In search of on-line locality effects in sentence comprehension

Many comprehension theories assert that increasing the distance between elements participating in a linguistic relation (e.g., a verb and a noun phrase argument) increases the difficulty of establishing that relation during on-line comprehension. Such locality effects are expected to increase reading times and are thought to reveal properties and limitations of the short-term memory system that supports comprehension. Despite their theoretical importance and putative ubiquity, however, evidence for on-line locality effects is quite narrow linguistically and methodologically: It is restricted almost exclusively to self-paced reading of complex structures involving a particular class of syntactic relation. We present 4 experiments (2 self-paced reading and 2 eyetracking experiments) that demonstrate locality effects in the course of establishing subject-verb dependencies; locality effects are seen even in materials that can be read quickly and easily. These locality effects are observable in the earliest possible eye-movement measures and are of much shorter duration than previously reported effects. To account for the observed empirical patterns, we outline a processing model of the adaptive control of button pressing and eye movements. This model makes progress toward the goal of eliminating linking assumptions between memory constructs and empirical measures in favor of explicit theories of the coordinated control of motor responses and parsing.     

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

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

The dynamic influence of emotional words on sentence comprehension: An ERP study

In the present study, we explored the influence of emotional words on the semantic integration of their following neutral nouns during sentence comprehension. We manipulated the emotionality of verbs and the semantic congruity of their following (neutral) object nouns in sentences. Event-related potentials were recorded to the verbs, which were either negative or neutral, and to the object nouns, which were either semantically congruent or incongruent relative to the preceding contexts. We found an N400 and a P600 effect in response to the semantic congruity of the nouns when they followed the neutral verbs. However, the P600 (but not the N400) semantic congruity effect may have been attenuated when the nouns followed the negative verbs. Meanwhile, the negative verbs elicited a larger P2 and N400 than did the neutral verbs. The results indicate that the attention captured by emotional words impaired reanalysis of the following incongruent information, demonstrating a dynamic influence of emotional words on the semantic processing of following information during sentence comprehension.     

Age, working memory, and on-line syntactic processing in sentence comprehension

One hundred twenty-seven individuals who ranged in age from 18 to 90 years were tested on a reading span test and on measures of on-line and off-line sentence processing efficiency. Older participants had reduced working-memory spans compared with younger participants. The on-line measures were sensitive to local increases in processing load, and the off-line measures were sensitive to the syntactic complexity of the sentences. Older and younger participants showed similar effects of syntactic complexity on the on-line measures. There was some evidence that older participants were more affected than younger participants by syntactic complexity on the off-line measures. The results support the hypothesis that on-line processes involved in recognizing linguistic forms and determining the literal, preferred, discourse-coherent meaning of sentences constitute a domain of language processing that relies on its own processing resource or working-memory system.     

Evoked potentials and the study of sentence comprehension

Evoked brain potentials were used to monitor moment-by-moment decisions during language comprehension. Subjects read sentences containing temporary syntactic ambiguities for which one of the possible interpretations was semantically implausible. The N400 component of the evoked potential, which is sensitive to implausibility, was used to discover when during a sentence subjects made a decision about the ambiguity. The results demonstrate that readers try to interpret a syntactic ambiguity early in a sentence rather than waiting for disambiguating information. This introduces a new way to use brain activity to study sentence comprehension processes.     

An on-line assessment of causal reasoning during comprehension

Fletcher and Bloom (1988) have argued that as readers read narratives, clause by clause, they repeatedly focus their attention on the last preceding clause that contains antecedents but no consequences in the text. This strategy allows them to discover a causal path linking the text's opening to its final outcome while minimizing the number of times long-term memory must be searched for missing antecedents or consequences. In order to test this hypothesis, we examined the reading times of 25 subjects for each clause of eight simple narrative texts. The results show that: (1) causal links between clauses that co-occur in short-term memory (as predicted by the strategy) increase the time required to read the second clause; (2) potential causal links between clauses that never co-occur in short-term memory (again as predicted by the strategy) have no effect on reading time; and (3) reinstatement searches are initiated at the end of sentences that are causally unrelated to the contents of short-term memory or that contain clauses that satisfy goals no longer in short-term memory. These results support the claim that subjects engage in a form of causal reasoning when they read simple narrative texts.     

Context effects in sentence comprehension: A study of the subjective lexicon

These studies explore the role of context in determining what information about the meanings of words is activated in memory at the time a word is encountered in a sentence. Using a color-naming paradigm, it was shown that both meanings of a word that has two distinct meanings are activated in memory at the time the word is heard in a sentence. This activation occurs even when there is sufficient contextual information to indicate which meaning was intended by the speaker. These results support the hypothesis that there exists in memory an isolable subjective lexicon. They suggest that context which is effective in disambiguating lexical ambiguities in the language has its effect only at a relatively late stage in the cognitive processing involved in language comprehension.     

Verb processing during sentence comprehension: Contextual impenetrability

This paper examines verb processing during sentence comprehension. We describe two experiments that assess the interaction between verb complexity and the structural information contained in a sentence. Verb complexity is defined in terms of a verb's possible argument structure arrangements—linguistic information arrayed against a verb's entry in the mental lexicon. Normal subjects had to perform a secondary task presented in the immediate vicinity of the verb while listening to a sentence for meaning. Reaction times to this secondary task show that all of a verb's possible argument structures are momentarily and exhaustively activated in the vicinity of the verb, even in sentences that are structurally biased toward one particular argument structure. We thus argue that verb processing in sentences involves a contextually impenetrable subcomponent of the language comprehension system.Program in Linguistics and Cognitive Science, Department of Psychology, Brandeis University.     

Parallel structure: A source of facilitation in sentence comprehension

Reading time for the second clause of a conjoined sentence was found to be faster when the clause was structurally similar to the first clause than when the clausal structures differed. This “parallel structure” effect was found for each of several types of structures, including active versus passive constructions, direct object versus sentential complement (minimal vs. nonminimal attachment), nonshifted versus shifted heavy noun phrase, agent versus theme, and animate versus inanimate noun phrase. The pervasiveness of the effect ruled out some hypotheses about its basis, including the hypothesis that it would occur only when a subject’s just having processed a structure would affect how temporary ambiguities are resolved. Detailed analysis of the data suggested the existence of several distinct sources of the effect and provided indirect evidence that people typically compute both a surface structure and an S-structure representation of a sentence.     

Interpretation-based processing: a unified theory of semantic sentence comprehension

We present interpretation-based processing—a theory of sentence processing that builds a syntactic and a semantic representation for a sentence and assigns an interpretation to the sentence as soon as possible. That interpretation can further participate in comprehension and in lexical processing and is vital for relating the sentence to the prior discourse. Our theory offers a unified account of the processing of literal sentences, metaphoric sentences, and sentences containing semantic illusions. It also explains how text can prime lexical access. We show that word literality is a matter of degree and that the speed and quality of comprehension depend both on how similar words are to their antecedents in the preceding text and how salient the sentence is with respect to the preceding text. Interpretation-based processing also reconciles superficially contradictory findings about the difference in processing times for metaphors and literals. The theory has been implemented in ACT-R [Anderson and Lebiere, The Atomic Components of Thought, Lawrence Erlbaum Associates Publishers, Mahwah, NJ, 1998].     

Focus identification during sentence comprehension: Evidence from eye movements

Three eye movement experiments investigated focus identification during sentence comprehension. Participants read dative or double-object sentences (i.e., either the direct or indirect object occurred first), and a replacive continuation supplied a contrast that was congruous with either the direct or the indirect object. Experiments 1 and 2 manipulated focus by locating only adjacent to either the direct or indirect object of dative (Experiment 1) or double-object (Experiment 2) sentences. Reading-time effects indicated that the surface position of the focus particle influenced processing. In addition, Experiment 1 reading times were longer when the replacive was incongruous with the constituent that only adjoined, and particle position modulated a similar effect in Experiment 2. Experiment 3 showed that this effect was absent when only was omitted. We conclude that the surface position of a focus particle modulates focus identification during on-line sentence comprehension.     

Conceptual combination during sentence comprehension: evidence for compositional processes

This experiment examined the time course of integration of modifier-noun (conceptual) combinations during auditory sentence comprehension using cross-modal lexical priming. The study revealed that during ongoing comprehension, there is initial activation of features of the noun prior to activation of (emergent) features of the entire conceptual combination. These results support compositionality in conceptual combination; that is, they indicate that features of the individual words constituting a conceptual combination are activated prior to combination of the words into a new concept.     

Filling gaps: Decision principles and structure in sentence comprehension

The correct grammatical characterization of sentences containing filler-gap dependencies is a topic of considerable theoretical interest in linguistics. In some grammatical frameworks, these dependencies are representef in terms of conditions on the permissible indexing of structures (or alternative structure evaluation conditions) which a representation must adhere to in order to be well-formed. In other frameworks, constraints on permissible filler-gap dependencies are simply inherent in the set of phrase structure rules contained in the grammar of a language.The processing of sentences with multiple (potential) filler-gap dependencies was investigated in two experiments. The first experiment provided evidence for three claims. First, the human sentence processor abides by a strategy of assigning the most recent potential filler to a gap. Hence, ‘recent filler’ sentences where this assignment proves to be correct takes less time to comprehend than ‘distant filler’ sentences where this decision turns out to be incorrect. Second, the recent filler strategy is itself just a special case of a more general strategy of assigning the most salient potential filler to a gap. Third, unambiguous sentences in which a filler-gap assignment is disambiguated by ‘control’ information specified by individual verbs gives rise to the same recent filler errors as ambiguous sentences. This suggests that tentative filler-gap assignments are made by the processor before all of the relevant constraints on permissible filler-gap dependencies are consulted by the processor.The second experiment tested an alternative hypothesis that the more complex ‘distant filler’ sentences took longer to comprehend in the first experiment only because these sentences often contained verbs which license two adjacent gaps. The experiment showed that there was a significant recent filler effect in sentences that did not contain adjacent gaps and that this effect did not interact with verb class.The finding that the processor delays use of verb-control information is extremely surprising. It may be explained by the fact that this information is only relevant to one type of gap (‘equi-gaps’) and what type of gap the processor is dealing with often can not be determined unambiguously at the time when it initially encounters a gap in its left-to-right processing of a sentence.If our interpretation of these findings is correct, they argue for a considerable amount of structure in the sentence comprehension system. Further, they favor a view of sentence processing in which processing operations involving constraints on the permissible indexing (or evaluation) of structures lag behind the processor's structure building operations. Hence, the results favor those grammatical theories which preserve this distinction over grammatical theories which provide a uniform characterization of all syntactic well-formedness conditions.     

Focus identification during sentence comprehension: evidence from eye movements

Three eye movement experiments investigated focus identification during sentence comprehension. Participants read dative or double-object sentences (i.e., either the direct or indirect object occurred first), and a replacive continuation supplied a contrast that was congruous with either the direct or the indirect object. Experiments 1 and 2 manipulated focus by locating only adjacent to either the direct or indirect object of dative (Experiment 1) or double-object (Experiment 2) sentences. Reading-time effects indicated that the surface position of the focus particle influenced processing. In addition, Experiment 1 reading times were longer when the replacive was incongruous with the constituent that only adjoined, and particle position modulated a similar effect in Experiment 2. Experiment 3 showed that this effect was absent when only was omitted. We conclude that the surface position of a focus particle modulates focus identification during on-line sentence comprehension.     

Computational principles of working memory in sentence comprehension

Understanding a sentence requires a working memory of the partial products of comprehension, so that linguistic relations between temporally distal parts of the sentence can be rapidly computed. We describe an emerging theoretical framework for this working memory system that incorporates several independently motivated principles of memory: a sharply limited attentional focus, rapid retrieval of item (but not order) information subject to interference from similar items, and activation decay (forgetting over time). A computational model embodying these principles provides an explanation of the functional capacities and severe limitations of human processing, as well as accounts of reading times. The broad implication is that the detailed nature of cross-linguistic sentence processing emerges from the interaction of general principles of human memory with the specialized task of language comprehension.     

Brain activation during the course of sentence comprehension

The purpose of this study is to determine, by functional magnetic resonance imaging, how the activated regions of the brain change as a Japanese sentence is presented in a grammatically correct order. In this study, we presented constituents of a sentence to Japanese participants one by one at regular intervals. The results showed that the left lingual gyrus was significantly activated at the beginning of the sentence, then the left inferior frontal gyrus and left supplementary motor area, in the middle of the sentence, and the left inferior temporal gyrus, at the end of the sentence. We suggest that these brain areas are involved in sentence comprehension in this temporal order.     

Decision processes during sentence comprehension: Effects of surface structure reconsidered

Previous experiments have yielded conflicting results concerning the utility of relative pronouns as cues to the deep structure underlying self-embedded (SE) sentences. The present study investigated the usefulness of this cue. At the same time, it compared the relative sensitivity of two measures of sentence-comprehension difficulty: paraphrasing and phoneme monitoring. Forty Ss heard SE sentences, one-half of which had the relative pronouns deleted. The presence or absence of the relative pronouns in a particular sentence was counterbalanced across groups. The Ss also heard right-branching sentences. It was found that presence of the relative pronouns led to significantly faster phoneme monitoring times and to marginally better paraphrasing (i.e., to better comprehension) in the SE sentences. It was concluded that relative pronouns are effective cues and, further, that the phoneme monitoring technique is a better index of comprehension difficulty than the paraphrasing technique. Reasons for the previous experimental discrepancies were discussed.     

Interplay between acoustic/phonetic and semantic processes during spoken sentence comprehension: an ERP study

When listening to speech in everyday-life situations, our cognitive system must often cope with signal instabilities such as sudden breaks, mispronunciations, interfering noises or reverberations potentially causing disruptions at the acoustic/phonetic interface and preventing efficient lexical access and semantic integration. The physiological mechanisms allowing listeners to react instantaneously to such fast and unexpected perturbations in order to maintain intelligibility of the delivered message are still partly unknown. The present electroencephalography (EEG) study aimed at investigating the cortical responses to real-time detection of a sudden acoustic/phonetic change occurring in connected speech and how these mechanisms interfere with semantic integration. Participants listened to sentences in which final words could contain signal reversals along the temporal dimension (time-reversed speech) of varying durations and could have either a low- or high-cloze probability within sentence context. Results revealed that early detection of the acoustic/phonetic change elicited a fronto-central negativity shortly after the onset of the manipulation that matched the spatio-temporal features of the Mismatch Negativity (MMN) recorded in the same participants during an oddball paradigm. Time reversal also affected late event-related potentials (ERPs) reflecting semantic expectancies (N400) differently when words were predictable or not from the sentence context. These findings are discussed in the context of brain signatures to transient acoustic/phonetic variations in speech. They contribute to a better understanding of natural speech comprehension as they show that acoustic/phonetic information and semantic knowledge strongly interact under adverse conditions.     

The cortical language circuit: from auditory perception to sentence comprehension

Over the years, a large body of work on the brain basis of language comprehension has accumulated, paving the way for the formulation of a comprehensive model. The model proposed here describes the functional neuroanatomy of the different processing steps from auditory perception to comprehension as located in different gray matter brain regions. It also specifies the information flow between these regions, taking into account white matter fiber tract connections. Bottom-up, input-driven processes proceeding from the auditory cortex to the anterior superior temporal cortex and from there to the prefrontal cortex, as well as top-down, controlled and predictive processes from the prefrontal cortex back to the temporal cortex are proposed to constitute the cortical language circuit.