Auditory language comprehension: an event-related fMRI study on the processing of syntactic and lexical information

The functional specificity of different brain areas recruited in auditory language processing was investigated by means of event-related functional magnetic resonance imaging (fMRI) while subjects listened to speech input varying in the presence or absence of semantic and syntactic information. There were two sentence conditions containing syntactic structure, i.e., normal speech (consisting of function and content words), syntactic speech (consisting of function words and pseudowords), and two word-list conditions, i.e., real words and pseudowords. The processing of auditory language, in general, correlates with significant activation in the primary auditory cortices and in adjacent compartments of the superior temporal gyrus bilaterally. Processing of normal speech appeared to have a special status, as no frontal activation was observed in this case but was seen in the three other conditions. This difference may point toward a certain automaticity of the linguistic processes used during normal speech comprehension. When considering the three other conditions, we found that these were correlated with activation in both left and right frontal cortices. An increase of activation in the planum polare bilaterally and in the deep portion of the left frontal operculum was found exclusively when syntactic processes were in focus. Thus, the present data may be taken to suggest an involvement of the left frontal and bilateral temporal cortex when processing syntactic information during comprehension.     

The influence of language exposure on lexical and syntactic language processing

Previous literature has argued that proficient bilingual speakers often demonstrate monolingual-equivalent structural processing of language (e.g., the processing of structural ambiguities; Frenck-Mestre, 2002). In this paper, we explore this thesis further via on-line examination of the processing of syntactically complex structures with three populations: those who classify as monolingual native English speaker (MNES), those who classify as non-native English speakers (NNES), and those who calssify as bilingual native English speakers (BNES). On-line measures of processing of object-relative constructions demonstrated that both NNES and BNES have different patterns of performance as compared to MNES. Further, NNES and BNES speakers perform differently from one another in such processing. The study also examines the activation of lexical information in biasing contexts, and suggests that different processes are at work in the different type of bilinguals examined here. The nature of these differences and the implications for developing sensitive models of on-line language comprehension are developed and discussed.     

An event-related fMRI study of syntactic and semantic violations

We used event-related functional magnetic resonance imaging to identify brain regions involved in syntactic and semantic processing. Healthy adult males read well-formed sentences randomly intermixed with sentences which either contained violations of syntactic structure or were semantically implausible. Reading anomalous sentences, as compared to well-formed sentences, yielded distinct patterns of activation for the two violation types. Syntactic violations elicited significantly greater activation than semantic violations primarily in superior frontal cortex. Semantically incongruent sentences elicited greater activation than syntactic violations in the left hippocampal and parahippocampal gyri, the angular gyri bilaterally, the right middle temporal gyrus, and the left inferior frontal sulcus. These results demonstrate that syntactic and semantic processing result in nonidentical patterns of activation, including greater frontal engagement during syntactic processing and larger increases in temporal and temporo-parietal regions during semantic analyses.     

Tracking the continuity of language comprehension: computer mouse trajectories suggest parallel syntactic processing

Although several theories of online syntactic processing assume the parallel activation of multiple syntactic representations, evidence supporting simultaneous activation has been inconclusive. Here, the continuous and non-ballistic properties of computer mouse movements are exploited, by recording their streaming x, y coordinates to procure evidence regarding parallel versus serial processing. Participants heard structurally ambiguous sentences while viewing scenes with properties either supporting or not supporting the difficult modifier interpretation. The curvatures of the elicited trajectories revealed both an effect of visual context and graded competition between simultaneously active syntactic representations. The results are discussed in the context of 3 major groups of theories within the domain of sentence processing.     

Sentence processing strategies in healthy seniors with poor comprehension: an fMRI study

We used fMRI to examine patterns of brain recruitment in 22 healthy seniors, half of whom had selective comprehension difficulty for grammatically complex sentences. We found significantly reduced recruitment of left posterolateral temporal [Brodmann area (BA) 22/21] and left inferior frontal (BA 44/6) cortex in poor comprehenders compared to the healthy seniors with good sentence comprehension, cortical regions previously associated with language comprehension and verbal working memory, respectively. The poor comprehenders demonstrated increased activation of left prefrontal (BA 9/46), right dorsal inferior frontal (BA 44/6), and left posterior cingulate (BA 31/23) cortices for the grammatically simpler sentences that they understood. We hypothesize that these brain regions support an alternate, nongrammatical strategy for processing complex configurations of symbolic information. Moreover, these observations emphasize the crucial role of the left perisylvian network for grammatically guided sentence processing in subjects with good comprehension.     

Give and take: syntactic priming during spoken language comprehension

Syntactic priming during language production is pervasive and well-studied. Hearing, reading, speaking or writing a sentence with a given structure increases the probability of subsequently producing the same structure, regardless of whether the prime and target share lexical content. In contrast, syntactic priming during comprehension has proven more elusive, fueling claims that comprehension is less dependent on general syntactic representations and more dependent on lexical knowledge. In three experiments we explored syntactic priming during spoken language comprehension. Participants acted out double-object (DO) or prepositional-object (PO) dative sentences while their eye movements were recorded. Prime sentences used different verbs and nouns than the target sentences. In target sentences, the onset of the direct-object noun was consistent with both an animate recipient and an inanimate theme, creating a temporary ambiguity in the argument structure of the verb (DO e.g., Show the horse the book; PO e.g., Show the horn to the dog). We measured the difference in looks to the potential recipient and the potential theme during the ambiguous interval. In all experiments, participants who heard DO primes showed a greater preference for the recipient over the theme than those who heard PO primes, demonstrating across-verb priming during online language comprehension. These results accord with priming found in production studies, indicating a role for abstract structural information during comprehension as well as production.     

Activation of lexical and syntactic target language properties in translation

Is reading for translation equal to reading in monolingual contexts? Horizontal/parallel theories of translation propose that normal reading and reading for translation differ because the translator engages in partial reformulation while reading for translating the source text. In contrast, vertical/serial theories assume that the translators first extract the meaning of the message, and only then they proceed to reformulate it. In two experiments, we manipulated lexical and syntactic properties of the target language (TL) while translators read for repetition or for translation. On-line sentence comprehension was affected by the lexical frequency of words in the TL (Experiment 1) and the syntactic congruency between the source language (SL) and TL sentences (Experiment 2). However, the influence of lexical and syntactic TL properties was restricted to the reading for translation task. According to our results, the horizontal view of translation includes code-to-code links between the SL and TL involving at least the lexical and syntactic level of processing.     

Syntactic priming and the lexical boost effect during sentence production and sentence comprehension: An fMRI study

Behavioral syntactic priming effects during sentence comprehension are typically observed only if both the syntactic structure and lexical head are repeated. In contrast, during production syntactic priming occurs with structure repetition alone, but the effect is boosted by repetition of the lexical head. We used fMRI to investigate the neuronal correlates of syntactic priming and lexical boost effects during sentence production and comprehension. The critical measure was the magnitude of fMRI adaptation to repetition of sentences in active or passive voice, with or without verb repetition. In conditions with repeated verbs, we observed adaptation to structure repetition in the left IFG and MTG, for active and passive voice. However, in the absence of repeated verbs, adaptation occurred only for passive sentences. None of the fMRI adaptation effects yielded differential effects for production versus comprehension, suggesting that sentence comprehension and production are subserved by the same neuronal infrastructure for syntactic processing.     

Maintenance versus manipulation of information held in working memory: an event-related fMRI study.

One model of the functional organization of lateral prefrontal cortex (PFC) in primates posits that this region is organized in a dorsal/ventral fashion subserving spatial and object working memory, respectively. Alternatively, it has been proposed that a dorsal/ventral subdivision of lateral PFC instead reflects the type of processing performed upon information held in working memory. We tested this hypothesis using an event-related fMRI method that can discriminate among functional changes occurring during temporally separated behavioral subcomponents of a single trial. Subjects performed a delayed-response task with two types of trials in which they were required to: (1) retain a sequence of letters across the delay period (maintenance) or (2) reorder the sequence into alphabetical order across the delay period (manipulation). In each subject, activity during the delay period was found in both dorsolateral and ventrolateral PFC in both types of trials. However, dorsolateral PFC activity was greater in manipulation trials. These findings are consistent with the processing model of the functional organization of working memory in PFC.     

The lateralization of language comprehension using event-related potentials

Event-Related Potentials were recorded over occipital and parietal scalp from left- and right-handed adults presented with a language and a non-language visual stimulus using a divided field, "oddball" paradigm. The major finding of interest was that the P300 component was larger over the left than the right hemisphere of the right-handers when the language stimulus was presented to the left hemisphere; there were no hemispheric differences for the left-handers, regardless of field of presentation. These results are discussed in the context of developing noninvasive measures to lateralize language function.     

Dissociation between syntactic and semantic processing during idiom comprehension

Syntactic and semantic processing of literal and idiomatic phrases were investigated with a priming procedure. In 3 experiments, participants named targets that were syntactically appropriate or inappropriate completions for semantically unrelated sentence contexts. Sentences ended with incomplete idioms (kick the...) and were biased for either a literal (ball) or an idiomatic (bucket) completion. Syntactically appropriate targets were named more quickly than inappropriate ones for both contextual biases, suggesting that syntactic analysis occurs for idioms. In a final experiment, targets were either concrete (expected) or abstract (unexpected) nouns. For literal sentences, the abstract targets were named more slowly than the concrete targets. In contrast, there was no concreteness effect for idiomatic sentences, suggesting that the literal meaning of the idiom is not processed. Overall, the results provide evidence for dissociation between syntactic and semantic processing.     

Aging affects both perceptual and lexical/semantic components of word stem priming: An event-related fMRI study

In this event-related fMRI study, brain activity patterns were compared in extensive groups of young (N=25) and older (N=38) adults, while they were performing a word stem completion priming task. Based on behavioral findings, we tested the hypothesis that aging affects only the lexical/semantic, but not the perceptual component of word stem priming. To this end, we distinguished between priming-related activity reductions in posterior regions involved in visual processing, and regions associated with lexical/semantic retrieval processes, i.e., left lateral temporal and left prefrontal regions. Both groups revealed significant priming-related response time reductions. However, in accordance with earlier findings, a larger priming effect was found in the group of young participants. In line with previous imaging studies, the groups showed common priming-related activity reductions in the anterior cingulate, and the left inferior prefrontal cortex extending into the anterior portion of the left superior temporal gyrus, and at lower thresholds also in the right occipital lobe. However, when directly comparing the groups, greater priming-related reductions were found for the young group in the left anterior superior temporal gyrus and the right posterior occipital lobe. These findings suggest that, converse to current psychological views, aging affects both perceptual and lexical/semantic components of repetition priming.     

Non-target language processing in Chinese-English bilinguals: a study of event-related potential

The event-related brain potential (ERP) technique was used to investigate the neural mechanism of non-target language processing in Chinese-English bilinguals. Participants were presented with a mixed list of Chinese and English words and required to make conceptual decisions for words in one language and ignore words in the other non-target language. Regardless of whether the nontarget word was in Chinese or English, the ERPs they elicited were modulated by word frequency, suggesting that their meaning had been accessed. The N400 peak was delayed in the English as the non-target language condition, probably because participants were less proficient in English. The results suggest that the non-target language can be processed during conceptual tasks with participants' proficiency in this language being a critical factor.     

Eye movements and spoken language comprehension: effects of visual context on syntactic ambiguity resolution

When participants follow spoken instructions to pick up and move objects in a visual workspace, their eye movements to the objects are closely time-locked to referential expressions in the instructions. Two experiments used this methodology to investigate the processing of the temporary ambiguities that arise because spoken language unfolds over time. Experiment 1 examined the processing of sentences with a temporarily ambiguous prepositional phrase (e.g., "Put the apple on the towel in the box") using visual contexts that supported either the normally preferred initial interpretation (the apple should be put on the towel) or the less-preferred interpretation (the apple is already on the towel and should be put in the box). Eye movement patterns clearly established that the initial interpretation of the ambiguous phrase was the one consistent with the context. Experiment 2 replicated these results using prerecorded digitized speech to eliminate any possibility of prosodic differences across conditions or experimenter demand. Overall, the findings are consistent with a broad theoretical framework in which real-time language comprehension immediately takes into account a rich array of relevant nonlinguistic context.     

Language comprehension vs. language production: age effects on fMRI activation

Normal language acquisition is a process that unfolds with amazing speed primarily in the first years of life. However, the refinement of linguistic proficiency is an ongoing process, extending well into childhood and adolescence. An increase in lateralization and a more focussed productive language network have been suggested to be the neural correlates of this process. However, the processes underlying the refinement of language comprehension are less clear. Using a language comprehension (Beep Stories) and a language production (Vowel Identification) task in fMRI, we studied language representation and lateralization in 36 children, adolescents, and young adults (age 6-24 years). For the language comprehension network, we found a more focal activation with age in the bilateral superior temporal gyri. No significant increase of lateralization with age could be observed, so the neural basis of language comprehension as assessed with the Beep Stories task seems to be established in a bilateral network by late childhood. For the productive network, however, we could confirm an increase with age both in focus and lateralization. Only in the language comprehension task did verbal IQ correlate with lateralization, with higher verbal IQ being associated with more right-hemispheric involvement. In some subjects (24%), language comprehension and language production were lateralized to opposite hemispheres.     

Syntactic loss versus processing deficit: an assessment of two theories of agrammatism and syntactic comprehension deficits

This research evaluated Grodzinsky's (1984, 1986a) syntactic loss and Kolk and van Grunsven's (1985) working memory impairment explanations of syntactic comprehension deficits in agrammatic aphasics. Four aphasic patients were evaluated who showed different patterns of impairment on morphological and structural aspects of production. The comprehension tasks compared performance on full and truncated passive sentences. The syntactic loss hypothesis predicted worse performance on truncated than full passives, while the working memory deficit hypothesis predicted the reverse. Neither hypothesis was supported, as the patients performed at a similar level on both types of passives. In addition, there was little relation between the patients' production indices and their comprehension level. The results argue against any global theory of agrammatism that attempts to attribute all agrammatic speech and co-occurring syntactic comprehension deficits to the same source.     

Prosodic processing by children: an fMRI study

Prosodic information in the speech signal carries information about linguistic structure as well as emotional content. Although children are known to use prosodic information from infancy onward to assist linguistic decoding, the brain correlates of this skill in childhood have not yet been the subject of study. Brain activation associated with processing of linguistic prosody was examined in a study of 284 normally developing children between the ages of 5 and 18 years. Children listened to low-pass filtered sentences and were asked to detect those that matched a target sentence. fMRI scanning revealed multiple regions of activation that predicted behavioral performance, independent of age-related changes in activation. Likewise, age-related changes in task activation were found that were independent of differences in task accuracy. The overall pattern of activation is interpreted in light of task demands and factors that may underlie age-related changes in task performance.     

Effects of negative content on the processing of gender information: An event-related potential study

Previous research on emotion in language has mainly concerned the impact of emotional information on several aspects of lexico-semantic analyses of single words. However, affective influences on morphosyntactic processing are less understood. In the present study, we focused on the impact of negative valence in the processing of gender agreement relations. Event-related potentials (ERPs) were recorded while participants read three-word phrases and performed a syntactic judgment task. Negative and neutral adjectives could agree or disagree in gender with the preceding noun. At an electrophysiological level, the amplitude of a left anterior negativity (LAN) to gender agreement mismatches decreased in negative words, relative to neutral words. The behavioral data suggested that LAN amplitudes might be indexing the processing costs associated with the detection of gender agreement errors, since the detection of gender mismatches resulted in faster and more accurate responses than did the detection of correct gender agreement relations. According to this view, it seems that negative content facilitated the processes implicated in the early detection of gender agreement mismatches. However, gender agreement violations in negative words triggered processes involved in the reanalysis and repair of the syntactic structure, as reflected in larger P600 amplitudes to incorrect than to correct phrases, irrespective of their emotional valence.