Consequences of an inhibition deficit for word production and comprehension: Evidence from the semantic blocking paradigm

We investigated the semantic blocking effect in picture naming and word–picture matching for two nonfluent aphasic patients who show evidence of a deficit in inhibiting verbal representations (M.L. and B.Q.), one fluent aphasic patient (K.V.), and neurologically intact control participants. In two picture-naming tasks (Experiments 1A and 1B), M.L. and B.Q., relative to controls, showed a greatly exaggerated semantic blocking effect in naming latencies that increased dramatically across repeated presentations. On two corresponding word–picture matching tasks (Experiments 2A and 2B), both also showed an increasing semantic blocking effect, though the effects were not as large nor as consistent as those in naming. The fluent patient, K.V., showed a pattern like controls on both tasks. On an associated word–picture matching task, both M.L. and B.Q. showed results paralleling those of controls. The contrast between the production and comprehension patterns for M.L. and B.Q. supports the conclusion that their exaggerated blocking effect in production arises during lexical rather than semantic selection. We postulate that M.L.'s (and potentially B.Q.'s) production effect is due to difficulties in postselection inhibition, which results in overactivation of lexical representations. This overactivation is likely to be one source of their nonfluency in spontaneous speech.     

Evidence for a context-sensitive word retrieval disorder in a case of nonfluent aphasia

We describe a patient (BM) with nonfluent aphasia who presents with sparse, fragmented spontaneous speech but normal or near-normal performance on standard naming tasks. However, more detailed investigation revealed some unusual features to BM's naming: On a task involving repeated naming of a small set of targets, his performance degenerated when the targets were semantically blocked, particularly at fast rates of presentation. This semantic blocking effect was not observed in an analogous wordpicture matching task. Also, it was not present on a task where a set of words had to be named repeatedly in a fixed, predictable sequence. Finally, a fluent aphasic patient who presented with a classic "output" anomia failed to show the semantic blocking and predictability effects. It is suggested that BM suffers from a context-sensitive word retrieval disorder. The disorder is attributed to a difficulty in modulating activation within the lexical network. Implications for nonfluent aphasia, as well as for models of lexical retrieval, are discussed.     

Density pervades: an analysis of phonological neighbourhood density effects in aphasic speakers with different types of naming impairment

We investigated the influence of phonological neighbourhood density (PND) on the performance of aphasic speakers whose naming impairments differentially implicate phonological or semantic stages of lexical access. A word comes from a dense phonological neighbourhood if many words sound like it. Limited evidence suggests that higher density facilitates naming in aphasic speakers, as it does in healthy speakers. Using well-controlled stimuli, Experiment 1 confirmed the influence of PND on accuracy and phonological error rates in two aphasic speakers with phonological processing deficits. In Experiments 2 and 3, we extended the investigation to an aphasic speaker who is prone to semantic errors, indicating a semantic deficit and/or a deficit in the mapping from semantics to words. This individual had higher accuracy, and fewer semantic errors, in naming targets from high- than from low-density neighbourhoods. It is argued that the Results provide strong support for interactive approaches to lexical access, where reverberatory feedback between word- and phoneme-level lexical representations not only facilitates phonological level processes but also privileges the selection of a target word over its semantic competitors.     

LEXICALISATION IN SPEECH PRODUCTION: EVIDENCE FROM FORM RELATED WORD SUBSTITUTIONS IN APHASIA

One of the major empirical sources of theories of speech production are speech errors in normal speakers. Speech errors occurring during lexicalisation of a concept to be expressed can result in whole-word substitutions that are target related in form and/ or meaning or can appear as nonword productions (neologism). Similar error phenomena have been reported for aphasic patients. The present study describes the aphasic, HZ, who produced mainly form-related word substitutions and neologisms in several single-word processing tasks (picture naming, repetition, and reading aloud). In picture naming, meaning-related substitutions also occurred as well as substitutions that were related both in meaning and form (mixed errors). Three hypotheses of the origin of formal errors were tested: the full interactive activation hypothesis postulating meaning-form interactions, the lexical (form) retrieval hypothesis, and the post-lexical phonological encoding hypothesis. HZ's performance on repetition and reading aloud (tests showed no mixed errors and no effects of imageability and of target frequency on formal errors) failed to support the predictions of the first two hypotheses. However, the phonological encoding hypotheses (enriched by a comprehensionbased editor) could also not account for the data (e.g. for some task-specific asymmetries in the error pattern). Instead, an attempt is made to account for formal and mixed errors by construing word form encoding as an interactively organised component within a two-stage model of lexicalisation. Formal errors are traced back to interactions between lexical forms and sublexical phonological information during the second stage of lexicalisation. Mixed errors occur when lexical forms of the target's semantic competitors are involved in word form encoding.     

Grammatical category dissociation in multilingual aphasia

Word retrieval deficits for specific grammatical categories, such as verbs versus nouns, occur as a consequence of brain damage. Such deficits are informative about the nature of lexical organization in the human brain. This study examined retrieval of grammatical categories across three languages in a trilingual person with aphasia who spoke Arabic, French, and English. In order to delineate the nature of word production difficulty, comprehension was tested, and a variety of concomitant lexical–semantic variables were analysed. The patient demonstrated a consistent noun–verb dissociation in picture naming and narrative speech, with severely impaired production of verbs across all three languages. The cross-linguistically similar noun–verb dissociation, coupled with little evidence of semantic impairment, suggests that (a) the patient has a true “nonsemantic” grammatical category specific deficit, and (b) lexical organization in multilingual speakers shares grammatical class information between languages. The findings of this study contribute to our understanding of the architecture of lexical organization in bilinguals.     

An influence of syntactic and semantic variables on word form retrieval

We report the case of DPI, an aphasic patient who shows a phonological impairment in production that spares certain syntactic and semantic categories. On a picture naming task, he produces mostly phono-logical paraphasias, and the probability of producing a correct response depends on the frequency and length of the target word. This deficit occurs in the presence of spared ability to find the grammatical gender of the items that he cannot name, intact conceptual knowledge, and very good reading and word repetition. Therefore, we conclude that DPI's deficit is restricted to the phonological retrieval of a correctly selected lexical entry. However, production errors are not uniform across semantic and syntactic domains. Numerals and names of days and months are totally spared compared to matched controls. In addition, abstract nouns and verbs are significantly less affected than concrete nouns, even when variables affecting phonological retrieval (frequency, length, syllabic structure) are controlled for. This suggests that a functional organisation in terms of semantic and syntactic variables exists at the level of phonological retrieval. We discuss these findings in light of current models of speech production.     

Comparing Electrophysiological Correlates of Word Production in Immediate and Delayed Naming Through the Analysis of Word Age of Acquisition Effects

Most EEG studies analysing speech production with event related brain potential (ERP) have adopted silent metalinguistic tasks or delayed or tacit picture naming in order to avoid possible artefacts during motor preparation. A central issue in the interpretation of these results is whether the processes involved in those tasks are comparable to those involved in overt speech production. In the present study we addressed a methodological issue about the integration of stimulus-aligned and response-aligned ERPs in immediate overt picture naming in comparison to delayed production, coupled with a theoretical point on the effect of word Age of Acquisition (AoA). High density EEG recordings were used and waveform analyses and spatio-temporal segmentation were combined on stimulus-aligned and response-aligned ERPs. The same sequence and duration of topographic maps appeared in the immediate and delayed production until around 350 ms after picture onset, revealing similar encoding processes until the beginning of phonological encoding, but modulations linked to word AoA were only observed in the immediate production. Considering stimulus-aligned and response-aligned ERPs together allowed to identify that a stable topography starting around 350 ms lasts 30 ms longer for late-acquired than for early-acquired words. This difference falls within the time-window of phonological encoding and its modulation can be linked to the longer production latencies for late-acquired words.     

Age of acquisition and lexical processing in Aphasia: A case study

Abstract

This paper presents a single-case study of an aphasic patient, NP, whose lexical processing was affected by age of acquisition, such that words typically acquired early in life were processed with greater accuracy in spoken naming, written naming, and reading aloud than were later-acquired words. A combination of multiple regression and factorial designs was used in an effort to establish that age of acquisition, rather than word frequency or imageability (both factors with which age of acquisition is highly correlated), influenced success in speech production tasks. In addition to showing effects of age of acquisition on spoken naming, written naming, and reading aloud, NP also showed evidence of both semantic and phonological impairments. On the basis of NP's pattern of impairments and studies of the effects of age of acquisition on lexical processing in normal subjects, we propose that age of acquisition affects the process of retrieving phonological word-forms, with early-acquired phonological representations being more robust and less vulnerable to brain injury than are later-acquired representations.     

Semantic impairment with and without surface dyslexia: Implications for models of reading

The two best-developed computational models of reading aloud, the DRC model of Coltheart and colleagues and the connectionist attractor model of Plaut and colleagues, offer very different views about the degree to which semantic knowledge is involved in lexical processing, and hence make differing predictions about how semantic impairment (as seen, for example, in semantic dementia) will impact on lexical processing in clinical cases. Two cases meeting the criteria for semantic dementia, PC and EM, were given a battery of tests comprising comprehension tasks, a reading task, and a visual word recognition (lexical decision) task. All tasks used the same target words allowing cross-test and cross-patient comparisons. Both cases showed significant impairment of semantic memory, and word comprehension was found to be related to the word frequency of the target words. PC demonstrated poor reading of irregular words, with a surface dyslexic pattern of reading aloud, and he performed poorly on the visual lexical decision task. His ability to read irregular words was related to their frequency and to his ability to comprehend them. In contrast, his visual lexical decision performance was not reliably influenced by his comprehension of the same words or by their frequency. EM demonstrated essentially perfect reading aloud of irregular words and essentially perfect visual lexical decision, despite her severe semantic impairment. The pattern of performance shown by EM is consistent with the DRC model of reading, but inconsistent with the connectionist attractor model and with the view, associated with that model, that orthographic and phonological processes cannot remain intact when semantic representations are degraded.     

Semantic impairment with and without surface dyslexia: Implications for models of reading

The two best-developed computational models of reading aloud, the DRC model of Coltheart and colleagues and the connectionist attractor model of Plaut and colleagues, offer very different views about the degree to which semantic knowledge is involved in lexical processing, and hence make differing predictions about how semantic impairment (as seen, for example, in semantic dementia) will impact on lexical processing in clinical cases. Two cases meeting the criteria for semantic dementia, PC and EM, were given a battery of tests comprising comprehension tasks, a reading task, and a visual word recognition (lexical decision) task. All tasks used the same target words allowing cross-test and cross-patient comparisons. Both cases showed significant impairment of semantic memory, and word comprehension was found to be related to the word frequency of the target words. PC demonstrated poor reading of irregular words, with a surface dyslexic pattern of reading aloud, and he performed poorly on the visual lexical decision task. His ability to read irregular words was related to their frequency and to his ability to comprehend them. In contrast, his visual lexical decision performance was not reliably influenced by his comprehension of the same words or by their frequency. EM demonstrated essentially perfect reading aloud of irregular words and essentially perfect visual lexical decision, despite her severe semantic impairment. The pattern of performance shown by EM is consistent with the DRC model of reading, but inconsistent with the connectionist attractor model and with the view, associated with that model, that orthographic and phonological processes cannot remain intact when semantic representations are degraded.     

Action naming with impaired semantics: Neuropsychological evidencecontrasting naming and reading for objects and verbs

We contrast naming from pictures, and reading words, for objects and verbs (actions relating to the objects) in a patient with a large, posterior left-hemisphere lesion. We present evidence for spared picture naming for verbs relative to objects, whilst the opposite pattern of sparing occurred in reading. Objects were also spared relative to verbs in tasks requiring that written words be matched to either pictures or auditory words, in the presence of semantically related or unrelated distractors. We conclude that verb semantics were more impaired than semantic knowledge for objects, and that the better semantic knowledge for object names supported word reading. With pictures, however, action verb retrieval was maintained through a nonsemantic route from vision to action, or though preserved right-hemisphere “action semantics.”     

Action naming with impaired semantics: Neuropsychological evidencecontrasting naming and reading for objects and verbs

We contrast naming from pictures, and reading words, for objects and verbs (actions relating to the objects) in a patient with a large, posterior left-hemisphere lesion. We present evidence for spared picture naming for verbs relative to objects, whilst the opposite pattern of sparing occurred in reading. Objects were also spared relative to verbs in tasks requiring that written words be matched to either pictures or auditory words, in the presence of semantically related or unrelated distractors. We conclude that verb semantics were more impaired than semantic knowledge for objects, and that the better semantic knowledge for object names supported word reading. With pictures, however, action verb retrieval was maintained through a nonsemantic route from vision to action, or though preserved right-hemisphere "action semantics."     

AN INFLUENCE OF SYNTACTIC AND SEMANTIC VARIABLES ON WORD FORM RETRIEVAL

We report the case of DPI, an aphasic patient who shows a phonological impairment in production that spares certain syntactic and semantic categories. On a picture naming task, he produces mostly phono-logical paraphasias, and the probability of producing a correct response depends on the frequency and length of the target word. This deficit occurs in the presence of spared ability to find the grammatical gender of the items that he cannot name, intact conceptual knowledge, and very good reading and word repetition. Therefore, we conclude that DPI's deficit is restricted to the phonological retrieval of a correctly selected lexical entry. However, production errors are not uniform across semantic and syntactic domains. Numerals and names of days and months are totally spared compared to matched controls. In addition, abstract nouns and verbs are significantly less affected than concrete nouns, even when variables affecting phonological retrieval (frequency, length, syllabic structure) are controlled for. This suggests that a functional organisation in terms of semantic and syntactic variables exists at the level of phonological retrieval. We discuss these findings in light of current models of speech production.     

A single-system account of semantic and lexical deficits in five semantic dementia patients

In semantic dementia (SD), there is a correlation between performance on semantic tasks such as picture naming and lexical tasks such as reading aloud. However, there have been a few case reports of patients with spared reading despite profound semantic impairment. These reports have sparked an ongoing debate about how the brain processes conceptual versus lexical knowledge. One possibility is that there are two functionally distinct systems in the brain-one for semantic and one for lexical processing. Alternatively, there may be a single system involved in both. We present a computational investigation of the role of individual differences in explaining the relationship between naming and reading performance in five SD patients, among whom there are cases of both association and dissociation of deficits. We used a connectionist model where information from different modalities feeds into a single integrative layer. Our simulations successfully produced the overall relationship between reading and naming seen in SD and provided multiple fits for both association and dissociation data, suggesting that a single, cross-modal, integrative system is sufficient for both semantic and lexical tasks and that individual differences among patients are essential in accounting for variability in performance.     

A single-system account of semantic and lexical deficits in five semantic dementia patients

In semantic dementia (SD), there is a correlation between performance on semantic tasks such as picture naming and lexical tasks such as reading aloud. However, there have been a few case reports of patients with spared reading despite profound semantic impairment. These reports have sparked an ongoing debate about how the brain processes conceptual versus lexical knowledge. One possibility is that there are two functionally distinct systems in the brain—one for semantic and one for lexical processing. Alternatively, there may be a single system involved in both. We present a computational investigation of the role of individual differences in explaining the relationship between naming and reading performance in five SD patients, among whom there are cases of both association and dissociation of deficits. We used a connectionist model where information from different modalities feeds into a single integrative layer. Our simulations successfully produced the overall relationship between reading and naming seen in SD and provided multiple fits for both association and dissociation data, suggesting that a single, cross-modal, integrative system is sufficient for both semantic and lexical tasks and that individual differences among patients are essential in accounting for variability in performance.     

Word Meaning Blindness: A New Form of Acquired Dyslexia

We report the case of a patient, JO, who showed intact perception and comprehension of spoken words but who was impaired at accessing the meanings of words she was required to read silently. Letter recognition and written lexical decision were both intact, as was her reading aloud of both words and nonwords. JO's visual comprehension deficit suggests an impairment in mapping between representations in the visual input lexicon and the semantic system. This appears to be the counterpart in reading of “word meaning deafness” (a disorder of spoken word recognition in which patients can perceive spoken words and make auditory lexical decisions but have problems comprehending heard words, despite good comprehension of written words). Hence we refer to this new form of acquired dyslexia as “word meaning blindness.” JO's comprehension of words she read aloud was much better, presumably because recoding print into sound enabled her to use her preserved auditory comprehension processes to access meanings. She seemed unable, however, to use “inner speech” to access speech comprehension processes covertly, and further testing indicated a separate impairment of inner speech, which had the effect of making her word meaning blindness more apparent.     

White matter pathway supporting phonological encoding in speech production: a multi-modal imaging study of brain damage patients

In speech production, an important step before motor programming is the retrieval and encoding of the phonological elements of target words. It has been proposed that phonological encoding is supported by multiple regions in the left frontal, temporal and parietal regions and their underlying white matter, especially the left arcuate fasciculus (AF) or superior longitudinal fasciculus (SLF). It is unclear, however, whether the effects of AF/SLF are indeed related to phonological encoding for output and whether there are other white matter tracts that also contribute to this process. We comprehensively investigated the anatomical connectivity supporting phonological encoding in production by studying the relationship between the integrity of all major white matter tracts across the entire brain and phonological encoding deficits in a group of 69 patients with brain damage. The integrity of each white matter tract was measured both by the percentage of damaged voxels (structural imaging) and the mean fractional anisotropy value (diffusion tensor imaging). The phonological encoding deficits were assessed by various measures in two oral production tasks that involve phonological encoding: the percentage of nonword (phonological) errors in oral picture naming and the accuracy of word reading aloud with word comprehension ability regressed out. We found that the integrity of the left SLF in both the structural and diffusion tensor imaging measures consistently predicted the severity of phonological encoding impairment in the two phonological production tasks. Such effects of the left SLF on phonological production remained significant when a range of potential confounding factors were considered through partial correlation, including total lesion volume, demographic factors, lesions on phonological-relevant grey matter regions, or effects originating from the phonological perception or semantic processes. Our results therefore conclusively demonstrate the central role of the left SLF in phonological encoding in speech production.     

Selective impairment of semantics in lexical processing

Abstract

We report the performance of a neurologically impaired patient, KE, whose frequent errors in reading, writing, naming, and comprehension were nearly always semantically related to the target response. To quantify this pattern, a large number of items were presented for tasks of verbal and written naming, oral reading, writing to dictation, word/picture matching, and naming from tactile exploration. Detailed analyses of his performance on these tasks show very similar rates and types of errors, regardless of the modality of stimulus or response. KE's homogeneous pattern of semantic errors across modalities is interpreted as evidence for selective damage to a semantic system common to all lexical processes. In addition, although KE demonstrated some spared knowledge of all items in response to picture stimuli, we were able to interpret all aspects of his performance without resorting to a proposal that there are modality-specific semantic systems. Finally, we show that our interpretation, which assumes a unitary, modality-independent semantic system, can also account for previously reported cases in the cognitive neuropsychology literature that have been taken as evidence for modality-specific semantic systems.     

Electrophysiological characterization of facilitation and interference in the picture‐word interference paradigm

The picture‐word interference paradigm is often used to investigate the processes underlying word production. In this paradigm, participants name pictures while ignoring distractor words. The aim of this study is to investigate the processes underlying this task and how/when they differ from those involved in simple picture naming. It examines the electrophysiological signature of general interference (longer response times with than without distractors) and facilitation (shorter response times for distractor‐word stimuli overlapping in phonemes/orthography) effects. Mass univariate analyses are used to determine the temporal boundaries and spatial distribution of these effects without a priori restrictions in the time/space dimensions. Topographic pattern analyses complement this information by indicating whether (and when) the neural networks differ across conditions. Results suggest that the general interference effect has two loci, the grammatical encoding and the phonological encoding of the target word, with different neural networks involved in the two tasks during part of the grammatical encoding process. Furthermore, the electrophysiological signature of interference and facilitation effects in the time window of phonological encoding is highly similar, suggesting that the two effects could result from the same underlying mechanism. These findings are discussed in the light of existing accounts of interference and facilitation effects.     

Grammatical class and context effects in a case of pure anomia: Implications for models of language production

Numerous variables have been used in previous attempts to account for the performance of aphasic patients on naming tasks. These include lexical/semantic factors such as frequency, and contextual factors such as whether the target is produced as a single word or in a sentence. This paper reports the case of a pure anomic patient (HY) who was strongly affected by both lexical and contextual factors in his naming. Beyond a strong frequency effect, a marked grammatical class difference was noted. Verb production was far superior to noun production in single word naming. Production of nouns was highly facilitated by provision of a semantically relevant sentence frame. These two findings were related to current models of single word and sentence production; a functional locus for HY's naming deficit is proposed.