Malathi Thothathiri

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.

The neural basis of reversible sentence comprehension: Evidence from voxel-based lesion symptom mapping in aphasia

We explored the neural basis of reversible sentence comprehension in a large group of aphasic patients (n = 79). Voxel-based lesion symptom mapping revealed a significant association between damage in temporo-parietal cortex and impaired sentence comprehension. This association remained after we controlled for phonological working memory. We hypothesize that this region plays an important role in the thematic or what–where processing of sentences. In contrast, we detected weak or no association between reversible sentence comprehension and the ventrolateral pFC, which includes Brocas area, even for syntactically complex sentences. This casts doubt on theories that presuppose a critical role for this region in syntactic computations.

Parametric effects of syntactic–semantic conflict in Broca’s area during sentence processing

The hypothesized role of Brocas area in sentence processing ranges from domain-general executive function to domain-specific computation that is specific to certain syntactic structures. We examined this issue by manipulating syntactic structure and conflict between syntactic and semantic cues in a sentence processing task. Functional neuroimaging revealed that activation within several Brocas area regions of interest reflected the parametric variation in syntactic-semantic conflict. These results suggest that Brocas area supports sentence processing by mediating between multiple incompatible constraints on sentence interpretation, consistent with this areas well-known role in conflict resolution in other linguistic and non-linguistic tasks.

Cognitive control during sentence generation

ABSTRACT Sentence generation involves selecting the right words out of multiple co-activated representations for the right utterance positions. This selection process is hypothesized to involve cognitive control. Previous research has linked cognitive control during language processing to regions within the frontal lobe, including the anterior cingulate cortex (ACC) and left ventrolateral prefrontal cortex (VLPFC). We examined the neural correlates of word and sentence generation to determine whether these cognitive control regions were activated more for sentences than words. We also manipulated the phonological overlap between nouns in the sentence to determine whether cognitive control recruitment increased under phonological competition. Whole-brain analysis revealed increased activation in the ACC and bilateral frontal cortex for sentences over words. Region of interest analysis revealed an effect of phonological competition within the ACC. Psychophysiological interaction (PPI) analysis further showed that functional connectivity within a task-maintenance network increased under phonological competition. These results suggest a role for conflict detection and monitoring during sentence generation, which is consistent with a theoretical framework incorporating domain-general cognitive control processes into language processing.

Acquiring and Producing Sentences: Whether Learners Use Verb-Specific or Verb-General Information Depends on Cue Validity

Learning to produce sentences involves learning patterns that enable the generation of new utterances. Language contains both verb-specific and verb-general regularities that are relevant to this capacity. Previous research has focused on whether one source is more important than the other. We tested whether the production system can flexibly learn to use either source, depending on the predictive validity of different cues in the input. Participants learned new sentence structures in a miniature language paradigm. In three experiments, we manipulated whether individual verbs or verb-general mappings better predicted the structures heard during learning. Evaluation of participants’ subsequent production revealed that they could use either the structural preferences of individual verbs or abstract meaning-to-form mappings to construct new sentences. Further, this choice varied according to cue validity. These results demonstrate flexibility within the production architecture and the importance of considering how language was learned when discussing how language is used.

Ventral and dorsal streams for choosing word order during sentence production

Significance Languages allow multiple word orders for expressing the same meaning. Prior statistical experience with verbs in less-common sentence structures is known to facilitate subsequent use of those structures. To investigate how this is implemented in the brain, we trained participants in an artificial language and examined how they used that language to describe novel scenarios. Different verbs were associated with different word orders during training. Functional activation and connectivity patterns revealed that the choice of word order was supported by a ventral pathway for verbs that appeared in two competing orders, and dorsal pathways for verbs that appeared exclusively in the less-common order. Thus, the brain accomplishes the same language output via different routes, depending on past experience. Proficient language use requires speakers to vary word order and choose between different ways of expressing the same meaning. Prior statistical associations between individual verbs and different word orders are known to influence speakers’ choices, but the underlying neural mechanisms are unknown. Here we show that distinct neural pathways are used for verbs with different statistical associations. We manipulated statistical experience by training participants in a language containing novel verbs and two alternative word orders (agent-before-patient, AP; patient-before-agent, PA). Some verbs appeared exclusively in AP, others exclusively in PA, and yet others in both orders. Subsequently, we used sparse sampling neuroimaging to examine the neural substrates as participants generated new sentences in the scanner. Behaviorally, participants showed an overall preference for AP order, but also increased PA order for verbs experienced in that order, reflecting statistical learning. Functional activation and connectivity analyses revealed distinct networks underlying the increased PA production. Verbs experienced in both orders during training preferentially recruited a ventral stream, indicating the use of conceptual processing for mapping meaning to word order. In contrast, verbs experienced solely in PA order recruited dorsal pathways, indicating the use of selective attention and sensorimotor integration for choosing words in the right order. These results show that the brain tracks the structural associations of individual verbs and that the same structural output may be achieved via ventral or dorsal streams, depending on the type of regularities in the input.

Verb bias and verb-specific competition effects on sentence production

How do speakers choose between structural options for expressing a given meaning? Overall preference for some structures over others as well as prior statistical association between specific verbs and sentence structures (“verb bias”) are known to broadly influence language use. However, the effects of prior statistical experience on the planning and execution of utterances and the mechanisms that facilitate structural choice for verbs with different biases have not been fully explored. In this study, we manipulated verb bias for English double-object (DO) and prepositional-object (PO) dative structures: some verbs appeared solely in the DO structure (DO-only), others solely in PO (PO-only) and yet others equally in both (Equi). Structural choices during subsequent free-choice sentence production revealed the expected dispreference for DO overall but critically also a reliable linear trend in DO production that was consistent with verb bias (DO-only > Equi > PO-only). Going beyond the general verb bias effect, three results suggested that Equi verbs, which were associated equally with the two structures, engendered verb-specific competition and required additional resources for choosing the dispreferred DO structure. First, DO production with Equi verbs but not the other verbs correlated with participants’ inhibition ability. Second, utterance duration prior to the choice of a DO structure showed a quadratic trend (DO-only < Equi > PO-only) with the longest durations for Equi verbs. Third, eye movements consistent with reimagining the event also showed a quadratic trend (DO-only < Equi > PO-only) prior to choosing DO, suggesting that participants used such recall particularly for Equi verbs. Together, these analyses of structural choices, utterance durations, eye movements and individual differences in executive functions shed light on the effects of verb bias and verb-specific competition on sentence production and the role of different executive functions in choosing between sentence structures.

Who did what? A causal role for cognitive control in thematic role assignment during sentence comprehension

Thematic role assignment - generally, figuring out who did what to whom - is a critical component of sentence comprehension, which is influenced by both syntactic and semantic cues. Conflict between these cues can result in temporary consideration of multiple incompatible interpretations during real-time sentence processing. We tested whether the resolution of syntax-semantics conflict can be expedited by the online engagement of cognitive control processes that are routinely used to regulate behavior across domains. In this study, cognitive control deployment from a previous Stroop trial influenced eye movements during subsequent sentence comprehension. Specifically, when syntactic and semantic cues competed for influence on interpretation, dynamic cognitive control engagement led to (a) fewer overall looks to a picture illustrating the competing but incorrect interpretation (Experiment 1), or (b) steeper growth in looks to a picture illustrating the correct interpretation (Experiment 2). Thus, prior cognitive control engagement facilitated the resolution of syntax-semantics conflict by biasing processing towards the intended analysis. This conflict adaptation effect demonstrates a causal connection between cognitive control and real-time thematic role assignment. Broader patterns demonstrated that prior cognitive control engagement also modulated sentence processing irrespective of the presence of conflict, reflecting increased integration of newly arriving cues with prior sentential content. Together, the results suggest that cognitive control helps listeners determine correct event roles during real-time comprehension.

Statistical experience and individual cognitive differences modulate neural activity during sentence production

HighlightsStatistical experience was manipulated in lab‐based training.Individual differences in conflict control were measured using Stroop.Neural activity during sentence production varied between individuals.Verbs with different statistical properties showed different activation patterns.Neural architecture for sentence production is flexible, not fixed. ABSTRACT I explored how individual cognitive differences combine with prior statistical experience to determine choice of sentence structure during speech. Participants were exposed to English language input with controlled statistical properties wherein some verbs appeared equally often in two possible structures and others appeared in only one. Subsequently, they produced sentences naturally while their brain activity was scanned. Choosing a less preferred over a more preferred structure recruited regions involved in conflict control, especially in individuals with better control abilities. Activity within a key region, the anterior cingulate cortex or ACC, varied parametrically with the statistical input properties. ACC activation showed different correlations with language production and different functional connectivity patterns for different verbs. These results demonstrate how the adult brain adjusts to ongoing language experience and recruits different neural resources to accomplish the same speech goal under different circumstances.

The relationship between short-term memory, conflict resolution, and sentence comprehension impairments in aphasia

ABSTRACT Background: Sentence comprehension involves the integration of multiple linguistic representations. This integration can be especially challenging when different cues lead to conflicting interpretations. Short-term memory (STM) and conflict resolution are two processes that have been previously linked to sentence comprehension and could assist in integration. However, the relation of each process to comprehension independently of the other has not been fully clarified. Aims: We tested two patients with contrasting STM and conflict resolution profiles in different sentence comprehension tasks to evaluate the relationship between the three abilities. Methods & Procedures: Patients completed (a) six STM tasks that tested either span or updating; (b) two executive function tasks that tested conflict resolution; and (c) three tasks that evaluated sentence comprehension. Outcomes & Results: The patient with poorer STM and better conflict resolution had variable success in sentence comprehension that was contingent on memory load and the extent to which interpretation was supported by semantic knowledge. In contrast, the patient with good STM but slow conflict resolution demonstrated accurate comprehension across all tasks and conditions, and delayed reaction times for sentences containing conflict between cues. Conclusions: The results provide broad support for a link between STM and sentence comprehension. They suggest that inefficient conflict resolution might be associated with slowed down but not inaccurate comprehension of sentences when other abilities, including STM, are intact. We discuss the ways in which STM and conflict resolution may and may not assist sentence comprehension in individuals with aphasia.