incongruent condition, compared to both FDRs and HC, SCZ showed significantly longer N400 latency, at CPM, CPR and CPL, and significantly lesser (more negative) amplitude, at CPM; no significant difference was noted between FDR and HC groups. On discriminant functional analysis, significant N400 predictors could accurately classify 73.3% SCZ from HC and 75% of SCZ from FDR. We conclude that N400 deficits, elicited by the incongruent condition of the sentence task, could be potential biomarkers to define disease state in schizophrenia; they may not be endophenotype markers.

Language-Related Neurophysiological Deficits in Schizophrenia

Schizophrenia is a severe psychiatric disorder that affects all aspects of one's life with several cognitive and social dysfunctions. However, there is still no objective and universal index for diagnosis and treatment of this disease. Many researchers have studied language processing in schizophrenia since most of the patients show symptoms related to language processing, such as thought disorder, auditory verbal hallucinations, or delusions. Electroencephalography (EEG) and magnetoencephalography (MEG) with millisecond order high temporal resolution, have been applied to reveal the abnormalities in language processing in schizophrenia. The aims of this review are (a) to provide an overview of recent findings in language processing in schizophrenia with EEG and MEG using neurophysiological indices, providing insights into underlying language related pathophysiological deficits in this disease and (b) to emphasize the advantage of EEG and MEG in research on language processing in schizophrenia.

Reading deficits in schizophrenia and their relationship to developmental dyslexia: A review

Although schizophrenia and developmental dyslexia are considered distinct disorders in terms of clinical presentation and functional outcome, they both involve disruption in the processes that support skilled reading, including language, auditory perception, visual perception, oculomotor control, and executive function. Further, recent work has proposed a common neurodevelopmental basis for the two disorders, as suggested by genetic and pathophysiological overlap. Thus, these lines of research suggest that reading may be similarly impacted in schizophrenia and dyslexia. In this review, we survey research on reading abilities in individuals with schizophrenia, and review the potential mechanisms underlying reading deficits in schizophrenia that may be shared with those implicated in dyslexia. Elucidating the relationship between reading impairment in schizophrenia and dyslexia could allow for a better understanding of the pathophysiological underpinnings of schizophrenia, and could facilitate remediation of cognitive deficits that impact day-to-day functioning.

P600 alteration of syntactic language processing in patients with bipolar mania: Comparison to schizophrenic patients and healthy subjects

BACKGROUND

Disturbances in thought, speech, and linguistic processing are frequently observed in bipolar manic patients, but the underlying neurophysiological mechanisms are not well understood. P600 is a distinct, positive event-related potential component elicited by syntactic violations. Using the P600 ERP, we examined neural processing of syntactic language comprehension in patients with bipolar mania compared to patients with schizophrenia and healthy people.

METHOD

P600s were recorded from 21 manic patients with bipolar disorder, 26 patients with schizophrenia, and 29 healthy subjects during the presentation of 120 auditory sentences with syntactic violations or non-violations. Subjects were asked to judge whether each sentence was correct or incorrect.

RESULTS

Patients with mania and schizophrenia had significantly smaller P600 amplitudes associated with syntactic violations compared with healthy subjects. There was no difference in P600 amplitude between patient groups. For behavioral performance, patients with schizophrenia had significantly less accurate rates and longer reaction times compared with healthy subjects, whereas manic patients exhibited no significant differences in accuracy and only showed increased reaction times in comparison with healthy subjects.

LIMITATIONS

Psychotropic drug usage and small sample size.

CONCLUSION

Patients with bipolar mania have reduced P600 amplitude, comparable to patients with schizophrenia. Our findings may represent the first neurophysiological evidence of abnormal syntactic linguistic processing in bipolar mania.

Haemodynamic and electrophysiological markers of pragmatic language comprehension in schizophrenia

OBJECTIVES

The present study aimed at investigating neurophysiological markers of language perception in schizophrenia using simultaneous near-infrared spectroscopy (NIRS) and event-related potentials (ERPs), which have been proven to be useful for studying language processing abilities in psychiatric patients. The study shall help to integrate previous findings from ERP and fMRI studies on figurative language comprehension in schizophrenia and elucidate how electrophysiological and haemodynamic markers of language processing are related.

METHODS

Twenty-two healthy subjects and 22 schizophrenia patients judged 120 sentences regarding their meaningfulness. Phrases were literal, metaphoric, or meaningless. EEG-fNIRS signals were recorded throughout the entire experiment.

RESULTS

Schizophrenia patients showed deficient and delayed sentence comprehension. Both the early N400 and left-hemispheric activation during language comprehension were altered in patients. Correlation analyses showed that metaphor-related ERPs were strongly linked to haemodynamic cortical activity in healthy subjects, but not in patients.

CONCLUSIONS

Our results indicate group differences in cortical electrophysiological and haemodynamic activation that represent rather general impairments in the processing of complex language. Simultaneous EEG/NIRS applications are useful to depict these neural markers and to investigate their relationship. Future studies are needed to clarify the nature of respective anomalies and their potential as putative neural markers in schizophrenia research.

Localization of electrophysiological responses to semantic and syntactic anomalies in language comprehension with MEG

Syntactically and semantically anomalous words encountered during sentence comprehension are known to elicit dissociable electrophysiological responses, which are thought to reflect distinct aspects of language processing. However, the sources of these responses have not been well characterized. We used beamforming analysis of magnetoencephalography (MEG) data to map generators of electrophysiological responses to linguistic anomalies. Anomalous words occurred in the context of a sentence acceptability judgement task conducted in both visual and auditory modalities. Time-frequency analysis revealed that both kinds of violations elicited event-related synchronization (ERS) in the delta-theta frequency range (1-5 Hz), and desynchronization (ERD) in the alpha-beta range (8-30 Hz). In addition, these responses were differentially modulated by violation type and presentation modality. 1-5 Hz responses were consistently localized within medial prefrontal cortex and did not vary significantly across violation types, but were stronger for visual presentation. In contrast, 8-30 Hz ERD occurred in different regions for different violation types. For semantic violations the distribution was predominantly in the bilateral occipital cortex and left temporal and inferior frontal regions, and these effects did not differ for visual and auditory presentation. In contrast, syntactic responses were strongly affected by presentation modality. Under visual presentation, syntactic violations elicited bilateral 8-30 Hz ERD extending into dorsal parietal and frontal regions, whereas effects were much weaker and mostly statistically insignificant in the auditory modality. These results suggest that delta-theta ERS reflects generalized increases in working memory demands related to linguistic anomaly detection, while alpha-beta ERD reflects specific activation of cortical regions involved in distinct aspects of linguistic processing, such as semantic vs. phonological short-term memory. Beamforming analysis of time-domain average signals (ERFs) revealed an N400m effect for semantic anomalies in both modalities, localized to left superior temporal and posterior frontal regions, and a later P600-like effect for syntactic anomalies in both modalities, widespread over bilateral frontal, posterior temporal, and parietal regions. These results indicate that time-domain averaged responses and induced oscillatory responses have distinct properties, including localization and modality dependence, and likely reflect dissociable and complementary aspects of neural activity related to language comprehension and additional task-related processes.

Natural speech comprehension in bipolar disorders: an event-related brain potential study among manic patients

BACKGROUND

Thought and language disturbances are crucial clinical features in Bipolar Disorders (BD), and constitute a fundamental basis for social cognition. In BD, clinical manifestations such as disorganization and formal thought disorders may play a role in communication disturbances. However, only few studies have explored language disturbances in BD at a neurophysiological level. Two main Event-Related brain Potentials (ERPs) have been used in language comprehension research: the N400 component, elicited by incongruous word with the preceding semantic context, and the Late Positive Component (LPC), associated with non-specifically semantic and more general cognitive processes. Previous studies provided contradictory results regarding N400 in mood disorders, showing either preserved N400 in depression or dysthymia, or altered N400 in BD during semantic priming paradigm. The aim of our study was to explore N400 and LPC among patients with BD in natural speech conditions.

METHODS

ERPs from 19 bipolar type I patients with manic or hypomanic symptomatology and 19 healthy controls were recorded. Participants were asked to listen to congruous and incongruous complete sentences and to judge the match between the final word and the sentence context. Behavioral results and ERPs data were analyzed.

RESULTS

At the behavioral level, patients with BD show worst performances than healthy participants. At the electrophysiological level, our results show preserved N400 component in BD. LPC elicited under natural speech conditions shows preserved amplitude but delayed latency in difference waves.

LIMITATIONS

Small size of samples, absence of schizophrenic group and medication status.

CONCLUSIONS

In contrast with the only previous N400 study in BD that uses written semantic priming, our results show a preserved N400 component in ecological and natural speech conditions among patients with BD. Possible implications in terms of clinical specificity are discussed.

N400 in schizophrenia patients

PURPOSE OF REVIEW

The purpose of this article is to review major findings in event related potential (ERP) research in schizophrenia patients, specifically focusing on the N400 component.

RECENT FINDINGS

Patients with chronic schizophrenia have difficulty using 'context' (understanding the meaning of the word relative to the sentence) in sentence processing studies and often show differences from control populations in language experiments using word priming. Both of these observations are associated with an abnormal N400 ERP component when compared with nonpsychotic individuals. Many studies of language function rely on priming paradigms that use pairs of words such that the first word in a pair is a 'prime' and a second word in a pair is a 'target', separated from the prime by a period of time known as the Stimulus Onset Asynchrony (SOA). If the SOA is short (i.e., below 400 ms) then it is believed that a priming study examines primarily processes of initial activation within semantic networks; if it is long (i.e., more than 400 ms) then it is believed that a priming study examines primarily processes of context use, generating predictions and matching these predictions against upcoming semantic information. Priming paradigms that use long SOAs are consistently associated with a more negative N400 (hence lack of priming) in schizophrenia, whereas priming paradigms using a short SOA produce either a normal N400 priming response or hyperpriming as shown by a reduced N400 and related to a hypothesized too rapid automatic spread of activation within the semantic memory pathway. Apparent differences among reported study results are likely due to paradigm differences that tap into different aspects of language processing. Although the presence of both hyperactivation within semantic networks and difficulties with the use of context is well known in schizophrenia, it is unclear whether these abnormalities are also present prior to illness onset in people who are at risk for development of schizophrenia or even present at the onset of illness.

SUMMARY

In order to clarify the findings reviewed here, future studies will be needed that focus on examining the N400 response in young people at high risk for developing the illness using multiple paradigms that probe different aspects of language function.

Linguistic production and syntactic comprehension in schizophrenia and bipolar disorder

OBJECTIVE

To explore linguistic abilities in schizophrenia and bipolar disorder. Specifically, the aims of this study were to: i) investigate microlinguistic (lexicon, morphology, syntax) and macrolinguistic (discourse coherence, pragmatics) dimensions of speech production and ii) evaluate syntactic comprehension skills in both schizophrenia and bipolar disorder.

METHOD

Linguistic performance of 30 Italian-speaking patients with schizophrenia, 30 participants with bipolar disorder and 30 healthy controls comparable for age and educational level has been assessed using a story-telling task and a computer-based test of syntactic comprehension.

RESULTS

In narrative production, compared with healthy participants, those with schizophrenia had slight problems in speech rate and deficits at both local and global discourse coherence, whereas patients with bipolar disorder showed reduced mean length of utterance. As regards syntactic comprehension, both groups of patients collected more grammatical errors than controls, but they differed with regard to the number and kind of grammatical construction they missed.

CONCLUSION

Linguistic deficits have been detected in both groups of patients, being, however, more severe and generalized in schizophrenia than in bipolar disorder. Such results help us in improving our understanding of the potential psychopathological overlapping between these disorders.

Impaired reading comprehension in schizophrenia: evidence for underlying phonological processing deficits

The present study examined reading ability in high functioning people with schizophrenia. To this end, 16 people with schizophrenia who were living in the community and 12 matched controls completed tests of passage reading (comprehension, accuracy, and rate), word recognition, and phonological processing (phonological awareness, phonological memory and rapid naming) and ratings of reading self-concept and practices. Performance of the participants with schizophrenia was impaired relative to control participants on reading comprehension and rapid naming and relative to the population norms on phonological awareness, and rapid naming. In addition, self-rating data revealed that participants with schizophrenia had poorer perceptions of their reading ability and engaged in reading activities less frequently than their control counterparts. Consistent with earlier research, significant correlations were found between phonological awareness and reading comprehension. These findings expand on previous research in the area to suggest that community-based individuals with schizophrenia experience problems with reading comprehension that may have a phonological basis.

Reduced P300 and P600 amplitude in the hollow-mask illusion in patients with schizophrenia

Illusions provide a useful tool to study the mechanisms by which top-down and bottom-up processes interact in perception. Patients suffering from schizophrenia are not as subject to the hollow-mask illusion as healthy controls, since studies have shown that controls perceive a hollow mask as a normal face, while patients with schizophrenia do not. This insusceptibility to the illusion is indicating a weakened top-down processing in schizophrenia and little is understood about the neurobiology of this phenomenon. We used event-related potentials to investigate the hollow-mask illusion in patients with schizophrenia and healthy controls. We hypothesized that there would be a visible reduction of top-down processing in the patients' group and that this reduction would occur in the late stages of processing. We found significantly decreased amplitudes in the P300 and P600 components in the patients' group, indicating that visual information does not benefit from frontal, parietal or temporal activity for perceiving incoming stimuli. We propose that a deficit in functional connectivity may be responsible for impaired top-down visual processing in schizophrenia. These data further the understanding of the time course of top-down processing in patients with schizophrenia.

Selective emotional processing deficits to social vignettes in schizophrenia: an ERP study

Schizophrenia is associated with abnormalities in emotional processing and social cognition. However, it remains unclear whether patients show abnormal neurophysiological responses during fast, online appraisals of the emotional meaning of social information. To examine this question, event-related potentials (ERPs) were collected while 18 schizophrenia patients and 18 demographically matched controls evaluated 2-sentence vignettes describing negative, positive, or neutral social situations. ERPs were time locked to a critical word (CW) in the second sentence that conferred emotional valence. A late positivity effect to emotional (vs neutral) CWs was seen in both groups (in controls, to negative and positive CWs; in patients, to negative CWs only). However, the controls showed a greater late positivity effect to the negative and positive (vs neutral) CWs than the schizophrenia patients at mid-posterior (negative vs neutral) and at right posterior peripheral (positive vs neutral) sites. These between-group differences arose from reduced amplitudes of the late positivity to the negative and positive CWs in the patients relative to the controls; there was no difference between the 2 groups in the amplitude of the late positivity to the neutral CWs. These findings suggest that schizophrenia is associated with a specific neural deficit during the online evaluation of emotionally valent, socially relevant information.

Language in schizophrenia Part 2: What can psycholinguistics bring to the study of schizophrenia...and vice versa?

This is the second of two articles that discuss higher-order language and semantic processing in schizophrenia. The companion article (Part 1) gives an introduction to language dysfunction in schizophrenia patients. This article reviews a selection of psycholinguistic studies which suggest that sentence-level abnormalities in schizophrenia may stem from a relative overdependence on semantic associative relationships at the expense of building higher-order meaning. Language disturbances in schizophrenia may be best conceptualized as arising from an imbalance of activity across two streams of processing, one drawing upon semantic relationships within semantic memory and the other involving the use of combinatorial mechanisms to build propositional meaning. I will also discuss some of the ways in which the study of schizophrenia may offer new insights into the cognitive and neural architecture of the normal language system.

What can Event-related Potentials tell us about language, and perhaps even thought, in schizophrenia?

Disturbances of thought and language are fundamental to schizophrenia. Cognitive behavioral and electrophysiological research has implicated problems in two different neurocognitive mechanisms: abnormalities in the structure and function of semantic memory, and abnormalities in combining and integrating words together to build up sentence and discourse context. This review discusses recent electrophysiological evidence suggesting that these two deficits are not completely distinct, but rather that language impairment in schizophrenia results from a dysfunctional interaction between these systems in an effort to build up higher-order meaning. Moreover, although language abnormalities are more pronounced in patients with positive thought disorder, they manifest themselves in all patients when increased demands are placed on the comprehension system. Further investigation of language dysfunction may also provide insights into other aspects of psychotic thought.

Neurocognitive mechanisms of conceptual processing in healthy adults and patients with schizophrenia

This overview outlines findings of cognitive and neurocognitive studies on comprehension of verbal, pictorial, and video stimuli in healthy participants and patients with schizophrenia. We present evidence for a distinction between two complementary neurocognitive streams of conceptual analysis during comprehension. In familiar situations, adequate understanding of events may be achieved by mapping the perceived information on the associative and similarity-based connections between concepts in semantic memory - a process reflected by an N400 waveform of event-related electrophysiological potentials (ERPs). However, in less conventional contexts, a more flexible mechanism may be needed. We suggest that this alternative processing stream, reflected by a P600 ERP waveform, may use discrete, rule-like goal-related requirements of real-world actions to comprehend relationships between perceived people, objects, and actions. This neurocognitive model of comprehension is used as a basis in discussing studies in schizophrenia. These studies suggest an imbalanced engagement of the two conceptual streams in schizophrenia, whereby patients may rely on the associative and similarity-based networks in semantic memory even when it would be more adaptive to recruit mechanisms that draw upon goal-related requirements. Finally, we consider the roles that these conceptual mechanisms may play in real-life behavior, and the consequences that their dysfunction may have for disorganized behavior and inability to plan actions to achieve behavioral goals in schizophrenia.

Neurocognitive abnormalities during comprehension of real-world goal-directed behaviors in schizophrenia

Origins of impaired adaptive functioning in schizophrenia remain poorly understood. Behavioral disorganization may arise from an abnormal reliance on common combinations between concepts stored in semantic memory. Avolition-apathy may be related to deficits in using goal-related requirements to flexibly plan behavior. The authors recorded event-related potentials (ERPs) in 16 patients with medicated schizophrenia and 16 healthy controls in a novel video paradigm presenting congruous or incongruous objects in real-world activities. All incongruous objects were contextually inappropriate, but the incongruous scenes varied in comprehensibility. Psychopathology was assessed with the Scales for the Assessment of Positive and Negative Symptoms (SAPS/SANS) and the Brief Psychiatric Rating Scale. In patients, an N400 ERP, thought to index activity in semantic memory, was abnormally enhanced to less comprehensible incongruous scenes, and larger N400 priming was associated with disorganization severity. A P600 ERP, which may index flexible object-action integration based on goal-related requirements, was abnormally attenuated in patients, and its smaller magnitude was associated with the SANS rating of impersistence at work or school (goal-directed behavior). Thus, distinct neurocognitive abnormalities may underlie disorganization and goal-directed behavior deficits in schizophrenia.

Functional magnetic resonance imaging reveals neuroanatomical dissociations during semantic integration in schizophrenia

BACKGROUND

Schizophrenia symptoms can be conceptualized in terms of a breakdown of a balance between 1) activating, retrieving, and matching stored representations to incoming information (semantic memory-based processing) and 2) fully integrating activated semantic representations with one another and with other types of representations to form a gestalt representation of meaning (semantic integration). Semantic memory-based processes are relatively more dependent on inferior frontal and temporal cortices, whereas particularly demanding integrative processes additionally recruit the dorsolateral prefrontal cortex (DLPFC) and sometimes parietal cortices. We used functional magnetic resonance imaging (fMRI) to determine whether the modulation of temporal/inferior frontal cortices and the DLPFC can be neuroanatomically dissociated in schizophrenia, as semantic integration demands increase. Integration demands were manipulated by varying the nature (concrete vs. abstract) and the congruity (incongruous vs. congruous) of words within sentences.

METHODS

Sixteen right-handed schizophrenia patients and 16 healthy volunteers, matched on age and parental socioeconomic status, underwent event-related fMRI scanning while they read sentences. Blood oxygen level dependent (BOLD) effects were contrasted to words within sentences that were 1) concrete versus abstract and 2) semantically incongruous versus congruous with their preceding contexts.

RESULTS

In both contrasts, large networks mediating the activation and retrieval of verbal and imagistic representations were normally modulated in patients. However, unlike control subjects, patients failed to recruit the DLPFC, medial frontal and parietal cortices to incongruous (relative to congruous) sentences, and failed to recruit the DLPFC to concrete (relative to abstract) sentences.

CONCLUSIONS

As meaning is built from language, schizophrenia patients demonstrate a neuroanatomical dissociation in the modulation of temporal/inferior frontal cortices and the DLPFC.

Clinical and neuropsychological correlates of white matter abnormalities in recent onset schizophrenia

The objective of this study was to investigate the clinical and neuropsychological correlates of white matter abnormalities in patients with schizophrenia studied early in the course of illness. A total of 33 (21 male/12 female) patients with recent onset schizophrenia and 30 (18 male/12 female) healthy volunteers completed structural and diffusion tensor imaging exams. Patients also received clinical and neuropsychological assessments. Fractional anisotropy (FA) maps were compared between groups in the white matter using a voxelwise analysis following intersubject registration to Talairach space and correlated with functional indices. Compared to healthy volunteers, patients demonstrated significantly (p<0.001, cluster size >or=100) lower FA within temporal lobe white matter regions corresponding approximately to the right and left uncinate fasciculus, left inferior fronto-occipital fasciculus, and left superior longitudinal fasciculus. There were no areas of significantly higher FA in patients compared to healthy volunteers. Lower FA in the bilateral uncinate fasciculus correlated significantly with greater severity of negative symptoms (alogia and affective flattening), and worse verbal learning/memory functioning. In addition, higher FA in the inferior fronto-occipital fasciculus correlated significantly with greater severity of delusions and hallucinations. White matter abnormalities are evident in patients with schizophrenia early in the course of illness, appearing most robust in left temporal regions. These abnormalities have clinical and neuropsychological correlates, which may be useful in further characterizing structure-function relations in schizophrenia and constraining neurobiological models of the disorder.

Electrophysiological Evidence for a Syntactic but Not a Semantic Deficit in Patients with Major Depression

Cognitive deficits are common in patients with major depression. The present study investigated whether these impairments also comprise language processes such as sentence comprehension. We studied four language-related evoked potentials (early left anterior negativity [ELAN], N400, left anterior negativity [LAN], and P600) in 14 patients with major depressive disorder (MDD) in partial remission and 14 matched healthy controls using a sentence paradigm with correct, semantic mismatching, and syntactic mismatching sentences. In contrast to controls, patients showed no significant P600 effect when comparing syntactic mismatching and correct sentences. No group differences could be observed for the ELAN, N400, and LAN components. The missing P600 effect may indicate deficits in the cognitive domain of language processing in depressive patients or impairment of a more general process to detect deviances from regularities. How this result integrates into the concept of a general cognitive deficit in major depression remains a goal for future studies.

Impaired multisensory processing in schizophrenia: deficits in the visual enhancement of speech comprehension under noisy environmental conditions

BACKGROUND

Viewing a speaker's articulatory movements substantially improves a listener's ability to understand spoken words, especially under noisy environmental conditions. In this study we investigated the ability of patients with schizophrenia to integrate visual and auditory speech. Our objective was to determine to what extent they experience benefit from visual articulation and to detail under what listening conditions they might show the greatest impairments.

METHODS

We assessed the ability to recognize auditory and audiovisual speech in different levels of noise in 18 patients with schizophrenia and compared their performance with that of 18 healthy volunteers. We used a large set of monosyllabic words as our stimuli in order to more closely approximate performance in everyday situations.

RESULTS

Patients with schizophrenia showed deficits in their ability to derive benefit from visual articulatory motion. This impairment was most pronounced at signal-to-noise levels where multisensory gain is known to be maximal in healthy control subjects. A surprising finding was that despite known early auditory sensory processing deficits and reports of impairments in speech processing in schizophrenia, patients' performance in unisensory auditory speech perception remained fully intact.

CONCLUSIONS

Thus, the results showed a specific deficit in multisensory speech processing in the absence of any measurable deficit in unisensory speech processing and suggest that sensory integration dysfunction may be an important and, to date, rather overlooked aspect of schizophrenia.

It's Early: Event-related Potential Evidence for Initial Interaction of Syntax and Prosody in Speech Comprehension

Psycholinguistic theories assume an interaction between prosody and syntax during language processing. Based on studies using mostly off-line methods, it is unclear whether an interaction occurs at later or initial processing stages. Using event-related potentials, the present study provides neurophysiological evidence for a prosody and syntax interaction in initial processing. The sentence material contained mere prosodic and syntactic as well as combined prosodic-syntactic violations. For the syntax violation, the critical word appeared after a preposition. The suffix of the critical word either indicated a noun fulfilling the syntactic requirements of the preceding preposition or a verb causing a word category violation. For the prosodic manipulation, congruent critical words were normally intonated (signaling sentence continuation) while prosodically incongruent critical words signaled sentence end. For the mere prosodic incongruity, a broadly distributed negativity was observed at the critical word-stem (300–500 msec aligned to word onset). In response to a mere syntactic error, a left temporal negativity was elicited in an early time window (200–400 msec aligned to suffix onset), taken to reflect initial phrase structure building processes. In contrast, in response to the combined prosodic-syntactic violation, an early temporal negativity showed up bilaterally at the suffix in the same time window. Our interpretation is that the process of initial structure building as reflected in the early left anterior negativity recruits additional right hemispheric neural resources when the critical word contains both syntactic and prosodic violations. This suggests the immediate influence of phrasal prosody during the initial parsing stage in speech processing.

Making sense of sentences in schizophrenia: Electrophysiological evidence for abnormal interactions between semantic and syntactic processing

Event-related potentials to critical verbs were measured as patients with schizophrenia and healthy controls read sentences word by word. Relative to their preceding context, critical verbs were (a) congruous, (b) incongruous and semantically unrelated to individual preceding words (pragmatic-semantic violations), (c) incongruous but semantically related to individual preceding words (animacy-semantic violations), or (d) syntactically anomalous. The N400 was modulated normally in patients, suggesting that semantic integration between individual words within sentences was normal in schizophrenia. The amplitude of the P600 to both syntactic and animacy-semantic violations was reduced in patients relative to controls. The authors suggest that, in schizophrenia, an abnormality in combining semantic and syntactic information online to build up propositional meaning leaves sentence processing to be primarily driven by semantic relationships between individual words.

ERPs of metaphoric, literal, and incongruous semantic processing in schizophrenia

The ability of schizophrenia patients to access metaphorical meaning was studied on the basis of psycholinguistic models of metaphor processing. ERPs were recorded from 20 schizophrenic and 20 control participants who were asked to read metaphorical, literal, and incongruous sentences and to judge their meaningfulness. In all participants, incongruous endings to sentences evoked the most negative N400 amplitude, whereas literal endings evoked more negative N400 amplitude than metaphorical ones, consistent with the direct model of metaphor processing. Although the patients had ERPs patterns that were similar to controls, they exhibited a more negative N400 amplitude for all sentences, LPC amplitude reduction, and latency delay in both components. The results suggest that schizophrenics have no specific anomalies in accessing the meaning of metaphors but are less efficient in integrating the semantic context of all sentences--both figurative and literal.

Late interaction of syntactic and prosodic processes in sentence comprehension as revealed by ERPs

The present study was designed to examine the processing of prosodic and syntactic information in spoken language. The aim was to investigate the long discussed relationship between prosody and syntax in online speech comprehension to reveal direct evidence about whether the two information types are interactive or independent from each other. The method of event-related potentials allowed us to sheet light on the precise time course of this relationship. Our experimental manipulation involved two prosodically different positions in German sentences, i.e., the critical noun in penultimate vs. final position. In syntactically correct sentences, a prosodic manipulation of the penultimate word gave rise to a late centroparietal negativity that resembled the classical N400 component. We interpreted the negativity as a correlate of lexical integration costs for the prosodically unexpected sentence-final word. Comparisons with syntactically incorrect sentences revealed that this effect was dependent on the sentences' grammatical correctness. When the prosodic manipulation was realized at the final word, we observed a right anterior negativity followed by a late positivity (P600). The right anterior negativity was present independent of the sentences' grammatical correctness. However, the P600 was not, as a late positivity was present for straightforward prosodic and syntactic violations but increased for the combined violations. This suggests that the right anterior negativity, and not the P600, should be considered as a pure prosodic effect. The combined data moreover suggest an interaction between prosody and syntax in a later time window during sentence comprehension.

Language disorder in schizophrenia as a developmental learning disorder

Receptive language disorder in schizophrenia is hypothesized to represent a learning disorder that involves a neurodevelopmental etiology. It is argued that a preexisting developmental language disorder may characterize a subset of schizophrenia patients. A primary deficit in the temporal dynamics of brain function is assumed to cause receptive language disorder in schizophrenia. This hypothesized core deficit includes both disturbance in the processing of rapid, sequential information and disruptions to patterns of brain activation and synchronization. These timing deficits may alter the way associative connections are formed and/or accessed in semantic memory. It is suggested that abnormalities in second-messenger pathways of subcortical-cortical circuitry offer an etiological nexus for language dysfunction in schizophrenia and developmental dyslexia.