Processing homonymy and polysemy: effects of sentential context and time-course following unilateral brain damage

Computed tomography findings as early predictors of long-term language impairment in patients with traumatic brain injury

This study aims to assess the relationship between computed tomography (CT) findings, during the acute phase of hospitalization, and long-term language impairment in people with traumatic brain injury (TBI). Another aim was to assess the receptive and expressive abilities of subjects with TBI based on the location of the injury. This is a retrospective observational study including 49 participants with TBI due to war injuries. The Arabic Diagnostic Aphasia Battery (A-DAB-1) was administered to the participants and the Helsinki CT score was computed to quantify brain damage. The results showed that the Helsinki CT score was negatively correlated with the total score of the A-DAB-1 (r = -0.544, p-value < 0.0001). Simple linear regression supported such findings and reflected an inversely proportional relationship between both variables (p-value < 0.0001). When compared with subjects having right hemisphere damage, subjects with left hemisphere and bilateral brain damage performed more poorly on language tasks respectively as follows: A-DAB-1 overall score (92.08-66.08-70.28, p-value = 0.021), Content of descriptive speech (9.57-6.69-7.22, p-value = 0.034), Verbal fluency (6.57-3.54-3.89, p-value = 0.002), Auditory comprehension (9.71-7.54-7.78, p-value = 0.039), Complex auditory commands (9.71-7.65-7.56, p-value = 0.043), Repetition (9.75-7.08-7.61, p-value = 0.036), Naming (9.93-7.15-8.11, p-value = 0.046). Following TBI, CT findings on admission can significantly predict long-term language abilities, with left side lesions inducing poorer outcomes.

Offline dominance and zeugmatic similarity normings of variably ambiguous words assessed against a neural language model (BERT)

For any research program examining how ambiguous words are processed in broader linguistic contexts, a first step is to establish factors relating to the frequency balance or dominance of those words' multiple meanings, as well as the similarity of those meanings to one other. Homonyms-words with divergent meanings-are one ambiguous word type commonly utilized in psycholinguistic research. In contrast, although polysemes-words with multiple related senses-are far more common in English, they have been less frequently used as tools for understanding one-to-many word-to-meaning mappings. The current paper details two norming studies of a relatively large number of ambiguous English words. In the first, offline dominance norming is detailed for 547 homonyms and polysemes via a free association task suitable for words across the ambiguity continuum, with a goal of identifying words with more equibiased meanings. The second norming assesses offline meaning similarity for a partial subset of 318 ambiguous words (including homonyms, unambiguous words, and polysemes divided into regular and irregular types) using a novel, continuous rating method reliant on the linguistic phenomenon of zeugma. In addition, we conduct computational analyses on the human similarity norming data using the BERT pretrained neural language model (Devlin et al., 2018, BERT: Pre-training of deep bidirectional transformers for language understanding. ArXiv Preprint. arXiv:1810.04805) to evaluate factors that may explain variance beyond that accounted for by dictionary-criteria ambiguity categories. Finally, we make available the summarized item dominance values and similarity ratings in resultant appendices (see supplementary material), as well as individual item and participant norming data, which can be accessed online ( https://osf.io/g7fmv/ ).

Selective Metaphor Impairments After Left, Not Right, Hemisphere Injury

The relative contributions of the left and right hemispheres to the processing of metaphoric language remains unresolved. Neuropsychological studies of brain-injured patients have motivated the hypothesis that the right hemisphere plays a critical role in understanding metaphors. However, the data are inconsistent and the hypothesis is not well-supported by neuroimaging research. To address this ambiguity about the right hemisphere's role, we administered a metaphor sentence comprehension task to 20 left-hemisphere injured patients, 20 right hemisphere injured patients, and 20 healthy controls. Stimuli consisted of metaphors of three different types: predicate metaphors based on action verbs, nominal metaphors based on event nouns, and nominal metaphors based on entity nouns. For each metaphor (n = 60), a closely matched literal sentence with the same source term was also generated. Each sentence was followed by four adjective-noun answer choices (target + three foil types) and participants were instructed to select the phrase that best matched the meaning of the sentence. As a group, both left and right hemisphere patients performed worse on metaphoric than literal sentences, and the degree of this difficulty varied for the different types of metaphor - but there was no difference between the two patient groups. Tests for literal-metaphor dissociations at the level of single cases revealed two types of impairments: general comprehension deficits affecting metaphors and literal sentences equally, and selective metaphor impairments that were specific to different types of metaphor. All cases with selective metaphor deficits had injury to the left hemisphere, and no known comprehension difficulties with literal language. Our results argue against the hypothesis of a specific or necessary contribution of the right hemisphere for understanding metaphoric language. Further, they reveal deficits in metaphoric language comprehension not captured by traditional language assessments, suggesting overlooked communication difficulties in left hemisphere patients.

Lexical Ambiguity Resolution Using Discourse Contexts in Persons With and Without Aphasia

PURPOSE

The purpose of this study was to investigate the ability of persons with aphasia (PWA) to resolve different types of ambiguous words (homophones, metaphors, and metonyms) in discourse contexts.

METHOD

Six PWA and 10 controls listened to short discourses that biased either the dominant (more frequent) or subordinate (less frequent) version of an ambiguous word as well as nonsense (filler) discourses. Participants then indicated whether or not the final sentence, which contained the ambiguity, made sense in the discourse. Data for both accuracy and reaction time were collected.

RESULTS

There was no significant Group × Word Type × Frequency interaction in the reaction time data. In the accuracy analysis, there was a significant Group × Frequency × Word Type interaction, which appeared to be driven by the PWA's relative accuracy with subordinate homophones and relative inaccuracy with subordinate metaphors.

CONCLUSIONS

These results suggest that PWA were able to use discourse contexts to resolve subordinate versions of literal ambiguous words but have difficulty resolving metaphoric ambiguous words. Further investigations should be done to clarify how much context PWA require to successfully resolve lexical ambiguities.

You may now kiss the bride: Interpretation of social situations by individuals with right or left hemisphere injury

While left hemisphere damage (LHD) has been clearly shown to cause a range of language impairments, patients with right hemisphere damage (RHD) also exhibit communication deficits, such as difficulties processing prosody, discourse, and social contexts. In the current study, individuals with RHD and LHD were directly compared on their ability to interpret what a character in a cartoon might be saying or thinking, in order to better understand the relative role of the right and left hemisphere in social communication. The cartoon stimuli were manipulated so as to elicit more or less formulaic responses (e.g., a scene of a couple being married by a priest vs. a scene of two people talking, respectively). Participants' responses were scored by blind raters on how appropriately they captured the gist of the social situation, as well as how formulaic and typical their responses were. Results showed that RHD individuals' responses were rated as significantly less appropriate than controls and were also significantly less typical than controls and individuals with LHD. Individuals with RHD produced a numerically lower proportion of formulaic expressions than controls, but this difference was only a trend. Counter to prediction, the pattern of performance across participant groups was not affected by how constrained/formulaic the social situation was. The current findings expand our understanding of the roles that the right and left hemispheres play in social processing and communication and have implications for the potential treatment of social communication deficits in individuals with RHD.

Voxel-Based Lesion Symptom Mapping of Coarse Coding and Suppression Deficits in Patients With Right Hemisphere Damage

PURPOSE

This study examined right hemisphere (RH) neuroanatomical correlates of lexical-semantic deficits that predict narrative comprehension in adults with RH brain damage. Coarse semantic coding and suppression deficits were related to lesions by voxel-based lesion symptom mapping.

METHOD

Participants were 20 adults with RH cerebrovascular accidents. Measures of coarse coding and suppression deficits were computed from lexical decision reaction times at short (175 ms) and long (1000 ms) prime-target intervals. Lesions were drawn on magnetic resonance imaging images and through normalization were registered on an age-matched brain template. Voxel-based lesion symptom mapping analysis was applied to build a general linear model at each voxel. Z score maps were generated for each deficit, and results were interpreted using automated anatomical labeling procedures.

RESULTS

A deficit in coarse semantic activation was associated with lesions to the RH posterior middle temporal gyrus, dorsolateral prefrontal cortex, and lenticular nuclei. A maintenance deficit for coarsely coded representations involved the RH temporal pole and dorsolateral prefrontal cortex more medially. Ineffective suppression implicated lesions to the RH inferior frontal gyrus and subcortical regions, as hypothesized, along with the rostral temporal pole.

CONCLUSION

Beyond their scientific implications, these lesion-deficit correspondences may help inform the clinical diagnosis and enhance decisions about candidacy for deficit-focused treatment to improve narrative comprehension in individuals with RH damage.

Flying under the radar: figurative language impairments in focal lesion patients

Despite the prevalent and natural use of metaphor in everyday language, the neural basis of this powerful communication device remains poorly understood. Early studies of brain-injured patients suggested the right hemisphere plays a critical role in metaphor comprehension, but more recent patient and neuroimaging studies do not consistently support this hypothesis. One explanation for this discrepancy is the challenge in designing optimal tasks for brain-injured populations. As traditional aphasia assessments do not assess figurative language comprehension, we designed a new metaphor comprehension task to consider whether impaired metaphor processing is missed by standard clinical assessments. Stimuli consisted of 60 pairs of moderately familiar metaphors and closely matched literal sentences. Sentences were presented visually in a randomized order, followed by four adjective-noun answer choices (target + three foil types). Participants were instructed to select the phrase that best matched the meaning of the sentence. We report the performance of three focal lesion patients and a group of 12 healthy, older controls. Controls performed near ceiling in both conditions, with slightly more accurate performance on literal than metaphoric sentences. While the Western Aphasia Battery (Kertesz, 1982) and the objects and actions naming battery (Druks and Masterson, 2000) indicated minimal to no language difficulty, our metaphor comprehension task indicated three different profiles of metaphor comprehension impairment in the patients’ performance. Single case statistics revealed comparable impairment on metaphoric and literal sentences, disproportionately greater impairment on metaphors than literal sentences, and selective impairment on metaphors. We conclude our task reveals that patients can have selective metaphor comprehension deficits. These deficits are not captured by traditional neuropsychological language assessments, suggesting overlooked communication difficulties.

Contextual Constraint Treatment for coarse coding deficit in adults with right hemisphere brain damage: generalisation to narrative discourse comprehension

Coarse coding is the activation of broad semantic fields that can include multiple word meanings and a variety of features, including those peripheral to a word's core meaning. It is a partially domain-general process related to general discourse comprehension and contributes to both literal and non-literal language processing. Adults with damage to the right cerebral hemisphere (RHD) and a coarse coding deficit are particularly slow to activate features of words that are relatively distant or peripheral. This manuscript reports a pre-efficacy study of Contextual Constraint Treatment (CCT), a novel, implicit treatment designed to increase the efficiency of coarse coding with the goal of improving narrative comprehension and other language performance that relies on coarse coding. Participants were four adults with RHD. The study used a single-subject controlled experimental design across subjects and behaviours. The treatment involved pre-stimulation, using a hierarchy of strong and moderately biased contexts, to prime the intended distantly related features of critical stimulus words. Three of the four participants exhibited gains in auditory narrative discourse comprehension, the primary outcome measure. All participants exhibited generalisation to untreated items. No strong generalisation to processing non-literal language was evident. The results indicate that CCT yields both improved efficiency of the coarse coding process and generalisation to narrative comprehension.

Pathways to lexical ambiguity: fMRI evidence for bilateral fronto-parietal involvement in language processing

Numerous functional neuroimaging studies reported increased activity in the pars opercularis and the pars triangularis (Brodmann's areas 44 and 45) of the left hemisphere during the performance of linguistic tasks. The role of these areas in the right hemisphere in language processing is not understood and, although there is evidence from lesion studies that the right hemisphere is involved in the appreciation of semantic relations, no specific anatomical substrate has yet been identified. This event-related functional magnetic resonance imaging study compared brain activity during the performance of language processing trials in which either dominant or subordinate meaning activation of ambiguous words was required. The results show that the ventral part of the pars opercularis both in the left and the right hemisphere is centrally involved in language processing. In addition, they highlight the bilateral co-activation of this region with the supramarginal gyrus of the inferior parietal lobule during the processing of this type of linguistic material. This study, thus, provides the first evidence of co-activation of Broca's region and the inferior parietal lobule, succeeding in further specifying the relative contribution of these cortical areas to language processing.

Studies on semantic priming effects in right hemisphere stroke: A systematic review

The role of the right cerebral hemisphere (RH) associated with semantic priming effects (SPEs) must be better understood, since the consequences of RH damage on SPE are not yet well established.

Suppression and narrative time shifts in adults with right-hemisphere brain damage

PURPOSE

This study examined the functioning of a central comprehension mechanism, suppression, in adults with right-hemisphere damage (RHD) while they processed narratives that cued a shift in time frame. In normal language comprehension, mental activation of concepts from a prior time frame is suppressed. The (re)activation of information following a time frame shift was also assessed.

METHOD

Twenty adults (12 RHD; 8 non brain-damaged) completed a speeded word recognition task while listening to narratives in 2 conditions: shift ("an hour later") and no shift ("a moment later").

RESULTS

There was no group difference in suppression for response time proportion data (shift/no shift), but cluster analyses identified a suppression deficit in 8 of the adults with RHD. There was overlap in suppression function at the narrative and lexical levels. The group with RHD was significantly delayed in mentally (re)activating new information after a time shift cue.

CONCLUSION

Results underscore the generality of suppression functioning in adults with RHD. As such, treatment for a suppression deficit at one level may generalize to another level. An apparent independence of suppression and activation deficits suggests that each may need separate treatment. A better understanding of the nature and boundary conditions of suppression and activation deficits should better inform clinical decisions.

Not all ambiguous words are created equal: an EEG investigation of homonymy and polysemy

Event-related potentials (ERPs) were used to investigate the time-course of meaning activation of different types of ambiguous words. Unbalanced homonymous ("pen"), balanced homonymous ("panel"), metaphorically polysemous ("lip"), and metonymically polysemous words ("rabbit") were used in a visual single-word priming delayed lexical decision task. The theoretical distinction between homonymy and polysemy was reflected in the N400 component. Homonymous words (balanced and unbalanced) showed effects of dominance/frequency with reduced N400 effects predominantly observed for dominant meanings. Polysemous words (metaphors and metonymies) showed effects of core meaning representation with both dominant and subordinate meanings showing reduced N400 effects. Furthermore, the division within polysemy, into metaphor and metonymy, was supported. Differences emerged in meaning activation patterns with the subordinate meanings of metaphor inducing differentially reduced N400 effects moving from left hemisphere electrode sites to right hemisphere electrode sites, potentially suggesting increased involvement of the right hemisphere in the processing of figurative meaning.

Generalization of a Novel, Implicit Treatment for Coarse Coding Deficit in Right Hemisphere Brain Damage: A Single Subject Experiment

BACKGROUND: This manuscript reports generalization effects of Contextual Constraint Treatment for an adult with right hemisphere brain damage (RHD). Contextual Constraint Treatment is designed to stimulate inefficient language comprehension processes implicitly, by providing linguistic context to prime, or constrain, the intended interpretations of treatment stimuli. The study participant had a coarse coding deficit, defined as delayed mental activation of particularly distant semantic features of words (e.g., rotten as a feature of "apple"). Treatment effects were expected to generalize to auditory comprehension of narrative discourse, and perhaps to figurative language interpretation, because coarse coding has been hypothesized and/or demonstrated to support these abilities. AIMS: This treatment study aimed to induce generalization of Contextual Constraint Treatment in an adult with RHD with inefficient coarse coding. METHODS #ENTITYSTARTX00026; PROCEDURES: The participant in this study was a 75 year old man with RHD and a coarse coding deficit. A single subject experimental design across behaviors (stimulus lists) was used to document performance in baseline, treatment, and follow-up phases. Treatment consisted of providing brief, spoken context sentences to prestimulate, or constrain, intended interpretations of stimulus items. The participant made no explicit associations or metalinguistic judgments about the constraint sentences or stimulus words; rather, these contexts served only as implicit primes. Probe tasks were adapted from prior work on coarse coding in RHD. The dependent measure was the percentage of responses that met predetermined response time criteria. There were two levels of contextual constraint, Strong and Moderate. Treatment for each item began with the provision of the Strong constraint context, to minimize the production or reinforcement of erroneous or exceedingly slow responses. Generalization was assessed to a well-standardized measure of narrative discourse comprehension and to several metalinguistic tasks of figurative language interpretation. OUTCOMES #ENTITYSTARTX00026; RESULTS: Treatment-contingent gains, associated with respectable effect sizes, were evident after a brief period of treatment on one stimulus list. Generalization occurred to untrained items, suggesting that the treatment was facilitating the underlying coarse coding process. Most importantly, generalization was evident to narrative comprehension performance, for both overall accuracy and accuracy answering questions about implied information, and all of these gains maintained through three follow-up sessions. CONCLUSIONS: Though the results are still preliminary, this single-subject experimental design documents the potential for meaningful gains from a novel treatment that implicitly targets an underlying language comprehension process in an adult with RHD.

Neural correlates of metonymy resolution

Metonymies are exemplary models for complex semantic association processes at the sentence level. We investigated processing of metonymies using event-related functional magnetic resonance imaging (fMRI). During an 1.5Tesla fMRI scan, 14 healthy subjects (12 female) read 124 short German sentences with either literal (like "Africa is arid"), metonymic ("Africa is hungry"), or nonsense ("Africa is woollen") content. Sentences were constructed so that they obey certain grammatical, semantic, and plausibility conditions and were matched for word frequency, semantic association, length and syntactic structure. We concentrated on metonymies that were not yet fossilised; we also examined a wide variety of metonymic readings. Reading metonymies relative to literal sentences revealed signal changes in a predominantly left-lateralised fronto-temporal network with maxima in the left and right inferior frontal as well as left middle temporal gyri. Left inferior frontal activation may reflect both inference processes and access to world knowledge during metonymy resolution.

Event-related potentials reveal the effects of aging on meaning selection and revision

ERPs were recorded as older adults decided if a target word was related to a lateralized ambiguous or unambiguous prime; prime-target pairs were preceded by a related or unrelated context word. In an unrelated context, N400 facilitation effects differed from those seen in young adults, with older adults showing priming for the dominant meaning (e.g., BOOM-BANK-DEPOSIT) on right visual field/left hemisphere (RVF/LH) trials and priming for the subordinate meaning (e.g., BOOM-BANK-RIVER) on LVF/RH trials. Higher-functioning older adults, especially those with better inhibition, were more likely to show bilateral activation of the dominant meaning and unilateral activation of the subordinate meaning, suggesting a retention of young-like activation. In a biasing context (e.g., RIVER-BANK-DEPOSIT), older adults selected the contextually-consistent meaning, but were less likely than young adults to revise their selection.

Automatic and controlled aspects of lexical associative processing in the two cerebral hemispheres

Associative processing in the cerebral hemispheres was examined using ERPs and visual half-field (VF) methods. Associative strength was manipulated using asymmetrically associated pairs: viewed in one order (forward), there was a strong prime-to-target association, but in the backward order, predictability was weak. N400 priming was greater for forward than backward pairs in both VFs and not different across VF, suggesting similar semantic representations and automatic meaning activation in the two hemispheres. However, a frontal P2 enhancement for forward pairs restricted to the LH suggests that it uses context to predict likely upcoming words. Also, greater late positive complex priming for backward pairs in the LH than the RH reveals a LH advantage for strategically reshaping meaning activation for weakly related and/or non-canonically ordered pairs. The results link asymmetries in word processing with those observed at the sentence level.

Discourse Impairments Following Right Hemisphere Brain Damage: A Critical Review

Right hemisphere brain damage (RHD) rarely causes aphasias marked by clear and widespread failures of comprehension or extreme difficulty producing fluent speech. Nonetheless, subtle language comprehension deficits can occur following unilateral RHD. In this article, we review the empirical record on discourse function following right hemisphere damage, as well as relevant work on non-brain damaged individuals that focuses on right hemisphere function. The review is divided into four sections that focus on discourse processing, inferencing, humor, and non-literal language. While the exact role that the right hemisphere plays in language processing, and the exact way that the two cerebral hemispheres coordinate their linguistic processes are still open to debate, our review suggests that the right hemisphere plays a critical role in managing inferred or implied information by maintaining relevant information and/or suppressing irrelevant information. Deficits in one or both of these mechanisms may account for discourse deficits following RHD.

Theoretical Considerations for Understanding "Understanding" by Adults With Right Hemisphere Brain Damage

This article reviews and evaluates leading accounts of narrative comprehension deficits in adults with focal damage to the right cerebral hemisphere (RHD). It begins with a discussion of models of comprehension, which explain how comprehension proceeds through increasingly complex levels of representation. These models include two phases of comprehension processes, broad activation of information as well as pruning and focusing interpretation of meaning based on context. The potential effects of RHD on each processing phase are reviewed, focusing on factors that range from relatively specific (e.g., how the right versus the left hemisphere activate word meanings; how the right hemisphere is involved in inferencing) to more general (the influence of cognitive resource factors; the role of suppression of contextually-irrelevant information). Next, two specific accounts of RHD comprehension difficulties, coarse coding and suppression deficit, are described. These have been construed as opposing processes, but a possible reconciliation is proposed related to the different phases of comprehension and the extent of meaning activation. Finally, the article addresses the influences of contextual constraint on language processing and the continuity of literal and nonliteral language processing, two areas in which future developments may assist our clinical planning.

The basal ganglia circuits, dopamine, and ambiguous word processing: a neurobiological account of priming studies in Parkinson's disease

Research into the processing of lexical ambiguities has provided a valuable paradigm for investigating the functional architecture of the language processing system in normal and neurologically impaired populations and specifically, how basal ganglia circuits and the neurotransmitter dopamine may act to enhance and/or suppress various meanings relative to the context in which the lexical ambiguity appears. In this review, we develop the hypothesis that an integrated basal ganglia thalamocortical circuit linking the striatum and inferior frontal cortex is involved in the enhancement and suppression of ambiguous word meanings when a lexical ambiguity is presented within a linguistic context. Reference to behavioral, neurophysiological, and neurochemical studies of subcortical function in both healthy populations and people with Parkinson's disease will be used to provide further support for the proposal that the subcortex is integrally involved in ambiguous word processing.

Coarse coding and discourse comprehension in adults with right hemisphere brain damage

BACKGROUND: Various investigators suggest that some discourse-level comprehension difficulties in adults with right hemisphere brain damage (RHD) have a lexical-semantic basis. As words are processed, the intact right hemisphere arouses and sustains activation of a wide-ranging network of secondary or peripheral meanings and features-a phenomenon dubbed "coarse coding". Coarse coding impairment has been postulated to underpin some prototypical RHD comprehension deficits, such as difficulties with nonliteral language interpretation, discourse integration, some kinds of inference generation, and recovery when a reinterpretation is needed. To date, however, no studies have addressed the hypothesised link between coarse coding deficit and discourse comprehension in RHD. AIMS: The current investigation examined whether coarse coding was related to performance on two measures of narrative comprehension in adults with RHD. METHODS #ENTITYSTARTX00026; PROCEDURES: Participants were 32 adults with unilateral RHD from cerebrovascular accident, and 38 adults without brain damage. Coarse coding was operationalised as poor activation of peripheral/weakly related semantic features of words. For the coarse coding assessment, participants listened to spoken sentences that ended in a concrete noun. Each sentence was followed by a spoken target phoneme string. Targets were subordinate semantic features of the sentence-final nouns that were incompatible with their dominant mental representations (e.g., "rotten" for apple). Targets were presented at two post-noun intervals. A lexical decision task was used to gauge both early activation and maintenance of activation of these weakly related semantic features. One of the narrative tasks assessed comprehension of implied main ideas and details, while the other indexed high-level inferencing and integration. Both comprehension tasks were presented auditorily. For all tasks, accuracy of performance was the dependent measure. Correlations were computed within the RHD group between both the early and late coarse coding measures and the two discourse measures. Additionally, ANCOVA and independent t-tests were used to compare both early and sustained coarse coding in subgroups of good and poor RHD comprehenders. OUTCOMES #ENTITYSTARTX00026; RESULTS: The group with RHD was less accurate than the control group on all measures. The finding of coarse coding impairment (difficulty activating/sustaining activation of a word's peripheral features) may appear to contradict prior evidence of RHD suppression deficit (prolonged activation for context-inappropriate meanings of words). However, the sentence contexts in this study were unbiased and thus did not provide an appropriate test of suppression function. Correlations between coarse coding and the discourse measures were small and nonsignificant. There were no differences in coarse coding between RHD comprehension subgroups on the high-level inferencing task. There was also no distinction in early coarse coding for subgroups based on comprehension of implied main ideas and details. But for these same subgroups, there was a difference in sustained coarse coding. Poorer RHD comprehenders of implied information from discourse were also poorer at maintaining activation for semantically distant features of concrete nouns. CONCLUSIONS: This study provides evidence of a variant of the postulated link between coarse coding and discourse comprehension in RHD. Specifically, adults with RHD who were particularly poor at sustaining activation for peripheral semantic features of nouns were also relatively poor comprehenders of implied information from narratives.

What's "right" in language comprehension: ERPs reveal right hemisphere language capabilities

Although the term "nonverbal" is often applied to the right cerebral hemisphere (RH), a growing body of work indicates that the RH can comprehend language and, indeed, that it makes critical contributions to normal language functions. Reviewed here are studies that have examined RH language capabilities by combining visual half-field presentation methods with event-related potential (ERP) measures. Because they afford temporal and functional specificity and can be obtained as participants simply process language for meaning, ERPs provide especially valuable insights into RH language functions. Such studies suggest that the RH appreciates word and message-level meaning information, and that it may play a particularly important role in the processing of relatively unpredictable semantic relationships. In addition, this work suggests that patterns observed for everyday language processing may often be an emergent property of multiple, distinct mechanisms operating in parallel as the left and right hemispheres jointly comprehend language.

The effects of context, meaning frequency, and associative strength on semantic selection: distinct contributions from each cerebral hemisphere

The visual half-field procedure was used to examine hemispheric asymmetries in meaning selection. Event-related potentials were recorded as participants decided if a lateralized ambiguous or unambiguous prime was related in meaning to a centrally presented target. Prime-target pairs were preceded by a related or unrelated centrally presented context word. To separate the effects of meaning frequency and associative strength, unambiguous words were paired with concordant weakly related context words and strongly related targets (e.g., taste-sweet-candy) that were similar in associative strength to discordant subordinate-related context words and dominant-related targets (e.g., river-bank-deposit) in the ambiguous condition. Context words and targets were reversed in a second experiment. In an unrelated (neutral) context, N400 responses were more positive than baseline (facilitated) in all ambiguous conditions except when subordinate targets were presented on left visual field-right hemisphere (LVF-RH) trials. Thus, in the absence of biasing context information, the hemispheres seem to be differentially affected by meaning frequency, with the left maintaining multiple meanings and the right selecting the dominant meaning. In the presence of discordant context information, N400 facilitation was absent in both visual fields, indicating that the contextually consistent meaning of the ambiguous word had been selected. In contrast, N400 facilitation occurred in all of the unambiguous conditions; however, the left hemisphere (LH) showed less facilitation for the weakly related target when a strongly related context was presented. These findings indicate that both hemispheres use context to guide meaning selection, but the LH is more likely to focus activation on a single, contextually relevant sense.

Lexical ambiguity in sentence comprehension

An event-related fMRI paradigm was used to investigate brain activity during the reading of sentences containing either a lexically ambiguous word or an unambiguous control word. Higher levels of activation occurred during the reading of sentences containing a lexical ambiguity. Furthermore, the activated cortical network differed, depending on: (1) whether the sentence contained a balanced (i.e., both meanings equally likely) or a biased (i.e., one meaning more likely than other meanings) ambiguous word; and, (2) the working memory capacity of the individual as assessed by reading span. The findings suggest that encountering a lexical ambiguity is dealt with by activating multiple meanings utilizing processes involving both hemispheres. When an early interpretation of a biased ambiguous word is later disambiguated to the subordinate meaning, the superior frontal cortex activates in response to the coherence break and the right inferior frontal gyrus and the insula activate, possibly to suppress the incorrect interpretation. Negative correlations between reading span scores and activation in the right hemisphere for both types of ambiguous words suggest that readers with lower spans are more likely to involve show right hemisphere involvement in the processing of the ambiguity. A positive correlation between reading span scores and insula activation appearing only for biased sentences disambiguated to the subordinate meaning indicates that individuals with higher spans were more likely to initially maintain both meanings and as a result had to suppress the unintended dominant meaning.