The functional neuroanatomy of morphology in language production

Neural Correlates of Semantic Interference and Phonological Facilitation in Picture Naming: A Systematic Review and Coordinate-Based Meta-analysis

Semantic interference (SI) and phonological facilitation (PF) effects occur when multiple representations are co-activated simultaneously in complex naming paradigms, manipulating the context in which word production is set. Although the behavioral consequences of these psycholinguistic effects are well-known, the involved brain structures are still controversial. This paper aims to provide a systematic review and a coordinate-based meta-analysis of the available functional neuroimaging studies investigating SI and PF in picture naming paradigms. The included studies were fMRI experiments on healthy subjects, employing paradigms in which co-activations of representations were obtained by manipulating the naming context using semantically or phonologically related items. We examined the principal methodological aspects of the included studies, emphasizing the existing commonalities and discrepancies across single investigations. We then performed an exploratory coordinate-based meta-analysis of the reported activation peaks of neural response related to SI and PF. Our results consolidated previous findings regarding the involvement of the left inferior frontal gyrus and the left middle temporal gyrus in SI and brought out the role of bilateral inferior parietal regions in PF.

Unsupervised Text Segmentation Predicts Eye Fixations During Reading

Words typically form the basis of psycholinguistic and computational linguistic studies about sentence processing. However, recent evidence shows the basic units during reading, i.e., the items in the mental lexicon, are not always words, but could also be sub-word and supra-word units. To recognize these units, human readers require a cognitive mechanism to learn and detect them. In this paper, we assume eye fixations during reading reveal the locations of the cognitive units, and that the cognitive units are analogous with the text units discovered by unsupervised segmentation models. We predict eye fixations by model-segmented units on both English and Dutch text. The results show the model-segmented units predict eye fixations better than word units. This finding suggests that the predictive performance of model-segmented units indicates their plausibility as cognitive units. The Less-is-Better (LiB) model, which finds the units that minimize both long-term and working memory load, offers advantages both in terms of prediction score and efficiency among alternative models. Our results also suggest that modeling the least-effort principle for the management of long-term and working memory can lead to inferring cognitive units. Overall, the study supports the theory that the mental lexicon stores not only words but also smaller and larger units, suggests that fixation locations during reading depend on these units, and shows that unsupervised segmentation models can discover these units.

The neural basis of compound word processing revealed by varying semantic transparency and morphemic neighborhood size

This study investigated the neural basis of compound word processing by using fMRI and Chinese two-character compounds for lexical decision. Semantic transparency and morphemic neighborhood size were manipulated to augment the processing profile for measurement. The behavioral results disclosed a semantic transparency effect and its interaction with the neighborhood size, which supported existence of a mechanism for compound processing. The fMRI results located a neural substrate in the left inferior prefrontal cortex (BA 45) which reacted in an interactive manner to the two variables. While its activities were lower when their neighborhood size was larger for processing transparent compounds, its activities became higher when their neighborhood size was larger for processing opaque compounds. When scaling to a larger scope, the function of this mechanism fitted well with the theoretical account of unification function of the left inferior frontal cortex for language processing.

Psycholinguistic norms for a set of 506 French compound words

Compounds are morphologically complex words made of different linguistic parts. They are very prevalent in a number of languages such as French. Different psycholinguistic characteristics of compounds have been used in certain studies to investigate the mechanisms involved in compound processing (see Table 7). We provide psycholinguistic norms for a set of 506 French compound words. The words were normed on seven characteristics: lexeme meaning dominance, semantic transparency, sensory experience, conceptual familiarity, imageability, age of acquisition (AoA) and subjective frequency. Reliability measures were computed for the collected norms. Descriptive statistical analyses, and correlational and multiple regression analyses were performed. We also report some comparisons made between our normative data and certain norms obtained in other similar studies. The entire set of norms, which will be very useful to researchers investigating the processing of compounds, is available as Supplemental Material.

German Language Adaptation of the NAVS (NAVS-G) and of the NAT (NAT-G): Testing Grammar in Aphasia

Grammar provides the framework for understanding and producing language. In aphasia, an acquired language disorder, grammatical deficits are diversified and widespread. However, the few assessments for testing grammar in the German language do not consider current linguistic, psycholinguistic, and functional imaging data, which have been shown to be crucial for effective treatment. This study developed German language versions of the Northwestern Assessment of Verbs and Sentences (NAVS-G) and the Northwestern Anagram Test (NAT-G) to examine comprehension and production of verbs, controlling for the number and optionality of verb arguments, and sentences with increasing syntactic complexity. The NAVS-G and NAT-G were tested in 27 healthy participants, 15 right hemispheric stroke patients without aphasia, and 15 stroke patients with mild to residual aphasia. Participants without aphasia showed near-perfect performance, with the exception of (object) relative sentences, where accuracy was associated with educational level. In each patient with aphasia, deficits in more than one subtest were observed. The within and between population-groups logistic mixed regression analyses identified significant impairments in processing syntactic complexity at the verb and sentence levels. These findings indicate that the NAVS-G and NAT-G have potential for testing grammatical competence in (German) stroke patients.

Morphological facilitation and semantic interference in compound production: An ERP study

This study investigates the production of nominal compounds (Experiment 1) and simple nouns (Experiment 2) in a picture-word interference (PWI) paradigm to test models of morpho-lexical representation and processing. The continuous electroencephalogram (EEG) was registered and event-related brain potentials [ERPs] were analyzed in addition to picture-naming latencies. Experiment 1 used morphologically and semantically related distractor words to tap into different pre-articulatory planning stages during compound production. Relative to unrelated distractors, naming was speeded when distractors corresponded to morphemes of the compound (sun or flower for the target sunflower), but slowed when distractors were from the same semantic category as the compound (tulip ➔ sunflower). Distractors from the same category as the compound's first constituent (moon ➔ sunflower) had no influence. The diverging effects for semantic and morphological distractors replicate results from earlier studies. ERPs revealed different effects of morphological and semantic distractors with an interesting time course: morphological effects had an earlier onset. Comparable to the naming latencies, no ERP effects were obtained for distractors from the same semantic category as the compound's first constituent. Experiment 2 investigated the effectiveness of the latter distractors, presenting them with pictures of the compounds' first constituents (e.g., moon ➔ sun). Interference was confirmed both behaviorally and in the ERPs, showing that the absence of an effect in Experiment 1 was not due to the materials used. Considering current models of speech production, the data are best explained by a cascading flow of activation throughout semantic, lexical and morpho-phonological steps of speech planning.

Morphological and Whole-Word Semantic Processing Are Distinct: Event Related Potentials Evidence From Spoken Word Recognition in Chinese

Behavioral and imaging studies in alphabetic languages have shown that morphological processing is a discrete and independent element of lexical access. However, there is no explicit marker of morphological structure in Chinese complex words, such that the extent to which morpheme meaning is related to word meaning is unknown. Event-related potentials (ERPs) were used in the present study to investigate the dissociation of morphemic and whole-word meaning in an auditory-auditory primed lexical decision task. All the prime and target words are compounds consisting of two Chinese morphemes. The relationship between morpheme and whole-word meaning was manipulated while controlling the phonology and orthography of the first syllable in each prime-target pair. A clear dissociation was found between morphemic and whole-word meaning on N400 amplitude and topography. Specifically, sharing a morpheme produced a larger N400 in the anterior-central electrode sites, while sharing whole-word meaning produced a smaller N400 in central-posterior electrode sites. In addition, the morphological N400 effect was negatively correlated with the participants' reading ability, with better readers needing less orthographic information to distinguish different morphemes in compound words. These findings indicate that morphological and whole-word meaning are dissociated in spoken Chinese compound word recognition and that even in the spoken language modality, good readers are better able to access the meaning of individual morphemes in Chinese compound word processing.

Morphological processing in the brain: The good (inflection), the bad (derivation) and the ugly (compounding)

There is considerable behavioral evidence that morphologically complex words such as 'tax-able' and 'kiss-es' are processed and represented combinatorially. In other words, they are decomposed into their constituents 'tax' and '-able' during comprehension (reading or listening), and producing them might also involve on-the-spot combination of these constituents (especially for inflections). However, despite increasing amount of neurocognitive research, the neural mechanisms underlying these processes are still not fully understood. The purpose of this critical review is to offer a comprehensive overview on the state-of-the-art of the research on the neural mechanisms of morphological processing. In order to take into account all types of complex words, we include findings on inflected, derived, and compound words presented both visually and aurally. More specifically, we cover a wide range of electro- and magnetoencephalography (EEG and MEG, respectively) as well as structural/functional magnetic resonance imaging (s/fMRI) studies that focus on morphological processing. We present the findings with respect to the temporal course and localization of morphologically complex word processing. We summarize the observed findings, their interpretations with respect to current psycholinguistic models, and discuss methodological approaches as well as their possible limitations.

Investigating the flow of information during speaking: the impact of morpho-phonological, associative, and categorical picture distractors on picture naming

In three experiments, participants named target pictures by means of German compound words (e.g., Gartenstuhl–garden chair), each accompanied by two different distractor pictures (e.g., lawn mower and swimming pool). Targets and distractor pictures were semantically related either associatively (garden chair and lawn mower) or by a shared semantic category (garden chair and wardrobe). Within each type of semantic relation, target and distractor pictures either shared morpho-phonological (word-form) information (Gartenstuhl with Gartenzwerg, garden gnome, and Gartenschlauch, garden hose) or not. A condition with two completely unrelated pictures served as baseline. Target naming was facilitated when distractor and target pictures were morpho-phonologically related. This is clear evidence for the activation of word-form information of distractor pictures. Effects were larger for associatively than for categorically related distractors and targets, which constitute evidence for lexical competition. Mere categorical relatedness, in the absence of morpho-phonological overlap, resulted in null effects (Experiments 1 and 2), and only speeded target naming when effects reflect only conceptual, but not lexical processing (Experiment 3). Given that distractor pictures activate their word forms, the data cannot be easily reconciled with discrete serial models. The results fit well with models that allow information to cascade forward from conceptual to word-form levels.

Word tones cueing morphosyntactic structure: Neuroanatomical substrates and activation time-course assessed by EEG and fMRI

Previous studies distinguish between right hemisphere-dominant processing of prosodic/tonal information and left-hemispheric modulation of grammatical information as well as lexical tones. Swedish word accents offer a prime testing ground to better understand this division. Although similar to lexical tones, word accents are determined by words' morphosyntactic structure, which enables listeners to use the tone at the beginning of a word to predict its grammatical ending. We recorded electrophysiological and hemodynamic brain responses to words where stem tones matched or mismatched inflectional suffixes. Tones produced brain potential effects after 136 ms, correlating with subject variability in average BOLD in left primary auditory cortex, superior temporal gyrus, and inferior frontal gyrus. Invalidly cued suffixes activated the left inferior parietal lobe, arguably reflecting increased processing cost of their meaning. Thus, interaction of word accent tones with grammatical morphology yielded a rapid neural response correlating in subject variability with activations in predominantly left-hemispheric brain areas.

Distinct morphological processing of recently learned compound words: An ERP study

Our vocabulary is, at least in principle, infinite. We can create new words combining existing ones in meaningful ways to form new linguistic expressions. The present study investigated the morphological processing of novel compound words in overt speech production. Native speakers of Dutch learned a series of new compounds (e.g. appelgezicht, 'apple-face') that were later used as primes in a morphological priming task. In this protocol, primes were compound words morphologically related to a target's picture name (e.g. appelgezicht was used for a picture of an apple, Dutch appel). The novel primes were compared with corresponding familiar compounds sharing a free morpheme (e.g. appelmoes, 'applesauce') and with unrelated compounds. Participants were required to read aloud words and to name pictures in a long-lag design. Behavioral and event-related potentials (ERPs) data were collected in two sessions, separated by 48h. Clear facilitation of picture naming latencies was obtained when pictures were paired with morphological related words. Notably, our results show that novel compounds have a stronger priming effect than familiar compounds in both sessions, which is expressed in a marked reduction in target naming latencies and a decrease in the N400 amplitude. These results suggest that participants focused more on the separate constituents when reading novel primes than in the case of existing compounds.

Morphological priming during language switching: an ERP study

Bilingual language control (BLC) is a much-debated issue in recent literature. Some models assume BLC is achieved by various types of inhibition of the non-target language, whereas other models do not assume any inhibitory mechanisms. In an event-related potential (ERP) study involving a long-lag morphological priming paradigm, participants were required to name pictures and read aloud words in both their L1 (Dutch) and L2 (English). Switch blocks contained intervening L1 items between L2 primes and targets, whereas non-switch blocks contained only L2 stimuli. In non-switch blocks, target picture names that were morphologically related to the primes were named faster than unrelated control items. In switch blocks, faster response latencies were recorded for morphologically related targets as well, demonstrating the existence of morphological priming in the L2. However, only in non-switch blocks, ERP data showed a reduced N400 trend, possibly suggesting that participants made use of a post-lexical checking mechanism during the switch block.

Primary progressive aphasia and the evolving neurology of the language network

Primary progressive aphasia (PPA) is caused by selective neurodegeneration of the language-dominant cerebral hemisphere; a language deficit initially arises as the only consequential impairment and remains predominant throughout most of the course of the disease. Agrammatic, logopenic and semantic subtypes, each reflecting a characteristic pattern of language impairment and corresponding anatomical distribution of cortical atrophy, represent the most frequent presentations of PPA. Such associations between clinical features and the sites of atrophy have provided new insights into the neurology of fluency, grammar, word retrieval, and word comprehension, and have necessitated modification of concepts related to the functions of the anterior temporal lobe and Wernicke's area. The underlying neuropathology of PPA is, most commonly, frontotemporal lobar degeneration in the agrammatic and semantic forms, and Alzheimer disease (AD) pathology in the logopenic form; the AD pathology often displays atypical and asymmetrical anatomical features consistent with the aphasic phenotype. The PPA syndrome reflects complex interactions between disease-specific neuropathological features and patient-specific vulnerability. A better understanding of these interactions might help us to elucidate the biology of the language network and the principles of selective vulnerability in neurodegenerative diseases. We review these aspects of PPA, focusing on advances in our understanding of the clinical features and neuropathology of PPA and what they have taught us about the neural substrates of the language network.

"hotdog", not "hot" "dog": The phonological planning of compound words

Do we say dog when we say hotdog? In five experiments using the implicit priming paradigm, we assessed whether nominal compounds composed of two free morphemes like sawdust or fishbowl are prepared for production at the segmental level in the same way that two-syllable monomorphemic words (e.g. bandit) are, or instead as sequences of separable words (e.g. full bowl or grey dust). The experiments demonstrated that nominal compounds are planned as a single sequence, not as two sequences. Specifically, the onset of the second component of the compound (e.g. /d/ in sawdust) did not act as a primeable starting point, although comparable onsets did when that component was an independent word (grey dust). We conclude that there may be a dog in hotdog at the morpheme level, but not when phonological segments are prepared for production.

Enhancement and suppression in a lexical interference fMRI-paradigm

Previous picture-word interference (PWI) fMRI-paradigms revealed ambiguous mechanisms underlying facilitation and inhibition in healthy subjects. Lexical distractors revealed increased (enhancement) or decreased (suppression) activation in language and monitoring/control areas. Performing a secondary examination and data analysis, we aimed to illuminate the relation between behavioral and neural interference effects comparing target-related distractors (REL) with unrelated distractors (UNREL). We hypothesized that interference involves both (A) suppression due to priming and (B) enhancement due to simultaneous distractor and target processing. Comparisons to UNREL should remain distractor unspecific even at a low threshold. (C) Distractor types with common characteristics should reveal overlapping brain areas. In a 3T MRI scanner, participants were asked to name pictures while auditory words were presented (stimulus onset asynchrony [SOA] = -200 msec). Associatively and phonologically related distractors speeded responses (facilitation), while categorically related distractors slowed them down (inhibition) compared to UNREL. As a result, (A) reduced brain activations indeed resembled previously reported patterns of neural priming. Each target-related distractor yielded suppressions at least in areas associated with vision and conflict/competition monitoring (anterior cingulate cortex [ACC]), revealing least priming for inhibitors. (B) Enhancements concerned language-related but distractor-unspecific regions. (C) Some wider brain regions were commonly suppressed for combinations of distractor types. Overlapping areas associated with conceptual priming were found for facilitatory distractors (inferior frontal gyri), and areas related to phonetic/articulatory processing (precentral gyri and left parietal operculum/insula) for distractors sharing feature overlap. Each distractor with semantic relatedness revealed nonoverlapping suppressions in lexical-phonological areas (superior temporal regions). To conclude, interference combines suppression of areas well known from neural priming and enhancement of language-related areas caused by dual activation from target and distractor. Differences between interference and priming need to be taken into account. The present interference paradigm has the potential to reveal the functioning of word-processing stages, cognitive control, and responsiveness to priming at the same time.

Speaking of which: dissecting the neurocognitive network of language production in picture naming

The noninvasive methods of cognitive neuroscience offer new possibilities to study language. We used neuronavigated multisite transcranial magnetic stimulation (TMS) to determine the functional relevance of 1) the posterior part of left superior temporal gyrus (Wernicke's area), 2) a midportion of Broca's area (slightly posterior/superior to apex of vertical ascending ramus), and 3) the midsection of the left middle temporal gyrus (MTG), during overt picture naming. Our chronometric TMS design enabled us to chart the time points at which neural activity in each of these regions functionally contributes to overt speech production. Our findings demonstrate that the midsection of left MTG becomes functionally relevant at 225 ms after picture onset, followed by Broca's area at 300 ms and Wernicke's area at 400 ms. Interestingly, during this late time window, the left MTG shows a second peak of functional relevance. Each area thus contributed during the speech production process at different stages, suggesting distinct underlying functional roles within this complex multicomponential skill. These findings are discussed and framed in the context of psycholinguistic models of speech production according to which successful speaking relies on intact, spatiotemporally specific feed forward and recurrent feedback loops within a left-hemispheric fronto-temporal brain connectivity network.