Dissociating the functional roles of arcuate fasciculus subtracts in speech production.

Recent tractography and microdissection studies have shown that the left arcuate fasciculus (AF)-a fiber tract thought to be crucial for speech production-consists of a minimum of 2 subtracts directly connecting the temporal and frontal cortex. These subtracts link the posterior superior temporal gyrus (STG) and middle temporal gyrus (MTG) to the inferior frontal gyrus. Although they have been hypothesized to mediate different functions in speech production, direct evidence for this hypothesis is lacking. To functionally segregate the 2 AF segments, we combined functional magnetic resonance imaging with diffusion-weighted imaging and probabilistic tractography using 2 prototypical speech production tasks, namely spoken pseudoword repetition (tapping sublexical phonological mapping) and verb generation (tapping lexical-semantic mapping). We observed that the repetition of spoken pseudowords is mediated by the subtract of STG, while generating an appropriate verb to a spoken noun is mediated by the subtract of MTG. Our findings provide strong evidence for a functional dissociation between the AF subtracts, namely a sublexical phonological mapping by the STG subtract and a lexical-semantic mapping by the MTG subtract. Our results contribute to the unraveling of a century-old controversy concerning the functional role in speech production of a major fiber tract involved in language.

Systematic Review and Meta-Analyses of Word Production Abilities in Dysfunction of the Basal Ganglia: Stroke, Small Vessel Disease, Parkinson's Disease, and Huntington's Disease.

Clinical populations with basal ganglia pathologies may present with language production impairments, which are often described in combination with comprehension measures or attributed to motor, memory, or processing-speed problems. In this systematic review and meta-analysis, we studied word production in four (vascular and non-vascular) pathologies of the basal ganglia: stroke affecting the basal ganglia, small vessel disease, Parkinson's disease, and Huntington's disease. We compared scores of these clinical populations with those of matched cognitively unimpaired adults on four well-established production tasks, namely picture naming, category fluency, letter fluency, and past-tense verb inflection. We conducted a systematic search in PubMed and PsycINFO with terms for basal ganglia structures, basal ganglia disorders and language production tasks. A total of 114 studies were included, containing results for one or more of the tasks of interest. For each pathology and task combination, effect sizes (Hedges' g) were extracted comparing patient versus control groups. For all four populations, performance was consistently worse than that of cognitively unimpaired adults across the four language production tasks (p-values < 0.010). Given that performance in picture naming and verb inflection across all pathologies was quantified in terms of accuracy, our results suggest that production impairments cannot be fully explained by motor or processing-speed deficits. Our review shows that while language production difficulties in these clinical populations are not negligible, more evidence is necessary to determine the exact mechanism that leads to these deficits and whether this mechanism is the same across different pathologies.

Attention for Speaking: Prestimulus Motor-cortical Alpha Power Predicts Picture Naming Latencies.

There is a range of variability in the speed with which a single speaker will produce the same word from one instance to another. Individual differences studies have shown that the speed of production and the ability to maintain attention are related. This study investigated whether fluctuations in production latencies can be explained by spontaneous fluctuations in speakers' attention just prior to initiating speech planning. A relationship between individuals' incidental attentional state and response performance is well attested in visual perception, with lower prestimulus alpha power associated with faster manual responses. Alpha is thought to have an inhibitory function: Low alpha power suggests less inhibition of a specific brain region, whereas high alpha power suggests more inhibition. Does the same relationship hold for cognitively demanding tasks such as word production? In this study, participants named pictures while EEG was recorded, with alpha power taken to index an individual's momentary attentional state. Participants' level of alpha power just prior to picture presentation and just prior to speech onset predicted subsequent naming latencies. Specifically, higher alpha power in the motor system resulted in faster speech initiation. Our results suggest that one index of a lapse of attention during speaking is reduced inhibition of motor-cortical regions: Decreased motor-cortical alpha power indicates reduced inhibition of this area while early stages of production planning unfold, which leads to increased interference from motor-cortical signals and longer naming latencies. This study shows that the language production system is not impermeable to the influence of attention.

Executive control in language production by children with and without language impairment.

BACKGROUND: Accumulating evidence suggests that the updating, inhibiting and shifting abilities underlying executive control are important for spoken language production in adults. However, little is known about this in children. AIMS: To examine whether children with and without language impairment differ in all or only some of these executive abilities, and whether they show corresponding differences when these abilities are engaged in language production. METHODS & PROCEDURES: Thirty-three children with specific language impairment (SLI) and 41 typically developing (TD) children (age matched, aged 8-12 years) completed standard executive control tests that measure the updating, inhibiting and shifting abilities. All children were native speakers of Dutch. Moreover, they performed a noun-phrase production task involving picture description within a picture-word interference paradigm. We measured their production accuracy and speed to assess length, distractor and switch effects, which reflect the updating, inhibiting and shifting abilities underlying executive control. OUTCOMES & RESULTS: Compared with TD children, the children with SLI had lower scores on all executive control tests. Moreover, they were overall slower and made more errors in the noun-phrase production task. Additionally, the magnitude of the distractor and switch effects was larger for the SLI than for the TD group. CONCLUSIONS & IMPLICATIONS: The results suggest that children with SLI have impaired language production and executive control abilities, and that some of the differences in the executive control abilities between SLI and TD groups were reflected in their language production.

Picture naming in typically developing and language-impaired children: the role of sustained attention.

BACKGROUND: Children with specific language impairment (SLI) have problems not only with language performance but also with sustained attention, which is the ability to maintain alertness over an extended period of time. Although there is consensus that this ability is impaired with respect to processing stimuli in the auditory perceptual modality, conflicting evidence exists concerning the visual modality. AIMS: To address the outstanding issue whether the impairment in sustained attention is limited to the auditory domain, or if it is domain-general. Furthermore, to test whether children's sustained attention ability relates to their word-production skills. METHODS & PROCEDURES: Groups of 7-9 year olds with SLI (N = 28) and typically developing (TD) children (N = 22) performed a picture-naming task and two sustained attention tasks, namely auditory and visual continuous performance tasks (CPTs). OUTCOMES & RESULTS: Children with SLI performed worse than TD children on picture naming and on both the auditory and visual CPTs. Moreover, performance on both the CPTs correlated with picture-naming latencies across developmental groups. CONCLUSIONS & IMPLICATIONS: These results provide evidence for a deficit in both auditory and visual sustained attention in children with SLI. Moreover, the study indicates there is a relationship between domain-general sustained attention and picture-naming performance in both TD and language-impaired children. Future studies should establish whether this relationship is causal. If attention influences language, training of sustained attention may improve language production in children from both developmental groups.

Beta oscillations reflect memory and motor aspects of spoken word production.

Two major components form the basis of spoken word production: the access of conceptual and lexical/phonological information in long-term memory, and motor preparation and execution of an articulatory program. Whereas the motor aspects of word production have been well characterized as reflected in alpha-beta desynchronization, the memory aspects have remained poorly understood. Using magnetoencephalography, we investigated the neurophysiological signature of not only motor but also memory aspects of spoken-word production. Participants named or judged pictures after reading sentences. To probe the involvement of the memory component, we manipulated sentence context. Sentence contexts were either constraining or nonconstraining toward the final word, presented as a picture. In the judgment task, participants indicated with a left-hand button press whether the picture was expected given the sentence. In the naming task, they named the picture. Naming and judgment were faster with constraining than nonconstraining contexts. Alpha-beta desynchronization was found for constraining relative to nonconstraining contexts pre-picture presentation. For the judgment task, beta desynchronization was observed in left posterior brain areas associated with conceptual processing and in right motor cortex. For the naming task, in addition to the same left posterior brain areas, beta desynchronization was found in left anterior and posterior temporal cortex (associated with memory aspects), left inferior frontal cortex, and bilateral ventral premotor cortex (associated with motor aspects). These results suggest that memory and motor components of spoken word production are reflected in overlapping brain oscillations in the beta band.

Simulation of impairment: Commentary on Nickels, Rapp, and Kohnen (2015).

Nickels, L., Rapp, B., and Kohnen, S. (2015. Challenges in the use of treatment to investigate cognition. Cognitive Neuropsychology, 32, 91-103) argue that impairment and treatment may be used to test computational models of cognition. They state that, contrary to their view, the authors of the WEAVER++ model of spoken word production have explicitly rejected simulation of impairment [i.e., Levelt, W. J. M., Roelofs, A., & Meyer, A. S. (1999b). Multiple perspectives on word production. Behavioral and Brain Sciences, 22, 61-69]. Here, I argue that this incorrectly characterizes the position of Levelt et al. Moreover, I further clarify this position, which holds that simulation of impairment requires both a theory of the intact system and assumptions about the underlying deficit, which is a widely accepted view. To demonstrate this position, I outline the approach taken in WEAVER++ simulations of aphasic performance reported in Roelofs, A. (2014. A dorsal-pathway account of aphasic language production: The WEAVER++/ARC model. Cortex, 59, 33-48). These simulations not only prove that the developers of WEAVER++ endorse simulation of impairment, but also highlight the importance of integrating psycholinguistic, functional neuroimaging, and tractographic evidence in testing models of impaired performance.

Domain-general inhibition areas of the brain are involved in language switching: fMRI evidence from trilingual speakers.

The prevailing theory of language switching states that unbalanced bilingual speakers use inhibition to switch between their languages (Inhibitory Control or IC model; Green, 1998). Using fMRI, we examined the brain mechanisms underlying language switching and investigated the role of domain-general inhibition areas such as the right inferior frontal gyrus (rIFG) and the pre-supplementary motor area (pre-SMA). Dutch-English-German trilinguals performed a picture naming task in the MRI scanner in both a blocked-language and a mixed-language context. The rIFG and pre-SMA showed more activation for switches to the second and third language (L2 and L3) compared to non-switch trials and blocked trials. No such difference was found for switches to the first language (L1). Our results indicate that language switching recruits brain areas related to domain-general inhibition. In this way, our study supports the claim that multilinguals use inhibition to switch between their languages.

Predicting naming latencies for action pictures: Dutch norms.

The present study provides Dutch norms for age of acquisition, familiarity, imageability, image agreement, visual complexity, word frequency, and word length (in syllables) for 124 line drawings of actions. Ratings were obtained from 117 Dutch participants. Word frequency was determined on the basis of the SUBTLEX-NL corpus (Keuleers, Brysbaert, & New, Behavior Research Methods, 42, 643-650, 2010). For 104 of the pictures, naming latencies and name agreement were determined in a separate naming experiment with 74 native speakers of Dutch. The Dutch norms closely corresponded to the norms for British English. Multiple regression analysis showed that age of acquisition, imageability, image agreement, visual complexity, and name agreement were significant predictors of naming latencies, whereas word frequency and word length were not. Combined with the results of a principal-component analysis, these findings suggest that variables influencing the processes of conceptual preparation and lexical selection affect latencies more strongly than do variables influencing word-form encoding.

Wernicke's functional neuroanatomy model of language turns 150: what became of its psychological reflex arcs?

Wernicke (Der aphasische Symptomencomplex: Eine psychologische Studie auf anatomischer Basis. Cohn und Weigert, Breslau.  https://wellcomecollection.org/works/dwv5w9rw , 1874) proposed a model of the functional neuroanatomy of spoken word repetition, production, and comprehension. At the heart of this epoch-making model are psychological reflex arcs underpinned by fiber tracts connecting sensory to motor areas. Here, I evaluate the central assumption of psychological reflex arcs in light of what we have learned about language in the brain during the past 150 years. I first describe Wernicke's 1874 model and the evidence he presented for it. Next, I discuss his updates of the model published in 1886 and posthumously in 1906. Although the model had an enormous immediate impact, it lost influence after the First World War. Unresolved issues included the anatomical underpinnings of the psychological reflex arcs, the role of auditory images in word production, and the sufficiency of psychological reflex arcs, which was questioned by Wundt (Grundzüge der physiologischen Psychologie. Engelmann, Leipzig. http://vlp.mpiwg-berlin.mpg.de/references?id=lit46 , 1874; Grundzüge der physiologischen Psychologie (Vol. 1, 5th ed.). Engelmann, Leipzig. http://vlp.mpiwg-berlin.mpg.de/references?id=lit806 , 1902). After a long dormant period, Wernicke's model was revived by Geschwind (Science 170:940-944. https://doi.org/10.1126/science.170.3961.940 , 1970; Selected papers on language and the brain. Reidel, Dordrecht, 1974), who proposed a version of it that differed in several important respects from Wernicke's original. Finally, I describe how new evidence from modern research has led to a novel view on language in the brain, supplementing contemporary equivalents of psychological reflex arcs by other mechanisms such as attentional control and assuming different neuroanatomical underpinnings. In support of this novel view, I report new analyses of patient data and computer simulations using the WEAVER++/ARC model (Roelofs 2014, 2022) that incorporates attentional control and integrates the new evidence.

Selective and nonselective inhibition of competitors in picture naming.

The present study examined the relation between nonselective inhibition and selective inhibition in picture naming performance. Nonselective inhibition refers to the ability to suppress any unwanted response, whereas selective inhibition refers to the ability to suppress specific competing responses. The degree of competition in picture naming was manipulated by presenting targets along with distractor words that could be semantically related (e.g., a picture of a dog combined with the word cat) or unrelated (tree) to the picture name. The mean naming response time (RT) was longer in the related than in the unrelated condition, reflecting semantic interference. Delta plot analyses showed that participants with small mean semantic interference effects employed selective inhibition more effectively than did participants with larger semantic interference effects. The participants were also tested on the stop-signal task, which taps nonselective inhibition. Their performance on this task was correlated with their mean naming RT but, importantly, not with the selective inhibition indexed by the delta plot analyses and the magnitude of the semantic interference effect. These results indicate that nonselective inhibition ability and selective inhibition of competitors in picture naming are separable to some extent.

Accounting for word production, comprehension, and repetition in semantic dementia, Alzheimer's dementia, and mild cognitive impairment.

It has been known since Pick (1892, 1904) that word retrieval is commonly impaired in left temporal lobe degeneration. Individuals with semantic dementia (SD), Alzheimer's dementia (AD), and mild cognitive impairment (MCI) present with word retrieval difficulty, while comprehension is less affected and repetition is preserved. Whereas computational models have elucidated performance in poststroke and progressive aphasias, including SD, simulations are lacking for AD and MCI. Here, the WEAVER++/ARC model, which has provided neurocognitive computational accounts of poststroke and progressive aphasias, is extended to AD and MCI. Assuming a loss of activation capacity in semantic memory in SD, AD, and MCI, the simulations showed that severity variation accounts for 99% of the variance in naming, comprehension, and repetition at the group level and 95% at the individual patient level (N = 49). Other plausible assumptions do less well. This supports a unified account of performance in SD, AD, and MCI.

Cerebral atrophy as a cause of aphasia: From Pick to the modern era.

In his epoch-making monograph, Wernicke (1874) claimed that atrophy of the brain cannot cause aphasia. Refuting this claim, Pick (1892, 1898, 1901, 1904a) documented in increasing detail several cases of aphasia with circumscribed atrophy of the left temporal lobe, frontal lobe, or both, which persuaded Wernicke (1906). To explain why the atrophy is circumscribed and leads to focal symptoms, Pick (1908a) advanced a functional network account. Behavioral, neuroanatomical, and histopathological studies by Dejerine and Sérieux, Fischer, Alzheimer, Altman, Gans, Onari and Spatz, and Stertz further illuminated the clinical syndromes, the exact spatial distributions of the atrophy, the underlying disease, and its laminar specificity. Unaware of these seminal studies, research from the 1970s until now has independently rediscovered all key findings, and also supports Pick's forgotten functional account of the distribution of atrophy and the focal symptoms. His frontal and temporal forms of aphasia foreshadowed what are now called the nonfluent/agrammatic and semantic variants of primary progressive aphasia. Moreover, aphasic symptoms may occur with frontal degeneration (what used to be called "Pick's disease") that yields personality changes and behavioral disturbances, now called the behavioral variant of frontotemporal dementia.

Word production and comprehension in frontotemporal degeneration: A neurocognitive computational Pickian account.

Over a century ago, Arnold Pick reported deterioration of word production and comprehension in frontotemporal degeneration, now a common finding. Individuals with semantic dementia (SD) and behavioral variant frontotemporal dementia (bvFTD) present with word retrieval difficulty, while their comprehension is less affected. Computational models have illuminated naming and comprehension in poststroke and progressive aphasias, including SD, but there are no simulations for bvFTD. Here, the WEAVER++/ARC model, previously applied to poststroke and progressive aphasias, is extended to bvFTD. Simulations tested the hypothesis of a loss of activation capacity in semantic memory in SD and bvFTD, caused by network atrophy (Pick, 1908a). The outcomes revealed that capacity loss explains 97% of the variance in naming and comprehension of 100 individual patients. Moreover, capacity loss correlates with individual ratings of atrophy in the left anterior temporal lobe. These results support a unified account of word production and comprehension in SD and bvFTD.

An fMRI study of inflectional encoding in spoken word production: Role of domain-general inhibition.

A major issue concerning inflectional encoding in spoken word production is whether or not regular forms (e.g., past tense walked) are encoded by rule application and irregular forms (e.g., swam) by retrieval from associative memory and inhibition of the regular rule. We used functional magnetic resonance imaging (fMRI) to examine the involvement of domain-general inhibition, thought to be underpinned by right inferior frontal gyrus (IFG), right pre-supplementary motor area (SMA), and right basal ganglia. Participants were presented with infinitive verbs that take either regular or irregular past tense. They switched between producing the past tense of these regular and irregular verbs in one block, and between inflecting or reading these infinitive verbs aloud in another block. As concerns corticobasal areas, compared to reading, inflecting activated left IFG and left preSMA/SMA. Regulars yielded higher activation than irregulars in these frontal areas, both on switch and repeat trials, which did not differ in activation. Switching between inflecting and reading activated left preSMA/SMA. These results indicate that inflectional encoding, and switching between inflecting and reading, engage frontal areas in the left hemisphere, including left preSMA/SMA for both and left IFG for inflecting, without recruiting the domain-general inhibition circuitry in the right hemisphere. We advance an account of inflectional encoding in spoken word production that assumes a distinction between regulars and irregulars, but without engaging domain-general inhibition.

Distractor strength and selective attention in picture-naming performance.

Whereas it has long been assumed that competition plays a role in lexical selection in word production (e.g., Levelt, Roelofs, & Meyer, 1999), recently Finkbeiner and Caramazza (2006) argued against the competition assumption on the basis of their observation that visible distractors yield semantic interference in picture naming, whereas masked distractors yield semantic facilitation. We examined an alternative account of these findings that preserves the competition assumption. According to this account, the interference and facilitation effects of distractor words reflect whether or not distractors are strong enough to exceed a threshold for entering the competition process. We report two experiments in which distractor strength was manipulated by means of coactivation and visibility. Naming performance was assessed in terms of mean response time (RT) and RT distributions. In Experiment 1, with low coactivation, semantic facilitation was obtained from clearly visible distractors, whereas poorly visible distractors yielded no semantic effect. In Experiment 2, with high coactivation, semantic interference was obtained from both clearly and poorly visible distractors. These findings support the competition threshold account of the polarity of semantic effects in naming.

A neurocognitive computational account of word production, comprehension, and repetition in primary progressive aphasia.

Computational models have elucidated word production, comprehension, and repetition in poststroke aphasia syndromes, but simulations are lacking for primary progressive aphasia (PPA) resulting from neurodegenerative disease. Here, the WEAVER++/ARC model, which has previously been applied to poststroke aphasia, is extended to the three major PPA variants: nonfluent/agrammatic, semantic, and logopenic. Following a seminal suggestion by Pick (1892/1977) and modern empirical insights, the model assumes that PPA arises from a progressive loss of activation capacity in portions of the language network with neurocognitive epicenters specific to each PPA variant. Computer simulations revealed that the model succeeds reasonably well in capturing the patterns of impaired and spared naming, comprehension, and repetition performance, at both group and individual patient levels. Moreover, it captures the worsening of performance with progression of the disease. The model explains about 90% of the variance, lending computational support to Pick's suggestion and modern insights.

The Diagnostic Value of Language Screening in Primary Progressive Aphasia: Validation and Application of the Sydney Language Battery.

PURPOSE: The three variants of primary progressive aphasia (PPA) differ in clinical presentation, underlying brain pathology, and clinical course, which stresses the need for early differentiation. However, brief cognitive tests that validly distinguish between all PPA variants are lacking. The Sydney Language Battery (SYDBAT) is a promising screening instrument that can be used as a first step in a comprehensive neuropsychological assessment to distinguish PPA subtypes, but evidence on its validity and reliability is to date limited. In the current study, the validation and diagnostic value of the SYDBAT are described for discriminating PPA subtypes as well as distinguishing PPA from mild cognitive impairment (MCI) or Alzheimer's dementia (AD). METHOD: Forty-five patients with PPA (13 with semantic PPA, 20 with logopenic PPA, and 12 with nonfluent/agrammatic PPA), 25 MCI patients, 13 AD patients, and 50 cognitively unimpaired controls were included in this study. Both patients and controls completed the SYDBAT-NL (Dutch version). Performance on and predictive ability of the four subtests (i.e., Naming, Word Comprehension, Repetition, and Semantic Association) were assessed. In addition, construct validity and internal consistency were examined. RESULTS: Different SYDBAT performance patterns were found across PPA and non-PPA patient groups. While a discriminant function analysis based on SYDBAT subtest scores could predict PPA subtype with 78% accuracy, it was more difficult to disentangle PPA from non-PPA patients based on SYDBAT scores alone. For assisting in clinical interpretation, simple rules were set up and translated into a diagnostic decision tree for subtyping PPA, which was capable of diagnosing a large proportion of the cases. Satisfying validity and reliability measures were found. CONCLUSIONS: The SYDBAT is an easy-to-use and promising screen for assessing single-word language processes, which may contribute to the differential diagnostic process of PPA and the assessment of language impairment in MCI and AD. It can be easily implemented for initial screening of patients in a memory clinic.

Attentional control in anterior cingulate cortex based on probabilistic cueing.

In Stroop-like tasks, conflict effects in behavioral measures and ACC activity are smaller on trials following an incongruent trial than following a congruent one. Researchers have found no agreement on whether these sequential effects in ACC can be driven by experienced incongruency only or also by expectations about target types. In the present fMRI experiment, we specifically manipulated the expectancies by using symbolic cues predicting with 75% or 50% certainty the incongruent or congruent targets in a Stroop-like task. Both behavioral and dorsal ACC data replicated previous sequential effects, with conflict effects being smallest for targets following the cues that predicted with 75% certainty the incongruent targets. However, these effects were not driven by experienced conflict but by symbolic cues. These results demonstrate differential attentional control activity in ACC after probabilistic cueing, providing evidence for control adjustments driven by changes in expectation.

How attention controls naming: Lessons from Wundt 2.0.

When models of the attentional control of vocal naming, applied to color-word Stroop and picture-word interference, were first computationally implemented and examined in 1990, an implementable model proposed by Wundt (1880, 1902) was not considered. Although these modern computer models, and more recent ones, clarify many aspects of the interference, most models fail to explain its time course, as outlined in Roelofs (2003). Wundt's (1902) model assigns a key role to top-down inhibition, which is absent in most of the modern models. Here, an implementation of his model is presented, called Wundt 2.0. The necessity of perceptual inhibition was demonstrated by computer simulations of the interference and its time course, and supported by existing evidence from oscillatory brain activity in the alpha frequency band. Moreover, a new empirical study showed that Raven scores measuring the general intelligence factor g, discovered by Wundt's student Spearman (1904), predict the magnitude of the Stroop effect in fast errors, in line with the model and evidence on alpha band activity. Also, the study provided evidence that response inhibition is absent during vocal naming in the Stroop task. To conclude, Wundt's model has stood the test of time and provides a number of enduring lessons for our understanding of attention and performance. (PsycInfo Database Record (c) 2021 APA, all rights reserved).