Brain activity during syntactic and semantic processing--a magnetoencephalographic study

Drawings of objects were presented in series of 54 each to 14 German speaking subjects with the tasks to indicate by button presses a) whether the grammatical gender of an object name was masculine ("der") or feminine ("die") and b) whether the depicted object was man-made or nature-made. The magnetoencephalogram (MEG) was recorded with a whole-head neuromagnetometer and task-specific patterns of brain activity were determined in the source space (Minimum Norm Estimates, MNE). A left-temporal focus of activity 150-275 ms after stimulus onset in the gender decision compared to the semantic classification task was discussed as indicating the retrieval of syntactic information, while a more expanded left hemispheric activity in the gender relative to the semantic task 300-625 ms after stimulus onset was discussed as indicating phonological encoding. A predominance of activity in the semantic task was observed over right fronto-central region 150-225 ms after stimulus-onset, suggesting that semantic and syntactic processes are prominent in this stage of lexical selection.     

The influence of semantic and phonological factors on syntactic decisions: an event-related brain potential study

During language production and comprehension, information about a word's syntactic properties is sometimes needed. While the decision about the grammatical gender of a word requires access to syntactic knowledge, it has also been hypothesized that semantic (i.e., biological gender) or phonological information (i.e., sound regularities) may influence this decision. Event-related potentials (ERPs) were measured while native speakers of German processed written words that were or were not semantically and/or phonologically marked for gender. Behavioral and ERP results showed that participants were faster in making a gender decision when words were semantically and/or phonologically gender marked than when this was not the case, although the phonological effects were less clear. In conclusion, our data provide evidence that even though participants performed a grammatical gender decision, this task can be influenced by semantic and phonological factors.     

Sentence comprehension in Alzheimer's disease

A visual sentence‐picture matching task was used to clarify the nature of the comprehension deficit in Alzheimer's Disease (AD). Test sentences varied according to how crucial the processing of syntax was in computing a correct interpretation. Half the sentences could be understood through the comprehension of semantic cues alone; the other half required the processing of syntactic cues. In the first experiment, sentences were removed from view before the test pictures were presented; in the second, sentences and pictures were presented together to decrease demands on working memory. Two factors determined the accuracy of sentence comprehension: whether a syntactic analysis was needed and whether additional working‐memory resources were needed for temporary storage. When storage demands were minimized, patients were able to use semantic cues to guide comprehension. When semantic cues were unavailable, comprehension was impaired, regardless of whether or not there were additional storage requirements, providing evidence for a genuine syntactic deficit that is not due to coexisting semantic impairment or working‐memory dysfunction.     

Sentence comprehension in semantic dementia: a longitudinal case study

Sentence comprehension abilities were investigated in a patient with semantic dementia who was administered tests of semantic knowledge and sentence comprehension over a 5-year period. Results showed that despite a severe and continual degradation in semantic knowledge, syntactic comprehension abilities remained largely intact. Evidence was also found for a codependency between semantics and syntax in a task in which knowledge about conceptual number influenced subject-verb agreement in the patient and in control participants. Results are discussed in relation to the nature of the sentence comprehension impairment in semantic dementia and with reference to the modularity of the components of the language processing system.     

Event-related potentials suggest early interaction between syntax and semantics during on-line sentence comprehension

Event-related potentials (ERPs) were used to investigate interaction between syntactic parsing and semantic integration processes during a visual sentence comprehension task. The linguistic stimuli were Finnish five-word sentences containing morphosyntactic and/or semantic violations. Single morphosyntactic violations evoked left anterior negativity (LAN) and P600 components. Single semantic violations elicited a robust N400 effect over the left hemisphere. A later and weaker N400-like response was also observed in the right hemisphere, left-right hemispheric latency difference being 40 ms. Combined morphosyntactic and semantic violations elicited a P600 component and a negative ERP component within the latency range of the LAN and N400 components. Further analysis of these ERP effects provided evidence for early processual interaction between syntax and semantics during on-line sentence comprehension. The hemispheric distribution of the LAN and N400 components was taken to suggest lateralization of initial morphosyntactic parsing and semantic integration processes to the left hemisphere. In contrast, the later syntax-related P600 component was observed as being more pronounced over the posterior areas of the right hemisphere.     

The neuropsychology of sentence processing: Where do we stand?

In the early 1980s, sentence comprehension deficits were attributed to a loss of syntactic knowledge in agrammatic Broca's aphasics and to a short-term memory deficit in conduction aphasics. Findings in the remainder of the decade called both of these claims into question and presented general difficulties for the group study approach. Results from case studies support the representational independence of syntactic and semantic information but the interaction of these knowledge sources during processing. Working memory is still considered to provide critical constraints on sentence comprehension, but the capacity involved appears to be largely independent of the phonological storage involved in word list recall. Current computational approaches to sentence comprehension provide the means of accounting for the interaction of multiple sources of information and working memory requirements, but have yet to be tested against neuropsychological findings.     

Sentence comprehension in semantic dementia: a longitudinal case study

Abstract

Sentence comprehension abilities were investigated in a patient with semantic dementia who was administered tests of semantic knowledge and sentence comprehension over a 5-year period. Results showed that despite a severe and continual degradation in semantic knowledge, syntactic comprehension abilities remained largely intact. Evidence was also found for a codependency between semantics and syntax in a task in which knowledge about conceptual number influenced subject-verb agreement in the patient and in control participants. Results are discussed in relation to the nature of the sentence comprehension impairment in semantic dementia and with reference to the modularity of the components of the language processing system.     

MEG study on neural activities associated with syntactic and semantic violations in spoken Korean sentences

We carried out an magnetoencephalography (MEG) study to record cortical responses elicited in the left hemisphere by ending verb phrases, which had syntactic or semantic anomalies, in Korean sentences of subject-object-verb order. Using the high temporal and spatial resolution of MEG, the study was aimed at identifying neural activities that occur during a latency course associated with the syntactic or semantic process in the spoken sentence. Major responses, distinct from the responses to normal sentences, were observed in two latency periods of about 400 and 600 ms following the onset of the verb phrase. Source localization of the grand average fields indicated separate activities in the inferior frontal region and the vicinity of the auditory cortex for the first 400-ms response to the syntactic anomaly. The region around the auditory cortex was indicated for the response to the semantic anomaly in a similar latency. The second 600-ms response indicated activity around the middle temporal gyrus inferior to the auditory cortex for both syntactic and semantic anomalies. The results are discussed with reference to the ERP components established for Indo-European languages, and the possibility of concurrent processing of syntactic and semantic aspects is suggested.     

Functional segregation of the inferior frontal gyrus for syntactic processes: a functional magnetic-resonance imaging study

We used functional magnetic resonance imaging in 18 normal volunteers to determine whether there is separate representation of syntactic, semantic, and verbal working memory processing in the left inferior frontal gyrus (GFi). We compared a sentence comprehension task with a short-term memory maintenance task to identify syntactic and semantic processing regions. To investigate the effects of syntactic and verbal working memory load while minimizing the differences in semantic processes, we used comprehension tasks with garden-path (GP) sentences, which require re-parsing, and non-garden-path (NGP) sentences. Compared with the short-term memory task, sentence comprehension activated the left GFi, including Brodmann areas (BAs) 44, 45, and 47, and the left superior temporal gyrus. In GP versus NGP sentences, there was greater activity in the left BAs 44, 45, and 46 extending to the left anterior insula, the pre-supplementary motor area, and the right cerebellum. In the left GFi, verbal working memory activity was located more dorsally (BA 44/45), semantic processing was located more ventrally (BA 47), and syntactic processing was located in between (BA 45). These findings indicate a close relationship between semantic and syntactic processes, and suggest that BA 45 might link verbal working memory and semantic processing via syntactic unification processes.     

EEG Alpha: Lateral Asymmetry Related to Task, and Hypnotizability

Occipital EEG alpha (8-13 Hz) was recorded separately from the right and left hemispheres of 26 right-handed subjects during analytic (verbal and numerical) tasks, spatial (imagery) tasks, a music task, and a hypnotic susceptibility scale. An alpha laterality score was derived by computing the percent difference in the amplitude of alpha in the two hemispheres. This laterality score was significantly different between the analytic and spatial tasks, and between an eyes-open baseline and an eyes-open measurement during hypnotic amnesia. Because the spatial tasks used in this study are considered “easier” than the analytic or music tasks, the role of task difficulty provides some ambiguity in interpretation. Highly hypnotizable subjects showed significantly more alpha activity (compared to low hypnotizables) in all conditions (both outside hypnosis and within it) except for the eyes-open baseline and the eyes-open measurement following the release of amnesia. No differences were found between low- and high-hypnotizables in the laterality measure. This suggests that the lateral asymmetry of alpha is a function of task rather than of any particular cognitive style that may characterize the hypnotically susceptible. That high hypnotizables showed higher amplitudes of alpha, however, suggests that the overall production of alpha may be positively related to the particular cognitive style that characterizes the person who is able to experience hypnotic phenomena.     

Behavioural and electrodermal measures of lateralization for music perception in musicians and nonmusicians

Two groups of students, musicians and nonmusicians were tested on a dichotic listening forced choice recognition task with concurrent recording of bilateral electrodermal activity. Stimuli were excerpts of Bach 4-part chorales; probes were the soprano, bass, harmony or the chorale excerpt, with or without changed notes. Laterality effects in recognition and the GSR were obtained only in musicians as a function of the complexity of the task. It was concluded that styles of information processing assumed by the hemispheres are the consequence of an interaction between the stimulus and the state of the organism at the moment, such that the direction of laterality can change within a subject performing the same task depending upon its perceptual demand.     

Left cytoarchitectonic area 44 supports selection in the mental lexicon during language production

This functional magnetic resonance imaging (fMRI) study investigated the role of Broca’s region for selecting semantic, syntactic, and phonological information during picture naming. According to psycholinguistic theory, selection is reflected in speech latency differences, e.g. during priming. Here, homogenous (priming) blocks in which German picture names had the same semantic category, syntactic gender, or initial phoneme alternated with heterogeneous (non-priming) blocks. Speech latencies revealed a negative priming effect. Speech latencies were used as regressors for the fMRI data in order to tap selection processes. In Broca’s region (BA 44), among others, fMRI data showed repetition priming, which was positive for semantic and syntactic but negative for phonological selection. The different effects in area 44 are discussed in terms of psycholinguistic theory. Overall, the activation pattern is in line with the hypothesis that area 44 generally supports selection processes during noun production at several levels of the mental lexicon.     

A controlled study of processing of semantic and syntactic information in Alzheimer's disease.

Several previous studies have suggested a possible dissociation in the ability of patients with Alzheimer's Disease (AD) to utilize syntactic versus semantic information. This report describes a controlled experimental investigation of AD subjects' ability to process syntactic and semantic information. Thirteen mildly and moderately impaired AD patients were compared with 17 age- and education-matched elderly controls. Two tasks required subjects to identify and correct sentential errors; a third was a homophone spelling task. Results of the first task indicated that AD subjects were equivalent to controls in their ability to detect various types of sentential errors. When performing the second task, AD subjects were impaired in their ability to correct both types of errors, although there was a tendency for better performance with syntactically-based corrections. The third (homophone-spelling) task did not reveal a statistically significant differential sensitivity of AD subjects to syntactic versus semantic information. However, there was again a tendency for the former to be more easily processed. Results are discussed in terms of possible mechanisms which may underlie variations in the language-related performance of AD subjects.     

An influence of syntactic and semantic variables on word form retrieval

We report the case of DPI, an aphasic patient who shows a phonological impairment in production that spares certain syntactic and semantic categories. On a picture naming task, he produces mostly phono-logical paraphasias, and the probability of producing a correct response depends on the frequency and length of the target word. This deficit occurs in the presence of spared ability to find the grammatical gender of the items that he cannot name, intact conceptual knowledge, and very good reading and word repetition. Therefore, we conclude that DPI's deficit is restricted to the phonological retrieval of a correctly selected lexical entry. However, production errors are not uniform across semantic and syntactic domains. Numerals and names of days and months are totally spared compared to matched controls. In addition, abstract nouns and verbs are significantly less affected than concrete nouns, even when variables affecting phonological retrieval (frequency, length, syllabic structure) are controlled for. This suggests that a functional organisation in terms of semantic and syntactic variables exists at the level of phonological retrieval. We discuss these findings in light of current models of speech production.     

The Differentiating Activity of Monkey Putamen Neurons during Performance of Alternative Spatial Selection

Spike activity was recorded from three zones of the putamen in monkeys trained to bimanual operant activity during performance of an alternative spatial selection task. Neuron responses were analyzed using the following criteria: a) differentiation of the side providing reinforcement (differentiating/non-differentiating responses); b) response duration (tonic/phasic); c) response laterality (contralateral/ipsilateral hemispheres); d) baseline activity frequency. The differentiating activity of cells was found to show the closest correlation with behavioral aspects of the program, particularly the tonic part and, even more so, contralateral tonic responses. It is suggested that differentiating activity, as opposed to non-differentiating activity, is less a reflection of the morphological and neurochemical characteristics of the neural elements of the putamen than of their functional homogeneity in relation to external determinants of behavior.     

Dissociation of functions in a case of transcortical sensory aphasia

A patient is described who presents fluent speech, auditory comprehension deficit, and relatively intact sentence repetition. Performance on word-picture matching, attribute judgements, picture naming, naming from definition, and describing objects from their names indicates a selective deficit to the semantic system. Sentence repetition performance, which was affected by syntactic variables and tended to preserve grammatical structure, was interpreted as an indication of relatively intact syntactic and phonological processing abilities. The implications of this dissociation of semantics from syntax and phonology is discussed, and the nature of the semantic system that could give rise to these symptoms is considered.     

Verb production in the nonfluent and semantic variants of primary progressive aphasia: The influence of lexical and semantic factors

Differential patterns of impairment with respect to noun and verb production have been observed in the nonfluent and semantic variants of primary progressive aphasia. However, the factors influencing this discrepancy remain unclear. The present study evaluates verb retrieval in primary progressive aphasia using a naming task and a story completion task. Findings indicate that patients with the semantic variant are influenced by familiarity, frequency, and age of acquisition in both object and action naming, whereas patients with the nonfluent variant are not. Surprisingly, there were no differences in either group between object and action naming, presumably because the lists were well matched on pertinent variables. In the story completion task, greater impairment in semantically heavier than in semantically lighter verbs was observed for the semantic variant, and grammaticality and verb tense agreement was significantly lower in the nonfluent variant. The present findings suggest that lexicosemantic attributes affect verb production in the semantic variant, whereas both lexicosemantic and syntactic attributes affect verb production in the nonfluent variant.     

Creativity,schizotypy, and laterality

Introduction. Previous research has found associations between creativity (or semantic association), schizotypy, and laterality when each of the three pairings has been studied individually, leading to three relatively distinct bodies of literature. Methods. This study attempted to integrate previous research by providing measures of all three constructs in a within subjects correlational design. Participants were 30 undergraduate students who completed four measures of creativity, three schizotypy scales, and a lateralised lexical decision task. Signal detection theory (SDT) was used to analyse the laterality data. Results. Normal individuals with relatively lower SDT response criteria for stimuli presented to the left visual field/right hemisphere had higher schizotypy scores and higher performance on a verbal creativity test. Conclusions. These results extend previous findings by using SDT analyses to show for the first time that individuals scoring higher on certain schizotypy and creativity tests exhibited differences in response criteria to more readily accept right hemisphere responses, rather than exhibiting hemispheric differences in sensitivity (ability). The findings accord with theories proposing that higher schizotypy and creativity may partly arise from a lowering of criteria for evidence and/or from a shift to reliance on processing strategies that are more dependent on the right cerebral hemisphere.     

The P3b and P600(s): Positive contributions to language comprehension

Since its discovery in the 1960s, the P300 has been contributing both directly and indirectly to language research. Perhaps most notably, it has been suggested that the P600, an ERP component that was first characterized in the context of syntactic processing, could be a variant of the P3b subcomponent of the P300. Here, we review studies on both sides of the debate. We also review the “semantic P600,” a positivity with a similar time course and distribution to the P600 seen for syntactic manipulations but that is obtained in response to some types of semantic anomalies. Because most current theories of the P600 try to account for both the syntactic and the semantic variant, linking the syntactic P600 to the P3b might also imply a similar link for the semantic P600. However, we describe emerging research in our lab that casts doubt on the idea that the syntactic P600 and the semantic P600 are the same effect. We argue that grouping ERP responses primarily by domain (language vs. nonlanguage) is likely to be misleading and suggest alternative ways of determining whether ERP effects reflect similar or different processing mechanisms.     

A case for conflict across multiple domains: Memory and language impairments following damage to ventrolateral prefrontal cortex

Patients with focal lesions to the left inferior frontal gyrus (LIFG; BA 44/45) exhibit difficulty with language production and comprehension tasks, although the nature of their impairments has been somewhat difficult to characterize. No reported cases suggest that these patients are Broca's aphasics in the classic agrammatic sense. Recent case studies, however, do reveal a consistent pattern of deficit regarding their general cognitive processes: They are reliably impaired on tasks in which conflicting representations must be resolved by implementing top-down cognitive control (e.g., Stroop; memory tasks involving proactive interference). In the present study, we ask whether the language production and comprehension impairments displayed by a patient with circumscribed LIFG damage can best be understood within a general conflict resolution deficit account. We focus on one patient in particular—patient I.G.—and discuss the implications for language processing abilities as a consequence of a general cognitive control disorder. We compared I.G. and other frontal patients to age-matched control participants across four experiments. Experiment 1 tested participants' general conflict resolution abilities within a modified working memory paradigm in an attempt to replicate prior case study findings. We then tested language production abilities on tasks of picture naming (Experiment 2) and verbal fluency (Experiment 3), tasks that generated conflict at the semantic and/or conceptual levels. Experiment 4 tested participants' sentence processing and comprehension abilities using both online (eye movement) and offline measures. In this task, participants carried out spoken instructions containing a syntactic ambiguity, in which early interpretation commitments had to be overridden in order to recover an alternative, intended analysis of sentence meaning. Comparisons of I.G.'s performance with frontal and healthy control participants supported the following claim: I.G. suffers from a general conflict resolution impairment, which affects his ability to produce and comprehend language under specific conditions—namely, when semantic, conceptual, and/or syntactic representations compete and must be resolved.