Word Retrieval Processes Research Articles

Long-term linguistic outcome in adults with congenital cytomegalovirus infection

Background Congenital cytomegalovirus (cCMV) is the most common prenatal infection and the main infectious cause of neurodevelopmental abnormalities in developed countries. Long-term neuropsychological outcome of cCMV infection is still not well understood. This is the first study that presents linguistic follow-up data performed on adults who were infected in utero. Method All individuals from a universal newborn CMV screening study in Sweden sampled from 1977 to 1985 were invited to participate in a follow-up study. 34/71 persons (48%) with cCMV and 22/46 controls (48%) were enrolled. Participants were between 34 and 43 years. Linguistic ability was evaluated with two-word fluency tasks (FAS letter fluency and verb fluency), and a qualitative analysis of the participants’ word retrieval strategies was conducted. Results No statistically significant group differences were found in the total number of retrieved words. When related to Swedish norm data, 43% of participants with cCMV infection, all asymptomatic at birth, had adequate results on both FAS and verb fluency tasks, compared to 86% of the controls. Education level was the most important factor for word fluency ability in both groups. Adults with cCMV infection and higher education levels used less effective retrieval strategies on FAS letter fluency than controls. Conclusion This study suggests that adults with cCMV infection may have deficits in the word retrieval process, even in the absence of known neurodevelopmental disorders. Long-term effects of cCMV infection may exist even in those with asymptomatic infection at birth.

Focusing on the locus of the breakdown for treatment of anomia: a pilot study

ABSTRACT The primary goal of this study was to evaluate the treatment effects of semantic feature analysis (SFA) and phonological components analysis (PCA) on word retrieval processing in persons with aphasia (PWAs). After identifying the locus of the breakdown in lexical retrieval processing, 15 monolingual native Persian speakers with aphasia were divided into two groups. After three naming trials, participants with dominant semantic deficits received SFA, and participants with primary phonological deficits were provided with PCA three times a week for eight weeks. Both approaches improved participants’ naming and performance on language tests, including spontaneous speech, repetition, comprehension, and semantic processing. However, the correct naming of treated and untreated items was higher in mild-to-moderate participants, with mostly circumlocution and semantic paraphasias in the SFA group. The same holds for mild-to-moderate participants with mostly phonemic paraphasia who received PCA therapy. Moreover, the results showed that participants’ baseline naming performance and semantic abilities could be associated with the treatment outcomes. Although limited by a lack of a control group, this study provided evidence supporting the possible benefits of focusing on the locus of the breakdown for treating anomia through SFA and PCA approaches, specifically in participants with mild to moderate aphasia. However, for those with severe aphasia, the treatment choice may not be as straightforward because several variables are likely to contribute to this population’s word-finding difficulties. Replication with larger, well-stratified samples, use of a within-subjects alternating treatment design and consideration of treatments’ long-term effects are required to better ascertain the effects of focusing on the locus of breakdown for treatment of anomia.

Phonological Priming in Children with Developmental Language Disorder

<p>本研究利用跨模式圖字干擾作業探討與比較習華語發展性語言障礙兒童(DLD)和典型發展兒童(TD)在音節、聲調與次音節單位（聲母及韻母）的音韻促發效應，以更深入了解兒童音韻表徵的型態及處理歷程。共有16名4至6歲11個月的DLD兒童和16名與其性別和年齡配對的TD兒童。促發項之音韻類型包括同音節、同聲母、同韻母、同聲調及無關項；促發項相對於目標項所呈現的時間為前150毫秒(SOA -150)、同時(SOA 0)及後150毫秒(SOA +150)。研究結果指出：(1)TD兒童的反應速度和正確率優於DLD兒童；(2)兩組兒童皆呈現同音節促進效應，且均無同聲調促進效應，代表華語兒童詞彙提取歷程中已具有音節框架的存在，而聲調對於詞彙提取的貢獻有限；(3)兩組主要的差異在次音節單位，DLD兒童在SOA -150和SOA +150時均呈現同韻母促進效應，而TD兒童僅在SOA 0呈現同聲母抑制效應。據此推論DLD兒童在次音節單位的處理方式與TD兒童不同，TD兒童可能是採用Cohort model的處理模式，而DLD兒童則未使用或尚未發展成熟到能使用此處理模式，其依賴語音知覺顯著性較高的韻母協助詞彙提取。整體而言，DLD兒童音韻處理歷程較無效率，顯現出詞彙提取困難。綜上推論，建議教學與臨床治療需重視DLD兒童詞彙提取與音韻處理能力之評估與訓練。</p> <p> </p><p>Phonological priming with cross-modal picture-word interference task was used to in-vestigate the phonological processing in children with and without developmental language disorder (DLD). Sixteen children with DLD aged 4 to 6 years and 11 months, and 16 gender- and age-matched children with typical development (TD) were recruited. The target words were paired with 6 types of phonological primes (identical, syllable-related, onset-related, rhyme-related, tone-related, unrelated), and primes were presented 150ms before (SOA -150), simultaneously (SOA 0), or 150ms after (SOA +150) the target. Results showed that (1) the TD group performed faster and more accurately than the DLD group; (2) both groups demonstrated syllable priming and lack tone priming at all SOAs, which suggests children selected a syllable frame in the lexical access process and the contribution of tone is limited; (3) the primary differences between these two groups were at sub-syllabic level. The DLD group exhibited rhyme priming at SOA -150 and SOA +150, while the TD group only ex-hibited onset interference at SOA 0. Based on these results, the possible inference was that children with TD may apply Cohort model to perceive incoming phonological information, however, children with DLD may not utilize this manner or they were not mature enough to use it, and their word retrieval process depended on high-saliency rhyme. Overall, the phonological processing in children with DLD was inefficient, and they revealed word re-trieval difficulty. Thus, it is recommended to evaluate and intervene word retrieval and phonological processing in children with DLD.</p> <p> </p>

Picture-Word Interference Effects Are Robust With Covert Retrieval, With and Without Gamification.

The picture-word interference (PWI) paradigm has been used to investigate the time course of processes involved in word retrieval, but is challenging to implement online due to dependence on measurements of vocal reaction time. We performed a series of four experiments to examine picture-word interference and facilitation effects in a form of covert picture naming, with and without gamification. A target picture was accompanied by an audio word distractor that was either unrelated, phonologically-related, associatively-related, or categorically-related to the picture. Participants were instructed to judge whether the name of the target picture ended in the phoneme assigned to the block by pressing corresponding keys as quickly and accurately as possible. Experiments 1 and 2 successfully replicated categorical interference and phonological facilitation effects at different optimal stimulus-onset-asynchronies (SOAs) between words and pictures. Experiment 3 demonstrated that a key gamification feature (collecting coins) motivated faster speed at the expense of accuracy in the gamified vs. experimental format of the task. Experiment 4 adopted the optimal SOAs and verified that the gamification reveals expected interference and facilitation effects despite the speed-accuracy tradeoff. These studies confirmed that categorical interference occurs earlier than phonological facilitation, while both processes are independent from articulation and inherent to word retrieval itself. The covert PWI paradigm and its gamification have methodological value for neuroimaging studies in which articulatory artifacts obscure word retrieval processes, and may be developed into potential online word-finding assessments that can reveal word retrieval difficulties with greater sensitivity.

The tip-of-the-tongue phenomenon in older adults with subjective memory complaints.

In older adults with subjective memory complaints (SMCs), featuring a decline in memory but not exhibiting problems during medical examinations and objective memory tests, the weak links between nodes evident in the word retrieval process can be a primary factor for predicting mild cognitive impairment and dementia. This study examined the frequency of the “Tip-of-the-Tongue” (ToT) phenomenon according to age and subjective memory complaints of older adults, and identified differences in the resolution method using sequential cues. A celebrity naming task was performed on older adults (aged 50 to 79) with SMCs (n = 30) and without SMCs (n = 30), comparing the frequency of the ToT phenomenon and in resolution methods. We found that, even if our subjects with SMCs obtained normal results in the objective neuropsychology test, they experienced a significantly higher frequency of the ToT phenomenon than those without SMCs. In addition, subjects with SMCs showed a significantly lower rate of resolution, both spontaneous and following a syllabic cue, compared to those without SMCs. SMCs can be a very early marker of degenerative diseases causing cognitive dysfunction, and thus the selection of appropriate tools for early detection of SMCs is important. The proper naming task may sensitively detect subclinical symptoms of SMCs in subjects who are not classified as patients with cognitive impairments on general neuropsychological test. In addition, this task can identify weak connections between semantic and phonological nodes due to changes in the neural region of older adults with SMCs.

Quantifying the Interplay of Semantics and Phonology During Failures of Word Retrieval by People With Aphasia Using a Multiplex Lexical Network.

Investigating instances where lexical selection fails can lead to deeper insights into the cognitive machinery and architecture supporting successful word retrieval and speech production. In this paper, we used a multiplex lexical network approach that combines semantic and phonological similarities among words to model the structure of the mental lexicon. Network measures at different levels of analysis (degree, network distance, and closeness centrality) were used to investigate the influence of network structure on picture naming accuracy and errors by people with Anomic, Broca's, Conduction, and Wernicke's aphasia. Our results reveal that word retrieval is influenced by the multiplex lexical network structure in at least two ways-(a) the accuracy of production and error type on incorrect productions were influenced by the degree and closeness centrality of the target word, and (b) error type also varied in terms of network distance between the target word and produced error word. Taken together, the analyses demonstrate that network science techniques, particularly the use of the multiplex lexical network to simultaneously represent semantic and phonological relationships among words, reveal how the structure of the mental lexicon influences language processes beyond traditionally examined psycholinguistic variables. We propose a framework for how the multiplex lexical network approach allows for understanding the influence of mental lexicon structure on word retrieval processes, with an eye toward a better understanding of the nature of clinical impairments, like aphasia.

A comparison of drawing and writing on facilitating word retrieval in individuals with aphasia

ABSTRACTBackground: Drawing has long been a focus in aphasia research as a compensatory strategy for improving functional communication in individuals with aphasia, but fewer studies have addressed drawing as a facilitative tool to improve their verbal output.Aims: The purpose of the current study was to investigate differences in naming accuracy in individuals with aphasia during a drawing versus a writing condition. Two research questions were formed to examine the role of drawing in facilitating naming: 1) Will participants perform better when naming with drawing compared to confrontation naming only or when naming with writing? and 2) Is the quality of the picture drawn related to the naming accuracy?Methods & Procedures: Across three separate one-hour sessions, fifteen individuals with aphasia (n = 15) aged 44–81 years (M = 61.47, SD = 13.27) were evaluated using two standardized language assessments, the Western Aphasia Battery-Revised and Pyramid and Palm Tree Test, and three naming tasks designed to assess the effect of writing and drawing on naming performance. The three naming conditions consisted of confrontation naming only, naming with drawing, and naming with writing.Outcomes & Results: A one-way, repeated measures analysis of variance (ANOVA) was computed to analyze the impact of naming conditions on the participants’ naming accuracy. The main effect of naming conditions was statistically significant, F (1, 14) = 5.87, p < 0.05, and Bonferroni correction revealed that the participants performed significantly better in the naming with drawing condition than with writing condition. In addition, no correlation between the quality of the pictures drawn and the participants’ naming performance was found which suggested that the quality of drawing did not affect the accuracy of naming.Conclusions: When attempting to name a picture along with drawing its representation, the act of drawing may facilitate word retrieval by stimulating the semantic network associated with the word and involving the right cerebral hemisphere in the word retrieval process. Through drawing, these semantic features of the target word are more strongly activated than other related words. When the semantic features are more strongly activated, the probabilities of retrieving the target word may increase. In contrast, writing heavily relies on the left hemisphere and linguistic systems. Thus, naming when attempting to write the associated word may be a more cognitively and linguistically demanding task for individuals with aphasia.

The Study of Language in the Amyotrophic Lateral Sclerosis - Frontotemporal Spectrum Disorder: a Systematic Review of Findings and New Perspectives.

Amyotrophic Lateral Sclerosis is a neurodegenerative disorder characterized primarily by motor network disruption. Extra-motor manifestations including executive functions, social cognition, and behavioral changes are now well recognized as important features of ALS, and are associated with frontotemporal and frontostriatal network disruption. However, the presence and characterization of language changes has received less attention. This systematic review characterizes the profile of reported language dysfunction in ALS. PRISMA guidelines were implemented to carry out and report the review. Current evidence suggests that areas of neuroanatomical disruption in ALS spread to language centers such as posterior, inferior frontal and superior temporal areas leading to deficits in word retrieval, syntactic and grammatical processing, and spelling. However, the majority of studies of language in ALS have been limited by the recruitment of small clinic-based prevalent samples and important questions remain regarding the incidence and progression of language impairment in ALS. Further studies from population-based incident cohorts will help to determine the range of language deficits in ALS, and how these relate to previously defined executive and behavioral sub-phenotypes.

How does language change after an intensive treatment on imitation?

ABSTRACTThe main aim of our study was to investigate the role of imitation in improving word-finding difficulties in a group of aphasic subjects. For this purpose, we designed software based on the computerised program described by Lee et al. (2010). Seven subjects with aphasia resulting from a brain injury were enrolled in the study. A battery of tests was administered to participants one month before the treatment (T0) and immediately before its beginning (T1) with the aim of detecting their language difficulties. In the period between T0 and T1 sessions, participants underwent traditional logopaedic and neuropsychological rehabilitation. The treatment lasted 45 days with 90-minute sessions per day and it was personalised in terms of difficulty for each of the subjects. During every session the task required participants to carefully observe and then imitate six actors while pronouncing aloud a series of words and sentences describing a set of items. The results showed a significant improvement in the whole sample and in all the analysed measures only between T1 and T2 (post-training evaluation), while, as expected, no improvement was registered between T0 and T1. Such outcomes are consistent with research showing the key role played by imitation in the word retrieval process following aphasia.

Lesion evidence for a critical role of left posterior but not frontal areas in alpha-beta power decreases during context-driven word production.

Different frequency bands in the electroencephalogram are postulated to support distinct language functions. Studies have suggested that alpha-beta power decreases may index word-retrieval processes. In context-driven word retrieval, participants hear lead-in sentences that either constrain the final word ('He locked the door with the') or not ('She walked in here with the'). The last word is shown as a picture to be named. Previous studies have consistently found alpha-beta power decreases prior to picture onset for constrained relative to unconstrained sentences, localised to the left lateral-temporal and lateral-frontal lobes. However, the relative contribution of temporal versus frontal areas to alpha-beta power decreases is unknown. We recorded the electroencephalogram from patients with stroke lesions encompassing the left lateral-temporal and inferior-parietal regions or left-lateral frontal lobe and from matched controls. Individual participant analyses revealed a behavioural sentence context facilitation effect in all participants, except for in the two patients with extensive lesions to temporal and inferior parietal lobes. We replicated the alpha-beta power decreases prior to picture onset in all participants, except for in the two same patients with extensive posterior lesions. Thus, whereas posterior lesions eliminated the behavioural and oscillatory context effect, frontal lesions did not. Hierarchical clustering analyses of all patients' lesion profiles, and behavioural and electrophysiological effects identified those two patients as having a unique combination of lesion distribution and context effects. These results indicate a critical role for the left lateral-temporal and inferior parietal lobes, but not frontal cortex, in generating the alpha-beta power decreases underlying context-driven word production.

P.4.f.004 - Interaction between word retrieval processing and affect in patients with obsessive compulsive disorder

P.4.f.004 - Interaction between word retrieval processing and affect in patients with obsessive compulsive disorder

Spatiotemporal dynamics of word retrieval in speech production revealed by cortical high-frequency band activity

Word retrieval is core to language production and relies on complementary processes: the rapid activation of lexical and conceptual representations and word selection, which chooses the correct word among semantically related competitors. Lexical and conceptual activation is measured by semantic priming. In contrast, word selection is indexed by semantic interference and is hampered in semantically homogeneous (HOM) contexts. We examined the spatiotemporal dynamics of these complementary processes in a picture naming task with blocks of semantically heterogeneous (HET) or HOM stimuli. We used electrocorticography data obtained from frontal and temporal cortices, permitting detailed spatiotemporal analysis of word retrieval processes. A semantic interference effect was observed with naming latencies longer in HOM versus HET blocks. Cortical response strength as indexed by high-frequency band (HFB) activity (70-150 Hz) amplitude revealed effects linked to lexical-semantic activation and word selection observed in widespread regions of the cortical mantle. Depending on the subsecond timing and cortical region, HFB indexed semantic interference (i.e., more activity in HOM than HET blocks) or semantic priming effects (i.e., more activity in HET than HOM blocks). These effects overlapped in time and space in the left posterior inferior temporal gyrus and the left prefrontal cortex. The data do not support a modular view of word retrieval in speech production but rather support substantial overlap of lexical-semantic activation and word selection mechanisms in the brain.

Right hemisphere structural adaptation and changing language skills years after left hemisphere stroke.

Stroke survivors with acquired language deficits are commonly thought to reach a 'plateau' within a year of stroke onset, after which their residual language skills will remain stable. Nevertheless, there have been reports of patients who appear to recover over years. Here, we analysed longitudinal change in 28 left-hemisphere stroke patients, each more than a year post-stroke when first assessed-testing each patient's spoken object naming skills and acquiring structural brain scans twice. Some of the patients appeared to improve over time while others declined; both directions of change were associated with, and predictable given, structural adaptation in the intact right hemisphere of the brain. Contrary to the prevailing view that these patients' language skills are stable, these results imply that real change continues over years. The strongest brain-behaviour associations (the 'peak clusters') were in the anterior temporal lobe and the precentral gyrus. Using functional magnetic resonance imaging, we confirmed that both regions are actively involved when neurologically normal control subjects name visually presented objects, but neither appeared to be involved when the same participants used a finger press to make semantic association decisions on the same stimuli. This suggests that these regions serve word-retrieval or articulatory functions in the undamaged brain. We teased these interpretations apart by reference to change in other tasks. Consistent with the claim that the real change is occurring here, change in spoken object naming was correlated with change in two other similar tasks, spoken action naming and written object naming, each of which was independently associated with structural adaptation in similar (overlapping) right hemisphere regions. Change in written object naming, which requires word-retrieval but not articulation, was also significantly more correlated with both (i) change in spoken object naming; and (ii) structural adaptation in the two peak clusters, than was change in another task-auditory word repetition-which requires articulation but not word retrieval. This suggests that the changes in spoken object naming reflected variation at the level of word-retrieval processes. Surprisingly, given their qualitatively similar activation profiles, hypertrophy in the anterior temporal region was associated with improving behaviour, while hypertrophy in the precentral gyrus was associated with declining behaviour. We predict that either or both of these regions might be fruitful targets for neural stimulation studies (suppressing the precentral region and/or enhancing the anterior temporal region), aiming to encourage recovery or arrest decline even years after stroke occurs.

Facilitation effects of cueing techniques in two Sesotho speakers with anomia

Aphasiologists developing treatments for anomia should closely align therapy methods with the typological and morphological characteristics of the language in question. The lead author initiated this study to develop more defensible interventions for speakers of Sesotho, a South African language. Prefix-based cueing (our alternative name for initial phoneme cueing that describes these cues in Sesotho-oriented terms) was compared to a novel technique, root-based cueing (RBC). While prefix-based cues are described in the literature, we hypothesized root-based cues would be more appropriate in this context since they were thought to be more consonant with the linguistic parameters of Sesotho. Two speakers with aphasia, who demonstrated significant anomic symptoms, served as participants. We used a multiple-baseline, single case study design. Two 144-item word lists were developed with every item represented by a photograph. Each of the two word lists was associated with one of the two cueing techniques investigated. After baseline measurements were obtained, each participant attended eight facilitation sessions for each cueing condition, resulting in eight data points per condition and participant. For both participants, RBC resulted in greater naming performance than cueing by means of initial phonemes. Our explanation of these results is based on the Interactive Lexical Network model of lexical access; root-based cues may be more effective because they more efficiently constrain the number of lemmas activated after a cue is provided. We argue that a confluence of factors (word-retrieval processes and the character of Sesotho morphosyntax) gave rise to the noted differences in naming facilitation.

Treatment of spoken and written word retrieval in primary progressive aphasia

Treatment of spoken and written word retrieval in primary progressive aphasia

Measuring word retrieval deficits in a multilingual child with SLI: Is there a better language?

Abstract Lexical word retrieval was examined in a single case study of a multilingual child (I.S.) with specific language impairment (SLI) for Bulgarian, English, and Greek, guided by theory-driven conceptualizations of the multilingual lexicon and word retrieval processing. An equivalent picture naming task was used across languages. Word retrieval impairments were measured in relation to lexical factors of the target words and participant variables. The data were then compared to three groups of children: two groups of multilingual peers with typical language development (TLD), age-matched (n = 6) and language-matched (n = 6), and a group of children with SLI without a multilingual background (n = 6). The results revealed that the lexical retrieval deficit manifested itself in all three languages. These findings strengthen previous claims that lexical retrieval deficits are comparable across languages and could potentially serve as a non-language specific clinical marker across different languages: Both storage and retrieval processes are assumed to underlie deficits retrieving words. Implications for vocabulary instruction in the multilingual classroom setting are discussed.

The enigmatic linguistic cerebellum: clinical relevance and unanswered questions on nonmotor speech and language deficits in cerebellar disorders.

Clinical case descriptions and experimental evidence dating back to the early part of the 19th century from time to time documented a range of nonmotor cognitive and affective impairments following cerebellar pathology. However, a causal relationship between disruption of nonmotor cognitive and affective skills and cerebellar disease was dismissed for several decades and the classical view of the cerebellum as a mere coordinator of autonomic and somatic sensorimotor function prevailed for more than two centuries in behavioural neuroscience. The ignorance of early clinical evidence suggesting a much richer and complex role for the cerebellum than a pure sensorimotor one is remarkable given that in addition: 1) the cerebellum contains more neurons than the rest of the combined cerebral cortex and 2) no other structure has as many connections with other parts of the brain as the cerebellum. During the past decades, the long-standing view of the cerebellum as pure coordinator of sensorimotor function has been substantially modified. From the late 1970s onwards, major advances were made in elucidating the many functional neuroanatomical connections of the cerebellum with the supratentorial association cortices that subserve nonmotor language, cognition and affect. Combined with evidence derived from experimental functional neuroimaging studies in healthy subjects and neurophysiological and neuropsychological research in patients, the role of the cerebellum has been substantially extended to include that of a crucial modulator of cognitive and affective processes. In addition to its long-established role in coordinating motor aspects of speech production, clinical and experimental studies with patients suffering from etiologically different cerebellar disorders have identified involvement of the cerebellum in a variety of nonmotor language functions, including motor speech planning, language dynamics and verbal fluency, phonological and semantic word retrieval, expressive and receptive syntax processing, various aspects of reading and writing and aphasia-like phenomena. Despite considerable efforts currently devoted to further refine typology and anatomoclinical configurations of nonmotor linguistic dysfunctions linked to cerebellar pathology, the exact underlying pathophysiological mechanisms of cerebellar involvement remain to be elucidated.

Effects of phonological neighbourhood on the treatment of naming in aphasia

Background: Phonological treatments to improve naming ability in aphasia focus on re-strengthening connections within the phonological system. Nonetheless, the efficacy of phonological treatments is still being explored with particular consideration of cognitive neuropsychological perspectives. Clinicians may also need to consider lexical factors that interact with the word retrieval process. Researchers have shown that phonological neighbourhood density influences normal language recognition and production, but limited evidence exists for how phonological neighbourhoods may affect the treatment of word retrieval deficits in individuals with aphasia.Aims: The present study explored if manipulating the emphasis on phonological neighbourhood during treatment has an effect on naming ability, particularly in an individual with predominantly phonologically based deficits. We hypothesised that training front- and end-matched words in a condition that emphasised phonological neighbourhood would result in greater naming improvements than training front- and end-matched words in a condition that does not emphasise neighbourhood.Methods & Procedures: In this case study, participant AH had a moderate phonologically based word naming deficit following a stroke. He produced phonemic paraphasias and neologisms in spontaneous speech and other spoken word production tasks. In treatment, AH was asked to name triplets of pictures of items that were phonologically related, sharing initial or final phonemes, or unrelated. Items were from either high- or low-density phonological neighbourhoods. High-density items were trained largely in the context of neighbours, therefore emphasising neighbourhood. Low-density items were not trained within a condition that emphasise neighbourhood. The treatment was administered for 9 weeks (27 sessions), with each condition, front-matched, end-matched and unrelated, trained for 8 consecutive sessions. AH’s naming accuracy on training words was assessed using a basic withdrawal design with three probe naming tests during the treatment phase and at 1-month post-therapy. Naming accuracy was also recorded during treatment sessions.Outcomes & Results: Front-matched words, in a condition that emphasises phonological neighbourhoods, had the greatest treatment effects, with a medium effect size when comparing pre- versus post-measures. A small treatment effect was observed for front-matched items where neighbourhood was not emphasised.Conclusions: Results suggest that front-matched triplets trained within a condition that emphasises phonological neighbourhoods may lead to the greatest treatment effect. Clinicians should be aware that stimulus parameters, such as phonological neighbourhood, may interact with the effectiveness of treatment protocols.

Evidence of semantic clustering in letter-cued word retrieval

Letter-cued word fluency is conceptualized as a phonemically guided word retrieval process. Accordingly, word clusters typically are defined solely by their phonemic similarity. We investigated semantic clustering in two letter-cued (P and S) word fluency task performances by 315 healthy adults, each for 1 min. Singular value decomposition (SVD) and generalized topological overlap measure (GTOM) were applied to verbal outputs to conservatively extract clusters of high-frequency words. The results generally confirmed phonemic clustering. However, we also found considerable semantic/associative clusters of words (e.g., pen, pencil, and paper), and some words showed both phonemic and semantic associations within a single cluster (e.g., pair, pear, peach). We conclude that letter-cued fluency is not necessarily a purely phonemic word retrieval process. Strong automatic semantic activation mechanisms play an important role in letter-cued lexical retrieval. Theoretical conceptualizations of the word retrieval process with phonemic cues may also need to be reexamined in light of these analyses.

TOPOLOGICAL VERSUS DYNAMICAL ROBUSTNESS IN A LEXICAL NETWORK

Semantic memory is the cognitive system devoted to the storage of conceptual knowledge. Empirical semantic networks constructed from adult generated free word association data represent a good map for this system. Concepts, represented as words, link each other with a certain weight representing the strength of their relation. Everyday experience shows that word search and retrieval processes, which can be assimilated to traversals on a semantic network, provide fluent and coherent speech, i.e. are efficient and robust. Brain pathologies, such as Alzheimer's disease or schizophrenia, severely damage neural structures and associated capacities. Thus, semantic networks must also undergo disruption, but the question is how long cognitive processes, which depend on the underlying structures, can operate before collapsing. Interestingly, we find that degradation of the original structure has a dramatic impact on the topology of semantic network, whereas the dynamics upon it evidence much higher resilience. We define this problem in the framework of percolation theory.