Semantic influences on thematic role assignment: evidence from normals and aphasics

Multimodal measures of sentence comprehension in agrammatism

Agrammatic or asyntactic comprehension is a common language impairment in aphasia. We considered three possible hypotheses about the underlying cause of this deficit, namely problems in syntactic processing, over-reliance on semantics, and a deficit in cognitive control. We tested four individuals showing asyntactic comprehension on their comprehension of syntax-semantics conflict sentences (e.g., The robber handcuffed the cop), where semantic cues pushed towards a different interpretation from syntax. Two of the four participants performed above chance on such sentences indicating that not all agrammatic individuals are impaired in structure-based interpretation. We collected additional eyetracking measures from the other two participants, who performed at chance on the conflict sentences. These measures suggested distinct underlying processing profiles in the two individuals. Cognitive assessments further suggested that one participant might have performed poorly due to a linguistic cognitive control impairment while the other had difficulty due to over-reliance on semantics. Together, the results highlight the importance of multimodal measures for teasing apart aphasic individuals' underlying deficits. They corroborate findings from neurotypical adults by showing that semantics can strongly influence comprehension and that cognitive control could be relevant for choosing between competing sentence interpretations. They extend previous findings by demonstrating variability between individuals with aphasia-cognitive control might be especially relevant for patients who are not overly reliant on semantics. Clinically, the identification of distinct underlying problems in different individuals suggests that different treatment paths might be warranted for cases who might look similar on behavioral assessments.

Parsers and Grammars: A Tutorial Overview from the Linguistics Building

The purpose of this paper is to re-examine the relationship between grammars and processing systems in light of the various forms of experimental research (especially of an electrophysiological nature) that has been conducted in the last fifteen years or so. First, the notion of 'processing strategy' or 'heuristics processing' is considered followed by a discussion of structures of great morphosyntactic complexity that parsing systems seem to tackle by simply respecting complex grammatical laws, instead of by resorting to shortcuts. Then, grammatical illusions and what these can teach us about the processing of grammar are considered. It is argued that illusions allow us to discern a few explanatory principles that may redefine the way we see parser-grammar relations. Among these is the idea that how long illusions last in the online-to-offline transition depends in part on their 'templatability', that is, the ease with which they become gestaltic templates. Another key idea is that some apparent illusions are in fact nothing more than grammar contemplated at work as in slow motion.

Agrammatic output in non-fluent, including Broca's, aphasia as a rational behavior

Background

Speech of individuals with non-fluent, including Broca's, aphasia is often characterized as "agrammatic" because their output mostly consists of nouns and, to a lesser extent, verbs and lacks function words, like articles and prepositions, and correct morphological endings. Among the earliest accounts of agrammatic output in the early 1900s was the "economy of effort" idea whereby agrammatic output is construed as a way of coping with increases in the cost of language production. This idea resurfaced in the 1980s, but in general, the field of language research has largely focused on accounts of agrammatism that postulated core deficits in syntactic knowledge.

Aims

We here revisit the economy of effort hypothesis in light of increasing emphasis in cognitive science on rational and efficient behavior.

Main contribution

The critical idea is as follows: there is a cost per unit of linguistic output, and this cost is greater for patients with non-fluent aphasia. For a rational agent, this increase leads to shorter messages. Critically, the informative parts of the message should be preserved and the redundant ones (like the function words and inflectional markers) should be omitted. Although economy of effort is unlikely to provide a unifying account of agrammatic output in all patients-the relevant population is too heterogeneous and the empirical landscape too complex for any single-factor explanation-we argue that the idea of agrammatic output as a rational behavior was dismissed prematurely and appears to provide a plausible explanation for a large subset of the reported cases of expressive aphasia.

Conclusions

The rational account of expressive agrammatism should be evaluated more carefully and systematically. On the basic research side, pursuing this hypothesis may reveal how the human mind and brain optimize communicative efficiency in the presence of production difficulties. And on the applied side, this construal of expressive agrammatism emphasizes the strengths of some patients to flexibly adapt utterances in order to communicate in spite of grammatical difficulties; and focusing on these strengths may be more effective than trying to "fix" their grammar.

Comprehension of Vernacular Features in Aphasia

PURPOSE

Insights from linguistic variation research illustrate a linguistically diverse population, in which even speakers who can be classified as speaking a "mainstream" variety have grammatical knowledge of vernacular or "nonmainstream" features. However, there is a gap in our knowledge regarding how vernacular features are comprehended in people with aphasia (PWA). This article presents the results of a pilot study exploring how PWA respond to linguistic stimuli that include the vernacular feature, negative concord (NC), often referred to by the more colloquial term double negative (e.g., I didn't do nothing, equivalent to I didn't do anything).

METHOD

Twelve PWA in the chronic stage of recovery each rated the naturalness and felicity of 48 critical sentences and 64 fillers, all of which contained two clauses, the second clause describing a consequence of the first. Ratings were analyzed using ordinal regression.

RESULTS

PWA rated NC sentences as unacceptable, but felicitous-a pattern similar to that shown by neurologically intact adults in a previous study.

CONCLUSIONS

These results suggest that PWA are sensitive to both social and linguistic information at levels similar to neurologically intact speakers. These results have implications for the integration of vernacular features into future research, assessment, and treatment protocols for PWA.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.19027322.

Evidence for the Concreteness of Abstract Language: A Meta-Analysis of Neuroimaging Studies

The neural mechanisms subserving the processing of abstract concepts remain largely debated. Even within the embodiment theoretical framework, most authors suggest that abstract concepts are coded in a linguistic propositional format, although they do not completely deny the role of sensorimotor and emotional experiences in coding it. To our knowledge, only one recent proposal puts forward that the processing of concrete and abstract concepts relies on the same mechanisms, with the only difference being in the complexity of the underlying experiences. In this paper, we performed a meta-analysis using the Activation Likelihood Estimates (ALE) method on 33 functional neuroimaging studies that considered activations related to abstract and concrete concepts. The results suggest that (1) concrete and abstract concepts share the recruitment of the temporo-fronto-parietal circuits normally involved in the interactions with the physical world, (2) processing concrete concepts recruits fronto-parietal areas better than abstract concepts, and (3) abstract concepts recruit Broca's region more strongly than concrete ones. Based on anatomical and physiological evidence, Broca's region is not only a linguistic region mainly devoted to speech production, but it is endowed with complex motor representations of different biological effectors. Hence, we propose that the stronger recruitment of this region for abstract concepts is expression of the complex sensorimotor experiences underlying it, rather than evidence of a purely linguistic format of its processing.

Semantic memory for objects, actions, and events: A novel test of event-related conceptual semantic knowledge

People possess significant knowledge about how real-world events typically unfold. Such event-related semantic memory connects action and object knowledge, is essential for multiple stages of language processing, and may be impaired in neurological conditions like aphasia. However, current assessments are not well designed for measuring this knowledge. This study presents and tests a novel measure of event-related semantic memory. Task-performance data were collected from unimpaired adults across the lifespan and a sample of stroke survivors with aphasia. Individuals with aphasia also completed measures of language processing and action-/object-related semantic memory, to establish the novel measure's convergent validity. Results demonstrate that performance on the event-knowledge measure correlated with action and object semantic-memory measures and was also associated with a broader range of language-processing performance than other semantic-memory measures. These findings suggest that the novel measure can be used to detect the presence and impact of event-knowledge impairments in neurological conditions.

Electrophysiology of prosodic and lexical-semantic processing during sentence comprehension in aphasia

Event-related potentials (ERPs) were used to examine how individuals with aphasia and a group of age-matched controls use prosody and themattic fit information in sentences containing temporary syntactic ambiguities. Two groups of individuals with aphasia were investigated; those demonstrating relatively good sentence comprehension whose primary language difficulty is anomia (Individuals with Anomic Aphasia (IWAA)), and those who demonstrate impaired sentence comprehension whose primary diagnosis is Broca's aphasia (Individuals with Broca's Aphasia (IWBA)). The stimuli had early closure syntactic structure and contained a temporary early closure (correct)/late closure (incorrect) syntactic ambiguity. The prosody was manipulated to either be congruent or incongruent, and the temporarily ambiguous NP was also manipulated to either be a plausible or an implausible continuation for the subordinate verb (e.g., "While the band played the song/the beer pleased all the customers."). It was hypothesized that an implausible NP in sentences with incongruent prosody may provide the parser with a plausibility cue that could be used to predict syntactic structure. The results revealed that incongruent prosody paired with a plausibility cue resulted in an N400-P600 complex at the implausible NP (the beer) in both the controls and the IWAAs, yet incongruent prosody without a plausibility cue resulted in an N400-P600 at the critical verb (pleased) only in healthy controls. IWBAs did not show evidence of N400 or P600 effects at the ambiguous NP or critical verb, although they did show evidence of a delayed N400 effect at the sentence-final word in sentences with incongruent prosody. These results suggest that IWAAs have difficulty integrating prosodic cues with underlying syntactic structure when lexical-semantic information is not available to aid their parse. IWBAs have difficulty integrating both prosodic and lexical-semantic cues with syntactic structure, likely due to a processing delay.

"Whatdunit?" Sentence Comprehension Abilities of Children With SLI: Sensitivity to Word Order in Canonical and Noncanonical Structures

PURPOSE

With Aim 1, we compared the comprehension of and sensitivity to canonical and noncanonical word order structures in school-age children with specific language impairment (SLI) and same-age typically developing (TD) children. Aim 2 centered on the developmental improvement of sentence comprehension in the groups. With Aim 3, we compared the comprehension error patterns of the groups.

METHOD

Using a "Whatdunit" agent selection task, 117 children with SLI and 117 TD children (ages 7:0-11:11, years:months) propensity matched on age, gender, mother's education, and family income pointed to the picture that best represented the agent in semantically implausible canonical structures (subject-verb-object, subject relative) and noncanonical structures (passive, object relative).

RESULTS

The SLI group performed worse than the TD group across sentence types. TD children demonstrated developmental improvement across each sentence type, but children with SLI showed improvement only for canonical sentences. Both groups chose the object noun as agent significantly more often than the noun appearing in a prepositional phrase.

CONCLUSIONS

In the absence of semantic-pragmatic cues, comprehension of canonical and noncanonical sentences by children with SLI is limited, with noncanonical sentence comprehension being disproportionately limited. The children's ability to make proper semantic role assignments to the noun arguments in sentences, especially noncanonical, is significantly hindered.

A rational inference approach to group and individual-level sentence comprehension performance in aphasia

The rational inference, or noisy channel, account of language comprehension predicts that comprehenders are sensitive to the probabilities of different interpretations for a given sentence and adapt as these probabilities change (Gibson, Bergen & Piantadosi, 2013). This account provides an important new perspective on aphasic sentence comprehension: aphasia may increase the likelihood of sentence distortion, leading people with aphasia (PWA) to rely more on the prior probability of an interpretation and less on the form or structure of the sentence (Gibson, Sandberg, Fedorenko, Bergen & Kiran, 2015). We report the results of a sentence-picture matching experiment that tested the predictions of the rational inference account and other current models of aphasic sentence comprehension across a variety of sentence structures. Consistent with the rational inference account, PWA showed similar sensitivity to the probability of particular kinds of form distortions as age-matched controls, yet overall their interpretations relied more on prior probability and less on sentence form. As predicted by rational inference, but not by other models of sentence comprehension in aphasia, PWA's interpretations were more faithful to the form for active and passive sentences than for direct object and prepositional object sentences. However contra rational inference, there was no evidence that individual PWA's severity of syntactic or semantic impairment predicted their sensitivity to form versus the prior probability of a sentence, as cued by semantics. These findings confirm and extend previous findings that suggest the rational inference account holds promise for explaining aphasic and neurotypical comprehension, but they also raise new challenges for the account.

Identifying thematic roles from neural representations measured by functional magnetic resonance imaging

The generativity and complexity of human thought stem in large part from the ability to represent relations among concepts and form propositions. The current study reveals how a given object such as rabbit is neurally encoded differently and identifiably depending on whether it is an agent ("the rabbit punches the monkey") or a patient ("the monkey punches the rabbit"). Machine-learning classifiers were trained on functional magnetic resonance imaging (fMRI) data evoked by a set of short videos that conveyed agent-verb-patient propositions. When tested on a held-out video, the classifiers were able to reliably identify the thematic role of an object from its associated fMRI activation pattern. Moreover, when trained on one subset of the study participants, classifiers reliably identified the thematic roles in the data of a left-out participant (mean accuracy = .66), indicating that the neural representations of thematic roles were common across individuals.

How to constrain and maintain a lexicon for the treatment of progressive semantic naming deficits: Principles of item selection for formal semantic therapy

The progressive degradation of semantic memory is a common feature of many forms of dementia, including Alzheimer's disease and the semantic variant of primary progressive aphasia (svPPA). One of the most functionally debilitating effects of this semantic impairment is the inability to name common people and objects (i.e., anomia). Clinical management of a progressive, semantically based anomia presents extraordinary challenges for neurorehabilitation. Techniques such as errorless learning and spaced-retrieval training show promise for retraining forgotten words. However, we lack complementary detail about what to train (i.e., item selection) and how to flexibly adapt the training to a declining cognitive system. This position paper weighs the relative merits of several treatment rationales (e.g., restore vs. compensate) and advocates for maintenance of known words over reacquisition of forgotten knowledge in the context of semantic treatment paradigms. I propose a system for generating an item pool and outline a set of core principles for training and sustaining a micro-lexicon consisting of approximately 100 words. These principles are informed by lessons learned over the course of a Phase I treatment study targeting language maintenance over a 5-year span in Alzheimer's disease and SvPPA. Finally, I propose a semantic training approach that capitalises on lexical frequency and repeated training on conceptual structure to offset the loss of key vocabulary as disease severity worsens.

Animacy and competition in relative clause production: a cross-linguistic investigation

This work investigates production preferences in different languages. Specifically, it examines how animacy, competition processes, and language-specific constraints shape speakers' choices of structure. English, Spanish and Serbian speakers were presented with depicted events in which either an animate or inanimate entity was acted upon by an agent. Questions about the affected participant in these events prompted the production of relative clauses identifying these entities (e.g., the bag the woman is punching). Results indicated that in English, animacy plays a strong role in determining the choice of passive structures. In contrast, it plays a less prominent role in Spanish and Serbian structure choices, where more active structures were produced to varying degrees. Critically, the semantic similarity between the agent and the patient of the event correlated with the omission of the agent in all languages, indicating that competition resulted in the agent's inhibition. Similarity also correlated with different functional choices in Spanish. The results suggest that similarity-based competition may influence various stages of production planning but its manifestations are constrained by language-specific grammatical options. Implications for models of sentence production and the relationship between production and comprehension are discussed.

BOLD response to semantic and syntactic processing during hypoglycemia is load-dependent

This study investigates how syntactic and semantic load factors impact sentence comprehension and BOLD signal under moderate hypoglycemia. A dual session, whole brain fMRI study was conducted on 16 healthy participants using the glucose clamp technique. In one session, they experienced insulin-induced hypoglycemia (plasma glucose at ∼50mg/dL); in the other, plasma glucose was maintained at euglycemic levels (∼100mg/dL). During scans subjects were presented with sentences of contrasting syntactic (embedding vs. conjunction) and semantic (reversibility vs. irreversibility) load. Semantic factors dominated the overall load effects on both performance (p<0.001) and BOLD response (p<0.01, corrected). Differential BOLD signal was observed in frontal, temporal, temporo-parietal and medio-temporal regions. Hypoglycemia and syntactic factors significantly impacted performance (p=0.002) and BOLD response (p<0.01, corrected) in the reversible clause conditions, more extensively in reversible-embedded than in reversible-conjoined clauses. Hypoglycemia resulted in a robust decrease in performance on reversible clauses and exerted attenuating effects on BOLD unselectively across cortical circuits. The dominance of reversibility in all measures underscores the distinction between the syntactic and semantic contrasts. The syntactic is based in a quantitative difference in algorithms interpreting embedded and conjoined structures. We suggest that the semantic is based in a qualitative difference between algorithmic mapping of arguments in reversible clauses and heuristic linking in irreversible clauses. Because heuristics drastically reduce resource demand, the operations they support would resist the load-dependent cognitive consequences of hypoglycemia.

Attention, working memory, and grammaticality judgment in typical young adults

PURPOSE

To examine resource allocation and sentence processing, this study examined the effects of auditory distraction on grammaticality judgment (GJ) of sentences varied by semantics (reversibility) and short-term memory requirements.

METHOD

Experiment 1: Typical young adult females (N = 60) completed a whole-sentence GJ task in distraction (Quiet, Noise, or Talk). Participants judged grammaticality of Passive sentences varied by sentence (length), grammaticality, and reversibility. Reaction time (RT) data were analyzed using a mixed analysis of variance. Experiment 2: A similar group completed a self-paced reading GJ task using the similar materials.

RESULTS

Experiment 1: Participants responded faster to Bad and to Nonreversible sentences, and in the Talk distraction. The slowest RTs were noted for Good-Reversible-Padded sentences in the Quiet condition. Experiment 2: Distraction did not differentially affect RTs for sentence components. Verb RTs were slower for Reversible sentences.

CONCLUSIONS

Results suggest that narrative distraction affected GJ, but by speeding responses, not slowing them. Sentence variables of memory and reversibility slowed RTs, but narrative distraction resulted in faster processing times regardless of individual sentence variables. More explicit, deliberate tasks (self-paced reading) resulted in less effect from distraction. Results are discussed in terms of recent theories about auditory distraction.

The influence of mood on the processing of syntactic anomalies: evidence from P600

In several domains of psychology it has been shown that mood influences the way in which we process information. So far, little is known about the relation between mood and processes of language comprehension. In the present study we explore, whether, and if so how, mood affects the processing of syntactic anomalies in real time by recording event-related potentials (ERPs). To this aim we compared the P600 effect to subject-verb agreement errors relative to correct sentences while ERPs were recorded and mood was manipulated by presenting happy or sad film clips. The prediction was that if emotional state affects processes of language comprehension this should be reflected by an interaction between mood and P600. The results were as follows: first, the mood induction procedure was effective: participants were happier after watching happy film clips and sadder after watching sad film clips compared to baseline. Second, for P600 a mood by syntactic correctness interaction was obtained for the midline and lateral electrodes. The interaction reflected a broadly distributed P600 effect for the happy mood condition and a strong reduction in P600 effect for the sad mood condition. Correlation analyses confirmed that the observed changes in P600 effect were accompanied by reliable changes in emotional state. The present ERP findings demonstrate that mood interacts with processes of language comprehension. Three possible explanations for the mood by syntactic correctness interaction are discussed; one in terms of syntactic processing, one in terms of heuristic processing, and one in terms of more general factors like attention and/or motivation.

Neuronal activation for semantically reversible sentences

Semantically reversible sentences are prone to misinterpretation and take longer for typically developing children and adults to comprehend; they are also particularly problematic for those with language difficulties such as aphasia or Specific Language Impairment. In our study, we used fMRI to compare the processing of semantically reversible and nonreversible sentences in 41 healthy participants to identify how semantic reversibility influences neuronal activation. By including several linguistic and nonlinguistic conditions within our paradigm, we were also able to test whether the processing of semantically reversible sentences places additional load on sentence-specific processing, such as syntactic processing and syntactic-semantic integration, or on phonological working memory. Our results identified increased activation for reversible sentences in a region on the left temporal-parietal boundary, which was also activated when the same group of participants carried out an articulation task which involved saying "one, three" repeatedly. We conclude that the processing of semantically reversible sentences places additional demands on the subarticulation component of phonological working memory.

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

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

Knowing where but not what: impaired thematic roles and spatial language

We describe case J.P. who, following a left inferior frontal lesion, made frequent role confusions in comprehension and production (e.g., saying "The boy kicks the girl" for a picture showing a girl kicking a boy). J.P.'s preserved ability to judge the grammaticality of sentences rules out a syntactic deficit as the primary cause of the role confusions. Thematic role assignment is also required with spatial prepositions such as in or above, and J.P.'s thematic role assignment was also severely impaired with spatial prepositions. We capitalized on prior linguistic analyses and behavioural studies to design accurate tests of the semantics of spatial terms, spatial relations, and critical features of objects. Fine-grain semantic tests revealed that the semantics of spatial terms and objects was intact. We hypothesize that J.P.'s role confusions reflected a failure to integrate objects within semantic representations that define the thematic roles. Our data suggest that properties of objects and thematic roles are specified by distinct semantic processes, which have different brain localizations. J.P.'s lesion further suggests that left inferior frontal regions are critical in thematic role assignment, thus contributing to the understanding of the linguistic functions of these regions.

The interplay of heuristics and parsing routines in sentence comprehension: Evidence from ERPs and reaction times

Semantic anomalies like "the fox that hunted the poacher" elicit P600 effects. Kolk et al. [Kolk, H.J., Chwilla, D.J., Van Herten, M., Oor, P.J.W., 2003. Structure and limited capacity in verbal working memory: a study with event related potentials. Brain and language, 85(1), 1-36] proposed that this P600 effect is triggered by a conflict between the outcome of a lexical strategy with that of the parsing routine. Specifically, when the lexical strategy indicates that the poacher hunted the fox, the full parse leads to the conclusion that the fox was the one who did the hunting. We tested this hypothesis by replicating the study cited above but manipulating the context by means of instruction. Participants were informed that semantic anomalies were created on purpose and that they should not be misled by these anomalies but instead focus on syntax or sentence structure. This instruction led to a strong reduction in P600 effect. This result supports the view that expectations play an important role in the generation of P600 effects to semantic anomalies, as proposed by Kolk et al. [Kolk, H.J., Chwilla, D.J., Van Herten, M., Oor, P.J.W., 2003. Structure and limited capacity in verbal working memory: a study with event related potentials. Brain and language, 85(1), 1-36].

Thematic role assignment in patients with Broca's aphasia: Sentence–picture matching electrified

An event-related brain potential experiment was carried out to investigate on-line thematic role assignment during sentence-picture matching in patients with Broca's aphasia. Subjects were presented with a picture that was followed by an auditory sentence. The sentence either matched the picture or mismatched the visual information depicted. Sentences differed in complexity, and ranged from simple active semantically irreversible sentences to passive semantically reversible sentences. ERPs were recorded while subjects were engaged in sentence-picture matching. In addition, reaction time and accuracy were measured. Three groups of subjects were tested: Broca patients (N=10), non-aphasic patients with a right hemisphere (RH) lesion (N=8), and healthy aged-matched controls (N=15). The results of this study showed that, in neurologically unimpaired individuals, thematic role assignment in the context of visual information was an immediate process. This in contrast to patients with Broca's aphasia who demonstrated no signs of on-line sensitivity to the picture-sentence mismatches. The syntactic contribution to the thematic role assignment process seemed to be diminished given the reduction and even absence of P600 effects. Nevertheless, Broca patients showed some off-line behavioral sensitivity to the sentence-picture mismatches. The long response latencies of Broca's aphasics make it likely that off-line response strategies were used.

Neural mechanisms of language comprehension: challenges to syntax

In 1980, the N400 event-related potential was described in association with semantic anomalies within sentences. When, in 1992, a second waveform, the P600, was reported in association with syntactic anomalies and ambiguities, the story appeared to be complete: the brain respected a distinction between semantic and syntactic representation and processes. Subsequent studies showed that the P600 to syntactic anomalies and ambiguities was modulated by lexical and discourse factors. Most surprisingly, more than a decade after the P600 was first described, a series of studies reported that semantic verb-argument violations, in the absence of any violations or ambiguities of syntax can evoke robust P600 effects and no N400 effects. These observations have raised fundamental questions about the relationship between semantic and syntactic processing in the brain. This paper provides a comprehensive review of the recent studies that have demonstrated P600s to semantic violations in light of several proposed triggers: semantic-thematic attraction, semantic associative relationships, animacy and semantic-thematic violations, plausibility, task, and context. I then discuss these findings in relation to a unifying theory that attempts to bring some of these factors together and to link the P600 produced by semantic verb-argument violations with the P600 evoked by unambiguous syntactic violations and syntactic ambiguities. I suggest that normal language comprehension proceeds along at least two competing neural processing streams: a semantic memory-based mechanism, and a combinatorial mechanism (or mechanisms) that assigns structure to a sentence primarily on the basis of morphosyntactic rules, but also on the basis of certain semantic-thematic constraints. I suggest that conflicts between the different representations that are output by these distinct but interactive streams lead to a continued combinatorial analysis that is reflected by the P600 effect. I discuss some of the implications of this non-syntactocentric, dynamic model of language processing for understanding individual differences, language processing disorders and the neuroanatomical circuitry engaged during language comprehension. Finally, I suggest that that these two processing streams may generalize beyond the language system to real-world visual event comprehension.

The frontal lobes and the regulation of mental activity

Results of neuroimaging and neuropsychological studies of frontal lobe function have been interpreted by some as evidence for specialized modules that are localized to distinct regions of frontal cortex, and that differ in both content and process from those in neighboring regions. These descriptions stand in stark contrast to the many domain-general theoretical accounts of the regulatory role of the frontal lobes in cognition. Recent attempts to understand how general regulatory mechanisms might operate across multiple domains (e.g. working memory, sentence comprehension) have been increasingly important in our understanding of the frontal lobes.

Retrieval of abstract semantics

Behavioural and neuropsychological evidence suggests that abstract and concrete concepts might be represented, retrieved and processed differently in the human brain. Using fMRI, we demonstrate that retrieval of abstract relative to sensory-based semantics during synonym judgements increased activation in a left frontotemporal system that has been associated with semantic processing particularly at the sentence level. Since activation increases were observed irrespective of the degree of difficulty, we suggest that these differential activations might reflect a particular retrieval mechanism or strategy for abstract concepts. In contrast to sensory-based semantics, the meaning of abstract concepts is largely specified by their usage in language rather than by their relations to the physical world. Subjects might therefore generate an appropriate semantic sentential context to fully explore and specify the meaning of abstract concepts. Our results also explain why abstract semantics is vulnerable to left frontotemporal lesions.

Simulation of aphasic naming performance in non-brain-damaged adults

Discussion abounds in the literature as to whether aphasia is a deficit of linguistic competence or linguistic performance and, if it is a performance deficit, what are its precise mechanisms. Considerable evidence suggests that alteration of nonlinguistic factors can affect language performance in aphasia, a finding that raises questions about the modularity of language and the purity of linguistic mechanisms underlying the putative language deficits in persons with aphasia. This study investigated whether temporal stress plus additional cognitive demands placed on non-brain-damaged adults would produce aphasic-like performance on a picture naming task. Two groups of non-brain-damaged participants completed a picture naming task with additional cognitive demands (use of low frequency words and making semantic judgments about the stimuli). A control group performed this task at their own pace, and an experimental group was placed under time constraints. Naming errors were identified and coded by error type. Errors made by individuals with aphasia from a previous study (S. E. Kohn and H. Goodglass, 1985) were recoded with the coding system used in the present study and were then compared with the types of errors produced by the 2 non-brain-damaged groups. Results generally support the hypothesis that the language performance deficits seen in persons with aphasia exist on a continuum with the language performance of non-brain-damaged individuals. Some error type differences between groups warrant further investigation.

Language processing: functional organization and neuroanatomical basis

Earlier formulations of the relation of language and the brain provided oversimplified accounts of the nature of language disorders, classifying patients into syndromes characterized by the disruption of sensory or motor word representations or by the disruption of syntax or semantics. More recent neuropsychological findings, drawn mainly from case studies, provide evidence regarding the various levels of representations and processes involved in single-word and sentence processing. Lesion data and neuroimaging findings are converging to some extent in providing localization of these components of language processing, particularly at the single-word level. Much work remains to be done in developing precise theoretical accounts of sentence processing that can accommodate the observed patterns of breakdown. Such theoretical developments may provide a means of accommodating the seemingly contradictory findings regarding the neural organization of sentence processing.

Structure and limited capacity in verbal working memory: a study with event-related potentials

In order to test recent claims about the structure of verbal working memory, two ERP experiments with Dutch speaking participants were carried out. We compared the ERP effects of syntactic and semantic mid-sentence anomalies in subject and object relative sentences. In Experiment 1, the participants made acceptability judgments, while in Experiment 2 they read for comprehension. Syntactic anomalies concerned subject-verb disagreement, while semantic anomalies were related to implausible events (e.g., *The cat that fled from the mice ran through the room). Semantic anomalies did not elicit an N400 effect. The semantic as well as syntactic anomalies elicited P600 effects, with similar centro-parietal scalp distributions. For both kinds of anomaly, the P600 effects were modulated by syntactic complexity: they were either relatively small (Experiment 1) or absent (Experiment 2) in object relative sentences. Taken together, our results suggest that: (a) verbal working memory is a limited capacity system; (b) it is not subdivided into an interpretative and a post-interpretative component (); (c) the P600 can reflect the presence of a semantic bias in syntactically unambiguous sentences; (d) the P600 is related to language monitoring: its function is to check upon the veridicality of an unexpected (linguistic) event; (e) if such a check is made, there is no integration of the event and hence no N400 effect.

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

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

Remediation of asyntactic sentence comprehension using a multimedia microworld

We report the evaluation of a new automated protocol for the treatment of asyntactic comprehension. This is a follow-up study to the "Microworld for Aphasia" work of Crerer, Ellis, and Dean (1996). An efficacy study involving three patients is reported. All three patients achieved statistically significant improvements in written sentence comprehension as a result of eight hours of treatment focusing on active, passive, and object cleft sentence structures. Treatment effects generalized both to untreated Microworld sentences and to the more naturalistic sentences of the Philadelphia Comprehension Battery (Saffran, Schwartz, Linebarger, Martin, & Bochetto, 1988), with some further evidence of generalization to spoken sentence comprehension. Treatment effects were obtained with minimal input from a clinician.

Adaptive learning: interventions for verbal and motor deficits

Advances in basic and clinical neuroscience are uniting to form new optimism for treatment and rehabilitation of persons with a variety of neurologic disorders. Both cognitive and motor systems have shown remarkable degrees of plasticity in response to incoming stimuli. Understanding the brain (and spinal cord) capacity for change will lead to new topics for research as well as new approaches to rehabilitation. Adaptive learning has been shown to be a fundamental part of the developmental process and has been used in remediation of a variety of language difficulties. Using such principles to approach motor functions also is showing promise. Expanding these observations to encompass other areas of disease and rehabilitation is an area for further research. Interdisciplinary approaches including the fields of computer technology, imaging, and genetic analysis will provide new tools. Contribution of new concepts within adaptive learning must address such topics as the relation between motor and sensory responses, measures that accurately indicate cognitive health, the brain and spinal cord areas involved in particular learning tasks, the optimal time windows for intervention, and the importance of behavior and motivation in treatment and rehabilitation.