Inflection and computational load in agrammatic speech

In this study we investigate the production of verb inflection in agrammatic aphasia. In a number of recent studies it has been argued that tense inflection is harder to produce for agrammatic individuals than agreement inflection. However, results are still inconclusive, at least for Dutch and German. Here, we report three experiments in which this matter is further investigated. Our first goal was to determine whether tense was indeed more difficult to produce than agreement. Also, we investigated whether error rates were influenced by computational load. The results for nine Dutch-speaking agrammatic participants generally indicated that tense was indeed harder to produce than agreement, but that for both types of inflection, the number of errors increased with computational load. Taking care of word order and inflection induced more errors than taking care of just inflection. These findings are discussed in relation to current processing and representational models of agrammatic production.     

Agrammatic sentence production: is verb second impaired in Dutch?

This study investigates effects of verb movement in nine Dutch-speaking agrammatic aphasics. According to linguistic theory, in verb second languages such as Dutch and German, the verb remains in its clause-final base position in embedded clauses, whereas it moves to second position in main clauses. In recent linguistic accounts of agrammatic sentence production, it has been suggested that the production of sentences with moved verbs is relatively difficult. However, we argue that evidence provided by previous studies on this matter is inconclusive. An experiment is reported in which the production of both types of clauses is compared. No evidence is found that sentences with moved verbs are relatively difficult to produce. In fact, there was a tendency for the base order sentences to be harder. Implications of these findings for theories of normal and agrammatic sentence production are discussed.     

Production of non-canonical sentences in agrammatic aphasia: limits in representation or rule application?

The study reported here compares two linguistically informed hypotheses on agrammatic sentence production, the TPH [Friedmann, N., & Grodzinsky, Y. (1997). Tense and agreement in agrammatic production: Pruning the syntactic tree. Brain and Language, 56, 397-425.] and the DOP [Bastiaanse, R., & van Zonneveld, R. (2005). Sentence production with verbs of alternating transitivity in agrammatic Broca's aphasia. Journal of Neurolinguistics, 18, 59-66]. To explain impaired production of non-canonical sentences in agrammatism, the TPH basically relies on deleted or pruned clause structure positions in the left periphery, whereas the DOP appeals to limitations in the application of movement rules. Certain non-canonical sentences such as object-questions and object-relative clauses require the availability of nodes in the left periphery as well as movement to these nodes. In languages with relatively fixed word order such as English, the relevant test cases generally involve a coincidence of left periphery and movement, such that the predictions of the TPH and the DOP are identical although for different reasons. In languages with relatively free word order such as German, on the other hand, it is possible to devise specific tests of the different predictions due to the availability of scrambling. Scrambled object sentences, for example, do not involve the left periphery but do require application of movement in a domain below the left periphery. A study was conducted with German agrammatic subjects which elicited canonical sentences without object movement and non-canonical scrambled sentences with object movement. The results show that agrammatic speakers have a particular problem with the production of scrambled sentences. Further evidence reported in the study from spontaneous speech, elicitation of object relatives, questions and passives and with different agrammatic subjects confirms that non-canonical sentences are generally harder to produce for agrammatics. These findings provide evidence in favor of the DOP and it will be argued that a cross-modal explanation of agrammatic deficits is possible if two factors--movement and canonicity--are taken into consideration.     

Tense and Agreement dissociations in German agrammatic speakers: underspecification vs. hierarchy

The aim of the present paper was to investigate whether German agrammatic production data are compatible with the Tree-Pruning-Hypothesis (TPH; Friedmann & Grodzinsky, 1997). The theory predicts unidirectional patterns of dissociation in agrammatic production data with respect to Tense and Agreement. However, there was evidence of a double dissociation between Tense and Agreement in our data. The presence of a bidirectional dissociation is incompatible with any theory which assumes a hierarchical order between these categories such as the TPH or other versions thereof (such as Lee's, 2003 top--down hypothesis). It will be argued that the data can better be accounted for by relying on newer linguistic theories such as the Minimalist Program (MP,), which does not assume a hierarchical order between independent syntactic Tense and Agreement nodes but treats them as different features (semantically interpretable vs. uninterpretable) under a single node.     

Neural correlates of Dutch Verb Second in speech production

Dutch speakers with agrammatic Broca's aphasia are known to have problems with the production of finite verbs in main clauses. This performance pattern has been accounted for in terms of the specific syntactic complexity of the Dutch main clause structure, which requires an extra syntactic operation (Verb Second), relative to the basic Subject-Object-Verb order surfacing in Dutch subordinate clauses. We report an fMRI study into the question whether this syntactic complexity is reflected in increased brain activation correlated with the production of Dutch main clause word order, in speakers without language impairment. Nineteen healthy subjects performed a covert sentence completion task, during which main and subordinate clauses were alternately elicited in a block design. Results show a left middle to superior frontal cluster of activation correlated to production of Verb-Second over Verb-Final clauses, with no activation in the opposite contrast. This activation pattern is counter to what might be expected from the frequency distribution of main and subordinate clauses. We conclude that the Verb-Second deviation from the basic Dutch SOV word order costs extra neural resources and that this also underlies the agrammatic problems with the production of finite verbs in Dutch main clauses.     

Time reference through verb inflection in Turkish agrammatic aphasia

This study tested the production of tensed finite verbs and participles referring to the past and future in agrammatic speakers of Turkish. The agrammatic speakers did not make more time reference errors in tensed verbs than in participles. This is interesting because tense in general cannot therefore be the main problem, since time reference for participles lacking tense inflection is as difficult as for verbs with tense inflection. Besides that, the past tense/perfect aspect was found to be more difficult to produce for the agrammatic speakers than the future tense/imperfect aspect. None of the current theories on agrammatic deficits can explain why reference to the past/perfect aspect is more difficult than reference to future/imperfect aspect, although a similar finding was reported for Dutch by Bastiaanse [Bastiaanse, R. (2008). Production of verbs in base-position by Dutch agrammatic speakers: Inflection versus finiteness. Journal of Neurolinguistics, 21, 104-119]. We present a remoteness model of time reference to account for the data.     

Does morphology make the difference? Agrammatic sentence comprehension in German

This study examines the syntactic comprehension of seven German agrammatic speakers. The German language allows the study of the interaction of syntactic principles and morphological devices in the comprehension process. In addition, due to its relatively free word order, German allows the study of strictly minimal pairs of canonical and non-canonical sentences in addition to the rather controversial active-passive contrast. A central research question was whether the pattern of agrammatic comprehension predicted by the trace deletion hypothesis (TDH, Grodzinsky, 1990, 1995), relatively normal comprehension performance of canonical sentences and chance performance on non-canonical sentences, can be found in a language with richer morphology than English. The generalisability of the TDH-pattern to morphologically rich languages is not obvious, given that case morphology in particular can provide explicit cues to the detection of the agent and patient roles in a sentence. The results of this study indicate that morphology does not make a difference. Furthermore, the group results are in line with the TDH-predictions only for number marked sentences but not for case marked sentences. However, single case analysis reveals different patterns of syntactic comprehension in agrammatic patients, a spectrum that encompasses near-normal comprehension of canonical and non-canonical sentences, overall chance performance, and TDH-like profiles.     

Agrammatic aphasic subjects' comprehension of subject and object extracted Wh questions

This study attempted to replicate the unusual wh question comprehension pattern of Hickok and Avrutin's (1996) subjects who showed an expected subject/object extraction asymmetry for which NP questions, but not for who questions. We also examined comprehension of what and which one questions, which are similar to who and which NP questions, respectively, and we examined passivized wh questions in order to test predictions of Grodzinsky's (1995) restrictive theory of trace deletion, the Trace-Based Account (TBA). Results, using both a figurine manipulation task and a picture pointing task, showed that only one of four agrammatic (Broca's) aphasic subjects showed the pattern reported by Hickok and Avrutin and that this pattern extended to comprehension of what and which one questions. One of the subjects showed subject/object asymmetry for all wh questions tested, as would be predicted by the original trace deletion hypothesis (Grodzinsky, 1984), and two subjects showed neither pattern. None of our subjects demonstrated ability to comprehend passivized wh questions as predicted by the TBA. We discuss our findings in terms of the lack of homogeneity of wh question comprehension among individuals with agrammatic aphasia and we explore alternatives to the syntactic explanation for differences between who and which NP question comprehension advanced by Hickok and Avrutin.     

Mental representation of prepositional compounds: evidence from Italian agrammatic patients

The processing of Prepositional compounds (typical Neo-latin noun--noun modifications where a head noun is modified by a prepositional phrase, e.g., mulino a vento, windmill) was preliminarily studied with a group of six agrammatic aphasic patients, and, in more detail, with a further agrammatic patient (MB). Omission was the most frequent error type in naming, whereas in the other tasks (repetition, reading, writing, and completion) errors were mostly substitutions of the target preposition. This happened even with fully lexicalized compound forms, i.e., those forms where the linking preposition is syntactically and semantically opaque. These findings are interpreted in terms of a dual-route theory of lexical access to morphologically complex words.     

Understanding Disorders in Agrammatic Patients: Capacity or Structural Deficits?

Several hypotheses have been advanced in recent years to understand difficulties in agrammatic patients. Some of them are of a structural kind, as the deficiency is said to lie in some of the linguistic system components. Others are of a functional type, as it is stated that the problem of these patients lies in the loss of processing capacity.Using the existence of a syntactic type of structure in Spanish, that active sentences do not follow the canonical S-V-O order, we will try to prove in this article whether agrammatic patients' problems are due to memory span loss or to one of the syntactic process mechanisms. To this end, the performances of three groups of patients are contrasted. Agrammatic, anomic, and normal Spanish speakers are given several tasks of sentence–picture matching and tests of memory span.Results show that agrammatic patients have specific difficulties processing certain syntactical structures; however, their memory deficiencies are not more pronounced than in other patients. It can be concluded, therefore, that the deficiencies of agrammatic patients are of a structural character rather than due to memory span loss.     

The word order problem in agrammatism : II. Production

This study demonstrates that agrammatic aphasics have difficulty describing relations that are signified by the order of noun phrases around verbs or prepositions. The word order deficit is found in a Sentence Order Task, in which written words must be arranged linearly to form a sentence, as well as in oral production. Ordering tendencies reflect factors like animacy or potency, rather than the systematic use of syntactic rules. These results point to a fundamental syntactic disorder in agrammatism.     

A note on the "word-order problem" in agrammatism

This brief note has two parts. First, it presents an analysis of the ability of English agrammatic patients to assign the thematic roles of agent, instrument, theme, and locative to noun phrases in active and passive sentences and prepositional phrases. Data regarding this ability have been presented by Schwartz, Saffran, and Marin (Brain and Language, 10, 149-262 (1980) regarding comprehension, and by Saffran, Schwartz, and Marin (Brain and Language, 10, 263-280 (1980) regarding production. These authors claim their data show that English agrammatic aphasics do not map "word order" onto thematic information. However, a very simple set of principles accounts for all their results, including results which are discrepant in their treatment, but requires that English agrammatics assign thematic roles to NPs in part by virtue of the position of an NP in a sentence or a phrase. In the second part of this note, several issues raised by this re-analysis are briefly discussed.     

Syntactic comprehension deficits in agrammatism

Eleven agrammatic and 16 fluent aphasic patients were given a comprehension task consisting of simple, active and passive reversible sentences. The purpose of the study is to reconsider the comprehension disorders in agrammatism, and particularly of passive reversible sentences, to test to what extent Grodzinsky's trace deletion hypothesis (TDH) is generalizable to other types of NP-movement, and finally to ascertain whether the pattern of impairment observed in agrammatism differs from that of fluent aphasic patients. The study confirms that trace analysis may be selectively impaired in agrammatism. However, this deficit is not the only mechanism underlying comprehension disorders and cannot be said to occur in all agrammatic patients. Comprehension disorders also involve the processing of clitic object pronouns which also underly NP-movement. Finally, the impairment found in fluent aphasic patients differs, both in type and severity, from that of agrammatic patients, thus confirming the peculiar aspects of the agrammatic comprehension deficit suggested by Grodzinsky's TDH.     

The production of Turkish relative clauses in agrammatism: Verb inflection and constituent order

This study presents results from a sentence completion test that examines the production of finite main clauses and non-finite relative clauses in Turkish agrammatic speech. In main clauses, the verb is finite and all its constituents are in their base positions. In relative clauses, the verb is a participle and the NP undergoes overt movement to an A-bar position. The results show that non-finite relative clauses with overt movement as such are more difficult to produce than finite main clauses with a base order. The findings are discussed with respect to several hypotheses on finite verbs and syntactic complexity. The conclusion is that Turkish agrammatic speakers have more problems in producing structurally derived clauses and the production of verbs is influenced by linguistic factors such as the overt movement of the NP.     

Implicit and Explicit Learning in Individuals with Agrammatic Aphasia

Implicit learning is a process of acquiring knowledge that occurs without conscious awareness of learning, whereas explicit learning involves the use of overt strategies. To date, research related to implicit learning following stroke has been largely restricted to the motor domain and has rarely addressed implications for language. The present study investigated implicit and explicit learning of an auditory word sequence in 10 individuals with stroke-induced agrammatic aphasia and 18 healthy age-matched participants using an adaptation of the Serial Reaction Time task. Individuals with aphasia showed significant learning under implicit, but not explicit, conditions, whereas age-matched participants learned under both conditions. These results suggest significant implicit learning ability in agrammatic aphasia. Furthermore, results of an auditory sentence span task indicated working memory deficits in individuals with agrammatic aphasia, which are discussed in relation to explicit and implicit learning processes.     

Verb deficits in Alzheimer's disease and agrammatism: implications for lexical organization

This study examined the nature of verb deficits in 14 individuals with probable Alzheimer's Disease (PrAD) and nine with agrammatic aphasia. Production was tested, controlling both semantic and syntactic features of verbs, using noun and verb naming, sentence completion, and narrative tasks. Noun and verb comprehension and a grammaticality judgment task also were administered. Results showed that while both PrAD and agrammatic subjects showed impaired verb naming, the syntactic features of verbs (i.e., argument structure) influenced agrammatic, but not Alzheimer's disease patients' verb production ability. That is, agrammatic patients showed progressively greater difficulty with verbs associated with more arguments, as has been shown in previous studies (e.g., Kim & Thompson, 2000; Thompson, 2003; Thompson, Lange, Schneider, & Shapiro, 1997), and suggest a syntactic basis for verb production deficits in agrammatism. Conversely, the semantic complexity of verbs affected PrAD, but not agrammatic, patients' performance, suggesting "bottom-up" breakdown in their verb lexicon, paralleling that of nouns, resulting from the degradation or loss of semantic features of verbs.