On-line Sensitivity to Subject-Verb Agreement Violations in Broca′s Aphasics: The Role of Syntactic Complexity and Time

This study examined on-line sensitivity to subject-verb agreement violations in patients with Broca′s aphasia and age-matched controls using a word monitoring paradigm. The agreement violations were couched in either simple or complex syntactic frames. In a first experiment, these syntactic frames were immediately followed by the noun phrase containing the target, whereas in the second experiment a 750-msec separation was introduced. The main finding of the first experiment was that patients with Broca′s aphasia showed an agreement effect only for simple (i.e., conjoined) sentences but not for complex (i.e., embedded) ones, while controls showed the expected agreement effect for both. The results of the second experiment demonstrated further that the 750-msec delay in target presentation abolished the agreement effect in Broca′s aphasics but not in normal controls. The findings are interpreted to suggest that Broca′s suffer from a pathological limitation in parsing capacity, giving rise to a faster than normal decay of syntactic information.     

Broca’s aphasia, verbs and the mental lexicon

Verb production is notoriously difficult for individuals with Broca’s aphasia, both at the word and at the sentence level. An intriguing question is at which level in the speech production these problems arise. The aim of the present study is to identify the functional locus of the impairment that results in verb production deficits in Broca’s aphasia. Levelt’s (1989) model is used as a theoretical framework for this study. Two experiments have been conducted, one on verb movement and one on verbs with alternating transitivity. The results suggest that the functional impairment in Broca’s aphasia should be located in Levelt’s “grammatical encoder.”     

Speech-associated gestures, Broca’s area, and the human mirror system

Speech-associated gestures are hand and arm movements that not only convey semantic information to listeners but are themselves actions. Broca’s area has been assumed to play an important role both in semantic retrieval or selection (as part of a language comprehension system) and in action recognition (as part of a “mirror” or “observation–execution matching” system). We asked whether the role that Broca’s area plays in processing speech-associated gestures is consistent with the semantic retrieval/selection account (predicting relatively weak interactions between Broca’s area and other cortical areas because the meaningful information that speech-associated gestures convey reduces semantic ambiguity and thus reduces the need for semantic retrieval/selection) or the action recognition account (predicting strong interactions between Broca’s area and other cortical areas because speech-associated gestures are goal-direct actions that are “mirrored”). We compared the functional connectivity of Broca’s area with other cortical areas when participants listened to stories while watching meaningful speech-associated gestures, speech-irrelevant self-grooming hand movements, or no hand movements. A network analysis of neuroimaging data showed that interactions involving Broca’s area and other cortical areas were weakest when spoken language was accompanied by meaningful speech-associated gestures, and strongest when spoken language was accompanied by self-grooming hand movements or by no hand movements at all. Results are discussed with respect to the role that the human mirror system plays in processing speech-associated movements.     

Part of speech and phonological form implied in written-word comprehension: Evidence from homograph disambiguation by normal and aphasic subjects

A sentence construction experiment examining the effect of part of speech and phonological form in written-word comprehension is reported. Normal and aphasic subjects had to write sentences incorporating a given word pair, one word was a homograph (e.g., “bank”) whose meaning was context-biased by the other (e.g., “money”/“river”). The effect of three psycholinguistic factors on subjects' performance was questioned: (i) The relative frequency of one meaning of the homograph as compared to the other meaning; (ii) The lexical/syntactic ambiguity (“ball”/“can”); (iii) The same/different phonological forms of the two meanings (“fair”/“bass”). The results are discussed in the framework of a model in which multiple special-purpose procedures are involved in normal processing, some of them being differentially impaired by brain disease in Broca's and Wernicke's aphasics.     

Speech Rate and Syntactic Complexity as Multiplicative Factors in Speech Comprehension by Young and Older Adults

An experiment is reported in which young and older adults heard short English sentences that differed in syntactic complexity and speech rate. The syntactic contrast pitted center-embedded sentences with a subject-relative clause against sentences with center-embedded object-relative clauses. Speech rate was varied using computer time-compression of the speech signal. Both young and older adults showed poorer comprehension accuracy for the more complex object-relative clause sentences than subject-relative sentences, with an age difference appearing only when sentences were presented at a very rapid rate. By contrast to accuracy scores, older adults took longer than the young adults to give their comprehension responses at all speech rates tested, with this age difference amplified by both speech rate and syntactic complexity.     

Pronominal Resolution and Gap Filling in Agrammatic Aphasia: Evidence from Eye Movements

This paper reports the results of three studies examining comprehension and real-time processing of pronominal (Experiment 1) and Wh-movement (Experiments 2 and 3) structures in agrammatic and unimpaired speakers using eyetracking. We asked the following questions: (a) Is off-line comprehension of these constructions impaired in agrammatic listeners?, (b) Do agrammatic, like unimpaired, listeners show eye movement patterns indicative of automatic pronominal reference resolution and/or gap-filling?, and (c) Do eyetracking patterns differ when sentences are correctly versus incorrectly interpreted, or do automatic processes prevail in spite of comprehension failure? Results showed that off-line comprehension of both pronoun and Wh-movement structures was impaired in our agrammatic cohort. However, the aphasic participants showed visual evidence of real-time reference resolution as they processed binding structures, including both pronouns and reflexives, as did our unimpaired control participants. Similarly, both the patients and the control participants showed patterns consistent with successful gap filling during processing of Wh-movement structures. For neither pronominal nor movement structures did we find evidence of delayed processing. Notably, these patterns were found for the aphasic participants even when they incorrectly interpreted target sentences, with the exception of object relative constructions. For incorrectly interpreted sentences, we found end of sentence lexical competition effects. These findings indicate that aberrant lexical integration, rather than representational deficits or generally slowed processing, may underlie agrammatic aphasic listener’s comprehension failure.     

The uses of short-term memory: A case study

It has been widely claimed that the systems employed in tasks of immediate memory have a function in the comprehension of speech; these systems, it has been proposed, are used to hold a representation of the speech until a syntactic analysis and interpretation have been completed. Such a holding function is meant to be especially important where the sentences heard are long or complex. It has thus been predicted that subjects with impaired short-term memory performance would show deficits in comprehension of such materials.

In this study, one subject with impaired phonological processing and a severely reduced digit span was tested on a range of tasks requiring the syntactic analysis, memory and comprehension of long and complex material. She was found to be unimpaired on syntactic analysis and comprehension, but not on sentence repetition. The implications for models of short-term memory are discussed.     

The effects of slowed speech on auditory comprehension in aphasia

The present study investigates the effects of slowed speech on auditory comprehension in aphasia. Specifically, an attempt was made to isolate the effects of added time on comprehension at the language processing stages of auditory perception, by increasing the duration of the vowel segments in each word; word recognition and semantic analysis, by adding silences between words; and syntactic analysis, by adding silences at constituent phrase boundaries. Sentences were also read at a slow rate to see the effects of naturally slowed speech on sentence comprehension. Test sentences consisted of simple active and passive declarative sentences, and complex sentences with embedded medial and final relative clauses. Sentences were either semantically reversible or nonreversible. Thirty-four aphasic patients who varied in both severity and type of aphasia were tested on a picture verification task. Results indicated that slowing facilitated language comprehension significantly only in the syntactic condition. Neither syntactic complexity nor semantic reversibility interacted with slowed speech to facilitate auditory language comprehension. Further, it was only the Wernicke's aphasics who showed significant improvement with time added at constituent boundaries. These results suggest that time alone does not facilitate language comprehension in aphasia, but that rather it is the interaction of time with syntactic processing which improves comprehension.     

Give and take: syntactic priming during spoken language comprehension

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

Presupposition and Implication of Truth: Linguistic Deficits following Early Brain Lesions

Twenty-four children (4–17 years) with unilateral left (N = 14) or right (N = 10) hemisphere damage and 24 age-matched controls were tested on their ability to presuppose the truth of factive sentences e.g., “Max knew that he locked the door,” and to infer the truth or falsity of implicative sentences “Max remembered to lock the door.” Experimental sentence types varied according to the type of inference, the semantic features of the verb (factive vs. implicative), the presence and type of negation (lexical or syntactic), and the syntax of the complement (tensed or infinitive). Relative to age-matched controls, left lesion subjects were deficient in both their presupposition and implication performance, particularly when such inferences required the computation of negation scope. Right lesion subjects exhibited a somewhat more selective deficit; one limited to implication, but not presupposition, and one limited to lexical but not syntactic forms of negation.     

The Processing of Non-canonically Ordered Constituents in Long Distance Dependencies by Pre-school Children: a Real-time Investigation

Four experiments were performed which had the goal of determining how and when young children acquire the ability to understand long distance dependencies. These studies examined the operations underlying the auditory processing of non-canonically ordered constituents in object-relative sentences. Children 4–6 years of age and an adult population participated in the study, which employed a cross modal picture priming methodology to determine when constituents in a non-canonical position are reactivated during ongoing sentence comprehension. The results support the view that even very young children have the same structural processing reflex seen in adults. Namely, children re-activate a non-canonically positioned (fronted) direct object NP immediately at the post-verb gap site during sentence processing.     

Examining the Empirical and Linguistic Bases of Current Theories of Agrammatism

This paper, which is organized into five sections, critically examines the empirical support and linguistic assumptions underlying several current accounts of language disturbances in Broca′s aphasia. In the first section, following a discussion of the use of signal detection methodologies in investigating grammatical sensitivity, the reliability of results from two studies that suggest that Broca′s aphasic patients are differentially sensitive to grammatical constraints is examined. It is concluded that in some cases, claims of intact sensitivity are not supported. The second section examines the empirical support for the hypothesis that agrammatic patients are unable to compute syntactic dependency relationships because of slowed lexical processing. It is argued that the statistical treatment of the data and interpretive problems associated with the lexical decision paradigm undermine this hypothesis. In the third section, some of the linguistic assumptions underlying criticisms of chain-disruption hypotheses are examined. It is concluded that these criticisms are based on arguable linguistic assumptions. In the fourth section, it is argued that the linguistic and empirical support for both earlier and revised versions of Grodzinsky′s default interpretive strategy is lacking. Methodological and conceptual shortcomings arising from this proposal are also discussed. In the final section, potential relationships between disordered language and currently developing models of normal language processing are discussed.     

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.     

Real-time comprehension of wh- movement in aphasia: evidence from eyetracking while listening

Sentences with non-canonical wh- movement are often difficult for individuals with agrammatic Broca's aphasia to understand (, inter alia). However, the explanation of this difficulty remains controversial, and little is known about how individuals with aphasia try to understand such sentences in real time. This study uses an eyetracking while listening paradigm to examine agrammatic aphasic individuals' on-line comprehension of movement sentences. Participants' eye-movements were monitored while they listened to brief stories and looked at visual displays depicting elements mentioned in the stories. The stories were followed by comprehension probes involving wh- movement. In line with previous results for young normal listeners [Sussman, R. S., & Sedivy, J. C. (2003). The time-course of processing syntactic dependencies: evidence from eye movements. Language and Cognitive Processes, 18, 143-161], the study finds that both older unimpaired control participants (n=8) and aphasic individuals (n=12) showed visual evidence of successful automatic comprehension of wh- questions (like "Who did the boy kiss that day at school?"). Specifically, both groups fixated on a picture corresponding to the moved element ("who," the person kissed in the story) at the position of the verb. Interestingly, aphasic participants showed qualitatively different fixation patterns for trials eliciting correct and incorrect responses. Aphasic individuals looked first to the moved-element picture and then to a competitor following the verb in the incorrect trials. However, they only showed looks to the moved-element picture for the correct trials, parallel to control participants. Furthermore, aphasic individuals' fixations during movement sentences were just as fast as control participants' fixations. These results are unexpected under slowed-processing accounts of aphasic comprehension deficits, in which the source of failed comprehension should be delayed application of the same processing routines used in successful comprehension. This pattern is also unexpected if aphasic individuals are using qualitatively different strategies than normals to comprehend such sentences, as under impaired-representation accounts of agrammatism. Instead, it suggests that agrammatic aphasic individuals may process wh- questions similarly to unimpaired individuals, but that this process often fails to facilitate off-line comprehension of sentences with wh- movement.     

Comprehension of gerundive constructions by Broca's aphasics

Eleven diagnosed Broca's aphasics were tested for comprehension of sentences containing gerundive constructions. Results showed that, as a group, these patients were sensitive to grammatical distinctions signaled by “function” words, contrary to the predictions of some current theories about the specific deficits exhibited in this syndrome. Further analysis showed that the patients fell into two subgroups, one which exhibited sensitivity to the distinctions in normal grammar, and another which exhibited no sensitivity to such distinctions. This suggests that the syndrome may have different manifestations in different populations—patient age is suggested as a possible means for distinguishing the two groups. Suggestions for further research into the nature of the comprehension deficits exhibited by Broca's aphasics are made.     

Speed of Lexical Activation in Nonfluent Broca''s Aphasia and Fluent Wernicke''s Aphasia

Rapid, automatic access to lexical/semantic knowledge is critical in supporting the tight temporal constraints of on-line sentence comprehension. Based on findings of “abnormal” lexical priming in nonfluent aphasics, the question of disrupted automatic lexical activation has been the focus of many recent efforts to understand their impaired sentence comprehension capabilities. The picture that emerges from this literature is, however, unclear. Nonfluent Broca's aphasic patients showinconsistent,notabsent,lexical priming, and there is little consensus about the conditions under which they do and do not prime. The most parsimonious explanation for the variable findings from priming studies to date is that the primary disturbance in Broca's lexical activation has something to do withspeedof activation. Broca's aphasic patients prime when sufficient time is allowed for activation to spread among associates. To examine this “slowed activation” hypothesis, the time course of lexical activation was examined using a list priming paradigm. Temporal delays between successive words ranged from 300 to 2100 msec. One nonfluent Broca's aphasic patient and one fluent Wernicke's patient were tested. Both patients displayed abnormal priming patterns, though of different sorts. In contrast to elderly subjects, who prime at relatively short interstimulus intervals (ISIs) beginning at 500 msec, the Broca's aphasic subject showed reliable automatic priming but only at a long ISI of 1500 msec. That is, this subject retained the ability to access lexical information automatically if allowed sufficient time to do so, a finding that may help explain disrupted comprehension of normally rapid conversational speech. The Wernicke's aphasic subject, in contrast, showed normally rapid initial activation but continued to show priming over an abnormally long range of delays, from 300 msec through 1100 msec. This protracted priming suggests failure to dampen activation and might explain the semantic confusion exhibited by fluent Wernicke's patients.     

The role of Broca's area in speech perception: evidence from aphasia revisited

Motor theories of speech perception have been re-vitalized as a consequence of the discovery of mirror neurons. Some authors have even promoted a strong version of the motor theory, arguing that the motor speech system is critical for perception. Part of the evidence that is cited in favor of this claim is the observation from the early 1980s that individuals with Broca’s aphasia, and therefore inferred damage to Broca’s area, can have deficits in speech sound discrimination. Here we re-examine this issue in 24 patients with radiologically confirmed lesions to Broca’s area and various degrees of associated non-fluent speech production. Patients performed two same-different discrimination tasks involving pairs of CV syllables, one in which both CVs were presented auditorily, and the other in which one syllable was auditorily presented and the other visually presented as an orthographic form; word comprehension was also assessed using word-to-picture matching tasks in both auditory and visual forms. Discrimination performance on the all-auditory task was four standard deviations above chance, as measured using d′, and was unrelated to the degree of non-fluency in the patients’ speech production. Performance on the auditory–visual task, however, was worse than, and not correlated with, the all-auditory task. The auditory–visual task was related to the degree of speech non-fluency. Word comprehension was at ceiling for the auditory version (97% accuracy) and near ceiling for the orthographic version (90% accuracy). We conclude that the motor speech system is not necessary for speech perception as measured both by discrimination and comprehension paradigms, but may play a role in orthographic decoding or in auditory–visual matching of phonological forms.     

Parametric effects of syntactic-semantic conflict in Broca's area during sentence processing

The hypothesized role of Broca’s 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 Broca’s area regions of interest reflected the parametric variation in syntactic-semantic conflict. These results suggest that Broca’s area supports sentence processing by mediating between multiple incompatible constraints on sentence interpretation, consistent with this area’s well-known role in conflict resolution in other linguistic and non-linguistic tasks.     

Syntactic priming effects in aphasia: an investigation of local syntactic dependencies

This study explored on-line processing of local syntactic dependencies in normal subjects and in Broca's and Wernicke's aphasics using a lexical decision paradigm. In addition, subjects performed a grammatically judgement task on the real word pairs used in the lexical decision tasks. Results of two experiments for normal subjects indicated different syntactic priming effects as a function of the type of local syntactic dependency. Word pairs that formed a single constituent phrase, i.e., a verb phrase, showed both facilitory and inhibitory effects, whereas word pairs that reflected local syntactic dependencies across a phrase boundary, i.e., pronoun verb, showed only inhibitory effects. Broca's aphasics failed to show facilitory effects when presented with word pairs forming a single constituent phrase but, similar to normals, did show inhibition when presented with word pairs that reflected local syntactic dependencies across a phrase boundary. In contrast, Wernicke's aphasics failed to show inhibitory effects in both experiments. The implications of these results for theories of language processing deficits in aphasia are considered.