The representation of lexical-syntactic information: evidence from syntactic and lexical retrieval impairments in aphasia

This study explored lexical-syntactic information - syntactic information that is stored in the lexicon - and its relation to syntactic and lexical impairments in aphasia. We focused on two types of lexical-syntactic information: predicate argument structure (PAS) of verbs (the number and types of arguments the verb selects) and grammatical gender of nouns. The participants were 17 Hebrew-speaking individuals with aphasia who had a syntactic deficit (agrammatism) or a lexical retrieval deficit (anomia) located at the semantic lexicon, the phonological output lexicon, or the phonological output buffer. After testing the participants' syntactic and lexical retrieval abilities and establishing the functional loci of their deficits, we assessed their PAS and grammatical gender knowledge. This assessment included sentence completion, sentence production, sentence repetition, and grammaticality judgment tasks. The participants' performance on these tests yielded several important dissociations. Three agrammatic participants had impaired syntax but unimpaired PAS knowledge. Three agrammatic participants had impaired syntax but unimpaired grammatical gender knowledge. This indicates that lexical-syntactic information is represented separately from syntax, and can be spared even when syntax at the sentence level, such as embedding and movement are impaired. All 5 individuals with phonological output buffer impairment and all 3 individuals with phonological output lexicon impairment had preserved lexical-syntactic knowledge. These selective impairments indicate that lexical-syntactic information is represented at a lexical stage prior to the phonological lexicon and the phonological buffer. Three participants with impaired PAS (aPASia) and impaired grammatical gender who showed intact lexical-semantic knowledge indicate that the lexical-syntactic information is represented separately from the semantic lexicon. This led us to conclude that lexical-syntactic information is stored in a separate syntactic lexicon. A double dissociation between PAS and grammatical gender impairments indicated that different types of lexical-syntactic information are represented separately in this syntactic lexicon.     

A selective deficit for inflection production

We report the case of an English-speaking aphasic patient (JP) with left posterior-frontal damage affecting the inferior frontal and precentral gyri. In speaking, JP was impaired with the regular inflections of nouns and pseudonouns, making errors like “pears” instead of pear or “door” for doors, while the spoken production of noun stems and irregularly inflected nouns (teeth) was preserved. JP's noun inflection errors stemmed from problems with inflection selection rather than a lack of understanding of concept numerosity or phonological deficit. Evidence that inflection deficits occur independently of semantic and phonological impairments supports accounts that propose dedicated neural substrates for morphological processes and raises a challenge for connectionist models that do not incorporate specific mechanisms for morphology. JP's results also demonstrated a lexical deficit selectively affecting the retrieval of verb stems and a more severe impairment for verb vs. noun inflections. JP's verb production deficit suggests a close interaction between inflectional and lexical processes probably reflecting the fact that English inflection choice in part depends on stem information stored in the lexicon.     

Dissociation of lexical syntax and semantics: evidence from focal cortical degeneration

The question of whether information relevant to meaning (semantics) and structure (syntax) relies on a common language processor or on separate subsystems has proved difficult to address definitively because of the confounds involved in comparing the two types of information. At the sentence level syntactic and semantic judgments make different cognitive demands, while at the single word level, the most commonly used syntactic distinction (between nouns and verbs) is confounded with a fundamental semantic difference (between objects and actions). The present study employs a different syntactic contrast (between count nouns and mass nouns), which is crossed with a semantic difference (between naturally occurring and man-made substances) applying to words within a circumscribed semantic field (foodstuffs). We show, first, that grammaticality judgments of a patient with semantic dementia are indistinguishable from those of a group of age-matched controls, and are similar regardless of the status of his semantic knowledge about the item. In a second experiment we use the triadic task in a group of age-matched controls to show that similarity judgments are influenced not only by meaning (natural vs. manmade), but also implicitly by syntactic information (count vs. mass). Using the same task in a patient with semantic dementia we show that the semantic influences on the syntactic dimension are unlikely to account for this pattern in normals. These data are discussed in relation to modular vs. nonmodular models of language processing, and in particular to the semantic-syntactic distinction.     

Dissociation of Lexical Syntax and Semantics: Evidence from Focal Cortical Degeneration

Abstract

The question of whether information relevant to meaning (semantics) and structure (syntax) relies on a common language processor or on separate subsystems has proved difficult to address definitively because of the confounds involved in comparing the two types of information. At the sentence level syntactic and semantic judgments make different cognitive demands, while at the single word level, the most commonly used syntactic distinction (between nouns and verbs) is confounded with a fundamental semantic difference (between objects and actions). The present study employs a different syntactic contrast (between count nouns and mass nouns), which is crossed with a semantic difference (between naturally occurring and man-made substances) applying to words within a circumscribed semantic field (foodstuffs). We show, first, that grammaticality judgments of a patient with semantic dementia are indistinguishable from those of a group of age-matched controls, and are similar regardless of the status of his semantic knowledge about the item. In a second experiment we use the triadic task in a group of age-matched controls to show that similarity judgments are influenced not only by meaning (natural vs. manmade), but also implicitly by syntactic information (count vs. mass). Using the same task in a patient with semantic dementia we show that the semantic influences on the syntactic dimension are unlikely to account for this pattern in normals. These data are discussed in relation to modular vs. nonmodular models of language processing, and in particular to the semantic-syntactic distinction.     

How the mass counts: an electrophysiological approach to the processing of lexical features

Nouns may refer to countable objects such as tables, or to mass entities such as rice. The mass/count distinction has been discussed in terms of both semantic and syntactic features encoded in the mental lexicon. Here we show that event-related potentials (ERPs) can reflect the processing of such lexical features, even in the absence of any feature-related violations. We demonstrate that count (vs mass) nouns elicit a frontal negativity which is independent of the N400 marker for conceptual-semantic processing, but resembles anterior negativities related to grammatical processing. This finding suggests that the brain differentiates between count and mass nouns primarily on a syntactic basis.     

Where do semantic errors come from?

We report the performance of two brain-damaged subjects (RGB and HW) whose frequent errors in spoken production are nearly always semantically related to the target word. Both subjects show similar, high rates of these "semantic" errors in oral naming and oral reading; yet neither subject makes semantic errors in comparable written tasks. Further, results of a variety of lexical tasks with the same stimuli demonstrate unimpaired comprehension of printed or spoken words, including those that are orally produced as semantic errors. These patterns of performance are interpreted as resulting from damage to the phonological output lexicon. The postulated deficit is contrasted to the hypothesis of impairment to the lexical-semantic component, required to explain performance by brain-damaged subjects described elsewhere who make seemingly identical types of oral production errors to those of RGB and HW, but, in addition, make comparable errors in writing and comprehension tasks.     

Semantic errors in naming,repetition, spelling and drawing from memory: a new Italian case

Semantic errors in aphasic patients are frequent and their study has helped understanding the structure and processing of the lexical/semantic system. Most of the patients with semantic errors in reading and writing are English-speaking and it has been argued that this depends on the type of the orthographic systems: in opaque orthographies semantic errors are more frequent than in transparent orthographies. The paper reports the case of an Italian patient, AM, with semantic damage and semantic errors in comprehension and production tasks, except reading aloud. AM was also impaired in non-word repetition and writing but his reading of non-words was only mildly impaired. The absence of semantic errors in reading and the co-occurring absence of severe damage to the non-lexical reading route is consistent with interaction between lexical and non-lexical processing. The discussion addresses the question of the relative frequency of semantic errors in reading and writing tasks in languages with different types of orthographies.     

Semantic Errors in Naming,Repetition, Spelling and Drawing from Memory: A New Italian Case

Semantic errors in aphasic patients are frequent and their study has helped understanding the structure and processing of the lexical/semantic system. Most of the patients with semantic errors in reading and writing are English-speaking and it has been argued that this depends on the type of the orthographic systems: in opaque orthographies semantic errors are more frequent than in transparent orthographies. The paper reports the case of an Italian patient, AM, with semantic damage and semantic errors in comprehension and production tasks, except reading aloud. AM was also impaired in non-word repetition and writing but his reading of non-words was only mildly impaired. The absence of semantic errors in reading and the co-occurring absence of severe damage to the non-lexical reading route is consistent with interaction between lexical and non-lexical processing. The discussion addresses the question of the relative frequency of semantic errors in reading and writing tasks in languages with different types of orthographies.     

Single‐word semantic judgements in semantic dementia: Do phonology and grammatical class count?

Background: Listeners make active use of phonological regularities such as word length to facilitate higher‐level syntactic and semantic processing. For example, nouns are longer than verbs, and abstract words are longer than concrete words. Patients with semantic dementia (SD) experience conceptual loss with preserved syntax and phonology. The extent to which patients with SD exploit phonological regularities to support language processing remains unclear.

Aims: We examined the ability of patients with SD (1) to perceive subtle acoustic–phonetic distinctions in English, and (2) to bootstrap their accuracy of lexical‐semantic and syntactic judgements from regularities in the phonological forms of English nouns and verbs.

Methods and Procedures: Four patients with SD made minimal pair judgements (same/different) for auditorily presented stimuli selectively varied by voice, place, or manner of the initial consonant (e.g., pa –ba). In Experiment 2 patients made forced‐choice semantic judgements (abstract or concrete) for single words varied by (1) concreteness (abstract or concrete); (2) grammatical class (noun or verb); and (3) word length (one‐ or three‐syllable words).

Outcomes and Results: The most semantically impaired patients paradoxically showed the highest accuracy of minimal pair phonologic discrimination. Judgements of word concreteness were less accurate for verbs than nouns. Among verbs, accuracy was worse for concrete than abstract items (e.g., eat was worse than think). Patients were more likely to misclassify longer concrete words (e.g., professor) as abstract, demonstrating sensitivity to an underlying phonologically mediated semantic property in English.

Conclusions: Single‐word semantic judgements were sensitive to both grammatical class and phonological properties of the words being evaluated. Theoretical and clinical implications are addressed in the context of an anatomically constrained model of SD that assumes increasing reliance on phonology as lexical‐semantic knowledge degrades.     

When a rose is a rose in speech but a tulip in writing.

We report the pattern of performance on language tasks by a neurologically impaired patient, RCM, who makes semantic errors in writing to dictation and in written naming, but makes very few errors at all (and no semantic errors) in spoken naming, oral reading, or spontaneous speech. RCM also shows a significant effect of concreteness on spelling accuracy and other features of so-called "deep dysgraphia." However, it is shown that, unlike previously reported patients described as deep dysgraphic, RCM has intact semantic processing but impairment in accessing lexical-orthographic representations, at least for the items tested. These results demonstrate that the collection of features labelled as "deep dysgraphia" can arise from damage to different cognitive processes. Detailed analyses of RCM's performance across lexical tasks, at two different time periods of recovery, provide evidence that lexical orthographic representations can be either directly activated by lexical semantic representations, or activated by the interaction of lexical semantic and sublexical information from phonology-to-orthography conversion mechanisms.     

Effects of syntactic cueing therapy on picture naming and connected speech in acquired aphasia

Language therapy for word-finding difficulties in aphasia usually involves picture naming of single words with the support of cues. Most studies have addressed nouns in isolation, even though in connected speech nouns are more frequently produced with determiners. We hypothesised that improved word finding in connected speech would be most likely if intervention treated nouns in usual syntactic contexts. Six speakers with aphasia underwent language therapy using a software program developed for the purpose, which provided lexical and syntactic (determiner) cues. Exposure to determiners with nouns would potentially lead to improved picture naming of both treated and untreated nouns, and increased production of determiner plus noun combinations in connected speech. After intervention, picture naming of treated words improved for five of the six speakers, but naming of untreated words was unchanged. The number of determiner plus noun combinations in connected speech increased for four speakers. These findings attest to the close relationship between frequently co-occurring content and function words, and indicate that intervention for word-finding deficits can profitably proceed beyond single word naming, to retrieval in appropriate syntactic contexts. We also examined the relationship between effects of therapy, and amount and intensity of therapy. We found no relationship between immediate effects and amount or intensity of therapy. However, those participants whose naming maintained at follow-up completed the therapy regime in fewer sessions, of relatively longer duration. We explore the relationship between therapy regime and outcomes, and propose future considerations for research.     

The semantic organisation of mass nouns: evidence from semantic refractory access dysphasia

The conceptual properties and organisation of mass noun concepts are examined in a patient (A.Z.) with a semantic refractory access disorder. A cardinal feature of this class of disorder is the build up of interference (refractoriness) between semantically similar concepts. In a series of written word identification tasks, a gradient of semantic relatedness is demonstrated within the broad domain of mass noun concepts but not between different word classes. More detailed examinations of semantic similarity effects within subcategories of mass concepts reveal a variable degree of fine-grain organisation, which may reflect the influence of premorbid personal knowledge and experience. Furthermore, it is demonstrated that common mass or count noun status did not lead to an enhancement of the refractory effects of semantic similarity.     

Effects of syntactic cueing therapy on picture naming and connected speech in acquired aphasia

Language therapy for word-finding difficulties in aphasia usually involves picture naming of single words with the support of cues. Most studies have addressed nouns in isolation, even though in connected speech nouns are more frequently produced with determiners. We hypothesised that improved word finding in connected speech would be most likely if intervention treated nouns in usual syntactic contexts. Six speakers with aphasia underwent language therapy using a software program developed for the purpose, which provided lexical and syntactic (determiner) cues. Exposure to determiners with nouns would potentially lead to improved picture naming of both treated and untreated nouns, and increased production of determiner plus noun combinations in connected speech. After intervention, picture naming of treated words improved for five of the six speakers, but naming of untreated words was unchanged. The number of determiner plus noun combinations in connected speech increased for four speakers. These findings attest to the close relationship between frequently co-occurring content and function words, and indicate that intervention for word-finding deficits can profitably proceed beyond single word naming, to retrieval in appropriate syntactic contexts. We also examined the relationship between effects of therapy, and amount and intensity of therapy. We found no relationship between immediate effects and amount or intensity of therapy. However, those participants whose naming maintained at follow-up completed the therapy regime in fewer sessions, of relatively longer duration. We explore the relationship between therapy regime and outcomes, and propose future considerations for research.     

The Cambridge Semantic Memory Test Battery: Detection of semantic deficits in semantic dementia and Alzheimer's disease

Abstract

We report a case study of a patient (HR) with a large left temporal lesion who inserted spelled words, particularly nouns, into his fluent but otherwise empty spoken production. Although he generated neologisms in picture-naming and oral reading tasks, they did not appear in his spontaneous speech. Characteristics of his written production included the following: semantic errors; misspellings; frequency and word-length effects; and better performance for concrete nouns than for low-imageability nouns, verbs, function words, adjectives and adverbs. HR's attempts at writing sentences were agrammatic and notably lacking in verbs; he also performed poorly in generating sentences from printed sentence fragments. Although impaired in auditory rhyming tasks, his performance was superior to the detection of rhymes presented visually. HR's writing performance and the striking differences between his spoken and written output are similar to those of a number of patients previously reported. We note parallels between these patterns and the characteristics of cases where the processing and/or production of written words can be assigned to the right hemisphere.     

Case Study Impairment to phonological processes in a Cantonese‐speaking brain‐damaged patient

Background: Previous studies have shown that brain‐damaged patients with selective deficits to phonological processes produced frequent phonological errors and similar error patterns in all spoken tasks, exhibited the effects of word frequency, grammatical class, and imageability, and were unable to make rhyming judgements, due to impaired lexical retrieval and/or phonological representations. Aims: This paper describes a Cantonese‐speaking brain‐damaged patient, LKK, whose performance patterns in spoken tasks indicate impairment to both the lexically mediated non‐semantic and semantic pathways of oral production, as well as the phonological output buffer. Methods & Procedures: A range of tasks was conducted including repetition, reading aloud, oral naming, written/spoken word–picture matching, non‐verbal semantic tests, written lexical decision, and homophone judgements. Outcomes & Results: LKK performed normally on written lexical decision, word–picture matching, and non‐verbal semantic tests, but he was unable to make homophone judgements and showed impaired production in all oral tasks. He was better able to read aloud names of objects than to name them. He also made more semantic errors in naming than reading. His accuracy in reading single words was affected by word frequency and form class. Further observations of his oral production included better (but nevertheless impaired) performance on repetition than reading and naming, a consistent effect of word length across tasks, and a tendency for phonological errors to occur on the coda compared with the onset. Conclusions: There was sufficient evidence for deficits of the phonological lexicon and/or the access to it along the non‐semantic route and the semantic pathway at the post‐semantic level in LKK. The effect of word length and comparable patterns of error distribution across spoken tasks suggested additional impairment to the phonological output buffer. The different levels of accuracy in repetition, reading, and naming, as well as the differential rates of semantic errors in these tasks were consistent with predictions of the summation hypothesis.     

Semantic anomaly judgement in individuals with probable Alzheimer's disease

BACKGROUND: Research has shown that individuals with probable Alzheimer's disease (PrAD) show impaired semantic knowledge of nouns. More specifically, while they demonstrate preserved superordinate category information, information regarding specific semantic attributes associated with subordinates appears to be disrupted. Results of some recent studies suggest that PrAD participants may also be impaired in processing semantic information associated with verbs. AIMS: Provided that a parallel exists between PrAD participants' noun and verb impairment, it is plausible that the semantic deficits observed in the breakdown of their noun lexicon may also exist in their knowledge of verb-related information. This experiment examined PrAD participants' knowledge of the semantic restrictions associated with the complements of verbs. METHODS #ENTITYSTARTX00026; PROCEDURES: Fourteen PrAD participants were asked to judge the semantic plausibility of 44 auditorily presented sentences. To examine their knowledge of the selection restriction of verbs, each verb was paired with two plausible complements that fully met the restriction, an implausible complement that violated the specific attributes required but belonged to the correct semantic category, and an implausible complement that violated the semantic category requirement. OUTCOMES #ENTITYSTARTX00026; RESULTS: Results showed that PrAD participants' errors were primarily on anomalous sentences that contained implausible complements that belonged to the correct semantic category. CONCLUSIONS: This finding confirms our hypothesis and suggests that a parallel pattern exists in PrAD participants' breakdown in noun and verb knowledge.     

Semantic and syntactic processing of mass and count nouns: Data from dementia

In the present research, we investigated the processing of Italian mass and count nouns and of their semantic and morphosyntactic attributes in people with neurodegenerative disease. The performance of a group of 26 Italian participants with Alzheimer’s disease was studied in a semantic judgment task and a syntactic judgment task. Results were analyzed by means of mixed-effect models, revealing an interaction between task and stimulus category: The probability for correct responses to mass stimuli was significantly lower than that for count stimuli, but only in the semantic task. These findings confirm the major semantic impairment in dementia and suggest that mass nouns have particular features that make them more prone to impairment than count nouns for a progressively degenerating brain.     

Interplay between syntax and semantics during sentence comprehension: ERP effects of combining syntactic and semantic violations

This study investigated the effects of combined semantic and syntactic violations in relation to the effects of single semantic and single syntactic violations on language-related event-related brain potential (ERP) effects (N400 and P600/SPS). Syntactic violations consisted of a mismatch in grammatical gender or number features of the definite article and the noun in sentence-internal or sentence-final noun phrases (NPs). Semantic violations consisted of semantically implausible adjective-noun combinations in the same NPs. Combined syntactic and semantic violations were a summation of these two respective violation types. ERPs were recorded while subjects read the sentences with the different types of violations and the correct control sentences. ERP effects were computed relative to ERPs elicited by the sentence-internal or sentence-final nouns. The size of the N400 effect to the semantic violation was increased by an additional syntactic violation (the syntactic boost). In contrast, the size of the P600/SPS to the syntactic violation was not affected by an additional semantic violation. This suggests that in the absence of syntactic ambiguity, the assignment of syntactic structure is independent of semantic context. However, semantic integration is influenced by syntactic processing. In the sentence-final position, additional global processing consequences were obtained as a result of earlier violations in the sentence. The resulting increase in the N400 amplitude to sentence-final words was independent of the nature of the violation. A speeded anomaly detection task revealed that it takes substantially longer to detect semantic than syntactic anomalies. These results are discussed in relation to the latency and processing characteristics of the N400 and P600/SPS effects. Overall, the results reveal an asymmetry in the interplay between syntax and semantics during on-line sentence comprehension.     

An investigation of semantic errors in unimpaired and Alzheimer's speakers of Italian

Semantic errors are a common type of slip of the tongue for normal speakers; they are also considered to be the hallmark of progressive diseases that affect semantic memory such as Alzheimer's Disease (AD) and semantic dementia. In unimpaired speakers, semantic errors have been shown to be affected by syntactic variables. For example, Marx (1999) has shown that speakers of a gendered language such as German tend to substitute a target with another word that shares the same grammatical gender with the target more often than chance would predict. This finding suggests that errors occur at a level at which lexical information about the target is activated and retrieved. Here, we assess whether such an effect of syntactic variables (gender) also holds in experimental tasks designed to induce errors in unimpaired speakers of Italian (another gendered language) and whether this effect can also be observed in the semantic errors produced in the same task by AD patients. We found that for the unimpaired speakers, the gender of the target word constrained the error committed, while this was not the case for the AD patients. We take this finding to suggest a different locus for the errors in the two populations: while the semantic errors by the unimpaired speakers occur because of mis-selection of a lexical entry due to lexical competition among semantically similar words, the errors by the AD patients occur because of insufficient activation of lexical representations.     

Grammatical dissociation during acquired childhood aphasia

Aim  We report the case of a 6-year-old female who suffered a left hemisphere stroke attributed to a genetically determined prothrombotic state. She presented a fluent speech pattern with selective difficulty in retrieving names but not verbs. An evaluation was designed to clarify whether her symptoms represented a specific impairment of name retrieval.
Method  The child undertook an experimental battery of visual naming tasks requiring the production of 52 nouns (belonging to nine different semantic categories) and 44 verbs. Her performance was compared with that of 12 healthy children, matched for age and IQ, attending a local kindergarten.
Results  The child retrieved significantly more verbs than nouns ( χ ²=16.27, p <0.01) and had a significantly lower score in noun ( t =−7.2, p <0.005), but not in verb retrieval than the comparison group. This pattern persisted when verbs and nouns were matched for oral word frequency, showing that the results could not be explained by stimuli difficulty.
Interpretation  To our knowledge, this is the first report of a grammatical dissociation in a child. It suggests that nouns and verbs are subject to different processing early in development, at least before the formal acquisition of grammar. It contradicts theories that postulate a common processing of different grammatical categories early in life.