Decomposition of morphologically complex words in English: evidence from event-related brain potentials

Acoustic and language-specific sources for phonemic abstraction from speech

Spoken language comprehension requires abstraction of linguistic information from speech, but the interaction between auditory and linguistic processing of speech remains poorly understood. Here, we investigate the nature of this abstraction using neural responses recorded intracranially while participants listened to conversational English speech. Capitalizing on multiple, language-specific patterns where phonological and acoustic information diverge, we demonstrate the causal efficacy of the phoneme as a unit of analysis and dissociate the unique contributions of phonemic and spectrographic information to neural responses. Quantitive higher-order response models also reveal that unique contributions of phonological information are carried in the covariance structure of the stimulus-response relationship. This suggests that linguistic abstraction is shaped by neurobiological mechanisms that involve integration across multiple spectro-temporal features and prior phonological information. These results link speech acoustics to phonology and morphosyntax, substantiating predictions about abstractness in linguistic theory and providing evidence for the acoustic features that support that abstraction.

Visual event-related potentials reveal the early whole-word lexical processing of Chinese two-character words

Morphologically complex words are common across different languages, especially in Chinese, because more than 90% of common modern Chinese words are complex words. Many behavioral studies have suggested the whole-word processing of Chinese complex words, but the neural correlates of whole-word processing remain unclear. Previous electrophysiological studies revealed automatic and early (∼250 ms) access to the orthographic forms of monomorphic words in the ventral occipitotemporal area. In this study, we investigated whether there is also automatic and early orthographic recognition of Chinese complex words (as whole units) by recording event-related potentials (ERPs). A total of 150 two-character words and 150 two-character pseudowords composed of the same 300 characters (morphemes) were pseudorandomly presented to proficient Chinese readers. Participants were required to determine the color of each stimulus in the color decision task and to determine whether each stimulus was a word in the lexical decision task. The two constituent characters of each stimulus were horizontally arranged in Experiment 1 and vertically arranged in Experiment 2. The results revealed a significant early ERP difference between words and pseudowords approximately 250-300 ms after stimulus onset in the parieto-occipital scalp region. The early ERP difference was more prominent in the color decision task than in the lexical decision task, more prominent in Experiment 1 than in Experiment 2, and more prominent in the left parieto-occipital scalp region than in the right. Source analysis results showed that the early ERP difference originated from the left ventral occipitotemporal cortex. These results reflected early and automatic access to whole-word orthographic representations of Chinese complex words in the left ventral occipitotemporal cortex.

What Language Disorders Reveal About the Mechanisms of Morphological Processing

We addressed an understudied topic in the literature of language disorders, that is, processing of derivational morphology, a domain which requires integration of semantic and syntactic knowledge. Current psycholinguistic literature suggests that word processing involves morpheme recognition, which occurs immediately upon encountering a complex word. Subsequent processes take place in order to interpret the combination of stem and affix. We investigated the abilities of individuals with agrammatic (PPA-G) and logopenic (PPA-L) variants of primary progressive aphasia (PPA) and individuals with stroke-induced agrammatic aphasia (StrAg) to process pseudowords which violate either the syntactic (word class) rules (*reheavy) or the semantic compatibility (argument structure specifications of the base form) rules (*reswim). To this end, we quantified aspects of word knowledge and explored how the distinct deficits of the populations under investigation affect their performance. Thirty brain-damaged individuals and 10 healthy controls participated in a lexical decision task. We hypothesized that the two agrammatic groups (PPA-G and StrAg) would have difficulties detecting syntactic violations, while no difficulties were expected for PPA-L. Accuracy and Reaction Time (RT) patterns indicated: the PPA-L group made fewer errors but yielded slower RTs compared to the two agrammatic groups which did not differ from one another. Accuracy rates suggest that individuals with PPA-L distinguish *reheavy from *reswim, reflecting access to and differential processing of syntactic vs. semantic violations. In contrast, the two agrammatic groups do not distinguish between *reheavy and *reswim. The lack of difference stems from a particularly impaired performance in detecting syntactic violations, as they were equally unsuccessful at detecting *reheavy and *reswim. Reduced grammatical abilities assessed through language measures are a significant predictor for this performance, suggesting that the "hardware" to process syntactic information is impaired. Therefore, they can only judge violations semantically where both *reheavy and *reswim fail to pass as semantically ill-formed. This finding further suggests that impaired grammatical knowledge can affect word level processing as well. Results are in line with the psycholinguistic literature which postulates the existence of various stages in accessing complex pseudowords, highlighting the contribution of syntactic/grammatical knowledge. Further, it points to the worth of studying impaired language performance for informing normal language processes.

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.

Brain signatures of early lexical and morphological learning of a new language

Morphology is an important part of language processing but little is known about how adult second language learners acquire morphological rules. Using a word-picture associative learning task, we have previously shown that a brief exposure to novel words with embedded morphological structure (suffix for natural gender) is enough for language learners to acquire the hidden morphological rule. Here we used this paradigm to study the brain signatures of early morphological learning in a novel language in adults. Behavioural measures indicated successful lexical (word stem) and morphological (gender suffix) learning. A day after the learning phase, event-related brain potentials registered during a recognition memory task revealed enhanced N400 and P600 components for stem and suffix violations, respectively. An additional effect observed with combined suffix and stem violations was an enhancement of an early N2 component, most probably related to conflict-detection processes. Successful morphological learning was also evident in the ERP responses to the subsequent rule-generalization task with new stems, where violation of the morphological rule was associated with an early (250-400ms) and late positivity (750-900ms). Overall, these findings tend to converge with lexical and morphosyntactic violation effects observed in L1 processing, suggesting that even after a short exposure, adult language learners can acquire both novel words and novel morphological rules.

Semantic prediction in language comprehension: evidence from brain potentials

Do people predict specific word-forms during language comprehension? In an Event-Related Potential (ERP) study participants read German sentences with predictable (The goalkeeper claims that the slick ball was easy to CATCH.) and unpredictable (The kids boasted that the young horse was easy to SADDLE.) verbs. Verbs were either consistent with the expected word-form (catch/saddle) or inconsistent and therefore led to ungrammaticality (*catches/*saddles). ERPs within the N400 time-window were modulated by predictability but not by the surface-form of the verbs, suggesting that no exact word-forms were predicted. Based on our results we will argue that predictions included semantic rather than form-information. Furthermore, ungrammatical verbs led to a strong P600, probably due to task-saliency whereas correct unpredictable verbs elicited an anterior post-N400 positivity. Because the contexts were moderately constraining, this might reflect discourse revision processes rather than inhibition of a predicted word.

Do Morphemes Matter when Reading Compound Words with Transposed Letters? Evidence from Eye-Tracking and Event-Related Potentials

The current study investigates the online processing consequences of encountering compound words with transposed letters (TLs), to determine if TLs that cross morpheme boundaries are more disruptive to reading than those within a single morpheme, as would be predicted by accounts of obligatory morpho-orthopgrahic decomposition. Two measures of online processing, eye movements and event-related potentials (ERPs), were collected in separate experiments. Participants read sentences containing correctly spelled compound words (cupcake), or compounds with TLs occurring either across morpheme boundaries (cucpake) or within one morpheme (cupacke). Results showed that between- and within-morpheme transpositions produced equal processing costs in both measures, in the form of longer reading times (Experiment 1) and a late posterior positivity (Experiment 2) that did not differ between conditions. Findings converge to suggest that within- and between-morpheme TLs are equally disruptive to recognition, providing evidence against obligatory morpho-orthographic processing and in favor of whole-word access of English compound words during sentence reading.

Effects of Grammaticality and Morphological Complexity on the P600 Event-Related Potential Component

We investigated interactions between morphological complexity and grammaticality on electrophysiological markers of grammatical processing during reading. Our goal was to determine whether morphological complexity and stimulus grammaticality have independent or additive effects on the P600 event-related potential component. Participants read sentences that were either well-formed or grammatically ill-formed, in which the critical word was either morphologically simple or complex. Results revealed no effects of complexity for well-formed stimuli, but the P600 amplitude was significantly larger for morphologically complex ungrammatical stimuli than for morphologically simple ungrammatical stimuli. These findings suggest that some previous work may have inadequately characterized factors related to reanalysis during morphosyntactic processing. Our results show that morphological complexity by itself does not elicit P600 effects. However, in ungrammatical circumstances, overt morphology provides a more robust and reliable cue to morphosyntactic relationships than null affixation.

The Past Tense Debate Revisited: Electrophysiological Evidence for Subregularities of Irregular Verb Inflection

Neuropsychological research investigating mental grammar and lexicon has largely been based on the processing of regular and irregular inflection. Past tense inflection of regular verbs is assumed to be generated by a syntactic rule (e.g., show-ed), whereas irregular verbs consist of rather unsystematic alternations (e.g., caught) represented as lexical entries. Recent morphological accounts, however, hold that irregular inflection is not entirely rule-free but relies on morphological principles. These subregularities are computed by the syntactic system. We tested this latter hypothesis by examining alternations of irregular German verbs as well as pseudowords using ERPs. Participants read series of irregular verb inflection including present tense, past participle, and past tense forms embedded in minimal syntactic contexts. The critical past tense form was correct (e.g., er sang [he sang]) or incorrect by being either partially consistent (e.g., *er sung [*he sung]) or inconsistent (e.g., *er sing [*he sing]) with the proposed morphological principles. Correspondingly, in a second experimental block, pseudowords (e.g., tang/*tung/*ting) were presented. ERPs for real words revealed a biphasic ERP pattern consisting of a negativity and P600 for both incorrect forms in comparison to the correct equivalents. Most interestingly, the P600 amplitude for the incorrect forms was gradually modulated by the type of anomaly with medium amplitude for consistent past tense forms and largest amplitude for inconsistent past tense forms. ERPs for pseudoword past tense forms showed a similar gradual modulation of N400. The findings support the assumption that irregular verbs are processed by rule-based mechanisms because of subregularities of their past tense inflection.

Changes in functional connectivity within the fronto-temporal brain network induced by regular and irregular Russian verb production

Functional connectivity between brain areas involved in the processing of complex language forms remains largely unexplored. Contributing to the debate about neural mechanisms underlying regular and irregular inflectional morphology processing in the mental lexicon, we conducted an fMRI experiment in which participants generated forms from different types of Russian verbs and nouns as well as from nonce stimuli. The data were subjected to a whole brain voxel-wise analysis of context dependent changes in functional connectivity [the so-called psychophysiological interaction (PPI) analysis]. Unlike previously reported subtractive results that reveal functional segregation between brain areas, PPI provides complementary information showing how these areas are functionally integrated in a particular task. To date, PPI evidence on inflectional morphology has been scarce and only available for inflectionally impoverished English verbs in a same-different judgment task. Using PPI here in conjunction with a production task in an inflectionally rich language, we found that functional connectivity between the left inferior frontal gyrus (LIFG) and bilateral superior temporal gyri (STG) was significantly greater for regular real verbs than for irregular ones. Furthermore, we observed a significant positive covariance between the number of mistakes in irregular real verb trials and the increase in functional connectivity between the LIFG and the right anterior cingulate cortex in these trails, as compared to regular ones. Our results therefore allow for dissociation between regularity and processing difficulty effects. These results, on the one hand, shed new light on the functional interplay within the LIFG-bilateral STG language-related network and, on the other hand, call for partial reconsideration of some of the previous findings while stressing the role of functional temporo-frontal connectivity in complex morphological processes.

Processing morphologically complex words in second-language learners: the effect of proficiency

The present study explored how the processing of morphologically complex words in second-language (L2) learners changes as their proficiency increases. ERPs were recorded from highly proficient and less proficient L2 learners, using the repetition priming paradigm. Three experimental conditions were investigated: morphological related/unrelated pairs, semantically related/unrelated pairs, and form related/unrelated pairs. The presence of priming in each condition was assessed by comparing responses to targets preceded by related primes with those preceded by unrelated primes. ERP results showed that highly proficient L2 learners demonstrated priming effect within 350-550 ms in the morphological condition, associating with an N400 reduction, while less proficient L2 learners showed no morphological priming effect within the N400 range. Besides, form priming effect was observed in both highly proficient and less proficient L2 learners within 400-450 ms and 450-500 ms, and semantic inhibiting effect was observed in both groups within 450-500 ms, suggesting that less proficient L2 learners were equally sensitive to the word form and meaning. The ERP results indicate that highly proficient L2 learners manifest rule-based decomposition, while less proficient L2 learners rely more on lexical storage in processing morphologically complex words. Less proficient L2 learners have not developed the decomposing mechanism, despite their sensitivity to word form and meaning. The way in which morphologically complex words are processed in L2 learners does change as their proficiency increases, validating the predictions of the declarative/procedural model.

An ER-fMRI study of Russian inflectional morphology

The generation of regular and irregular past tense verbs has long been a testing ground for different models of inflection in the mental lexicon. Behavioral studies examined a variety of languages, but neuroimaging studies rely almost exclusively on English and German data. In our fMRI experiment, participants inflected Russian verbs and nouns of different types and corresponding nonce stimuli. Irregular real and nonce verbs activated inferior frontal and inferior parietal regions more than regular verbs did, while no areas were more activated in the opposite comparison. We explain this activation pattern by increasing processing load: a parametric contrast revealed that these regions are also more activated for nonce stimuli compared to real stimuli. A very similar pattern is found for nouns. Unlike most previously obtained results, our findings are more readily compatible with the single-system approach to inflection, which does not postulate a categorical difference between regular and irregular forms.

Brain potentials during language production in children and adults: an ERP study of the English past tense

The current study examines the neural correlates of 8-to-12-year-old children and adults producing inflected word forms, specifically regular vs. irregular past-tense forms in English, using a silent production paradigm. ERPs were time-locked to a visual cue for silent production of either a regular or irregular past-tense form or a 3rd person singular present tense form of a given verb (e.g., walked/sang vs. walks/sings). Subsequently, another visual stimulus cued participants for an overt vocalization of their response. ERP results for the adult group revealed a negativity 300-450ms after the silent-production cue for regular compared to irregular past-tense forms. There was no difference in the present form condition. Children's brain potentials revealed developmental changes, with the older children demonstrating more adult-like ERP responses than the younger ones. We interpret the observed ERP responses as reflecting combinatorial processing involved in regular (but not irregular) past-tense formation.

Neural dynamics of inflectional and derivational processing in spoken word comprehension: laterality and automaticity

Rapid and automatic processing of grammatical complexity is argued to take place during speech comprehension, engaging a left-lateralized fronto-temporal language network. Here we address how neural activity in these regions is modulated by the grammatical properties of spoken words. We used combined magneto- and electroencephalography to delineate the spatiotemporal patterns of activity that support the recognition of morphologically complex words in English with inflectional (-s) and derivational (-er) affixes (e.g., bakes, baker). The mismatch negativity, an index of linguistic memory traces elicited in a passive listening paradigm, was used to examine the neural dynamics elicited by morphologically complex words. Results revealed an initial peak 130–180 ms after the deviation point with a major source in left superior temporal cortex. The localization of this early activation showed a sensitivity to two grammatical properties of the stimuli: (1) the presence of morphological complexity, with affixed words showing increased left-laterality compared to non-affixed words; and (2) the grammatical category, with affixed verbs showing greater left-lateralization in inferior frontal gyrus compared to affixed nouns (bakes vs. beaks). This automatic brain response was additionally sensitive to semantic coherence (the meaning of the stem vs. the meaning of the whole form) in left middle temporal cortex. These results demonstrate that the spatiotemporal pattern of neural activity in spoken word processing is modulated by the presence of morphological structure, predominantly engaging the left-hemisphere’s fronto-temporal language network, and does not require focused attention on the linguistic input.

ERPs and morphological processing: the N400 and semantic composition

Both behavioral and electrophysiological evidence suggests that fluent readers decompose morphologically complex words into their constituent parts. Previous event-related potential (ERP) research has been equivocal with regard to whether the N400 component indexes morphological decomposition or the integration of the products of decomposition, a process called semantic composition. In a visual lexical decision task with college students, we recorded ERPs to a well-controlled set of words and nonwords made up of bound morphemes (discern, predict; disject, percern) or free morphemes (cobweb, earring; cobline, bobweb) and monomorphemic control words and nonwords (garlic, minnow; gartus, buzlic). For each of the three morphological types, participants were faster to respond to words than to nonwords. Furthermore, for each of the three morphological types, the amplitude of the N400 was more negative to nonwords than to matched words, an effect indicating that the N400 is more sensitive to the lexicality of the whole stimulus than to the meaningfulness of the constituent parts of the stimulus. The N400 lexicality effect was not significantly different across the three morphological types. To our knowledge, this is the first ERP study to directly compare the processing of printed sets of words composed of bound and free morphemes and monomorphemic control stimuli in order to explore the relative sensitivity of the N400 to morphological decomposition (i.e., the status of the parts) and semantic composition (i.e., the status of the whole). Our findings are consistent with an interpretation of the N400 as an index of a process of semantic composition.

The effect of morphological complexity on verbal working memory: results from Arabic speaking children

To examine the role of morphology in verbal working memory. Forty nine children, all native speakers of Arabic from the same region and of the same dialect, performed a Listening Word Span Task, whereby they had to recall Arabic uninflected words (i.e., base words), inflected words with regular (possessive) morphology, or inflected words with irregular (broken plural) morphology. Each of these words was at the end of a sentence (henceforth, target word). The participant's task was to listen to a series of sentences and then recall the target words. Recall of inflected words was significantly poorer than uninflected words, and recall of words with regular morphology was significantly poorer than recall of words with irregular morphology. These findings, albeit preliminary, suggest a role of morphology in verbal working memory. They also suggest that, at least in Arabic, regular morphological forms are decomposed into their component elements and hence impose an extra load on the central executive and episodic buffer components of working memory. Furthermore, in concert with findings from other studies, they suggest that the effect of morphology on working memory is probably language-specific. The clinical implications of the present findings are addressed.

Electrophysiological evidence for the continuous processing of linguistic categories of regular and irregular verb inflection in German

A central question concerning word recognition is whether linguistic categories are processed in continuous or categorical ways, in particular, whether regular and irregular inflection is stored and processed by the same or by distinct systems. Here, we contribute to this issue by contrasting regular (regular stem, regular suffix) with semi-irregular (regular stem, irregular suffix) and irregular (irregular stem, irregular suffix) participle formation in a visual priming experiment on German verb inflection. We measured ERPs and RTs and manipulated the inflectional and meaning relatedness between primes and targets. Inflected verb targets (e.g., leite, "head") were preceded either by themselves, by their participle (geleitet, "headed"), by a semantically related verb in the same inflection as the target (führe, "guide") or in the participle form (geführt, "guided"), or by an unrelated verb in the same inflection (nenne, "name"). Results showed that behavioral and ERP priming effects were gradually affected by verb regularity. Regular participles produced a widely distributed frontal and parietal effect, irregular participles produced a small left parietal effect, and semi-irregular participles yielded an effect in-between these two in terms of amplitude and topography. The behavioral and ERP effects further showed that the priming because of participles differs from that because of semantic associates for all verb types. These findings argue for a single processing system that generates participle priming effects for regular, semi-irregular, and irregular verb inflection. Together, the findings provide evidence that the linguistic categories of verb inflection are processed continuously. We present a single-system model that can adequately account for such graded effects.

Past tense in the brain's time: neurophysiological evidence for dual-route processing of past-tense verbs

A controversial issue in neuro- and psycholinguistics is whether regular past-tense forms of verbs are stored lexically or generated productively by the application of abstract combinatorial schemas, for example affixation rules. The success or failure of models in accounting for this particular issue can be used to draw more general conclusions about cognition and the degree to which abstract, symbolic representations and rules are psychologically and neurobiologically real. This debate can potentially be resolved using a neurophysiological paradigm, in which alternative predictions of the brain response patterns for lexical and syntactic processing are put to the test. We used magnetoencephalography (MEG) to record neural responses to spoken monomorphemic words ('hide'), pseudowords ('smide'), regular past-tense forms ('cried') and ungrammatical (overregularised) past-tense forms ('flied') in a passive listening oddball paradigm, in which lexically and syntactically modulated stimuli are known to elicit distinct patterns of the mismatch negativity (MMN) brain response. We observed an enhanced ('lexical') MMN to monomorphemic words relative to pseudowords, but a reversed ('syntactic') MMN to ungrammatically inflected past tenses relative to grammatical forms. This dissociation between responses to monomorphemic and bimorphemic stimuli indicates that regular past tenses are processed more similarly to syntactic sequences than to lexically stored monomorphemic words, suggesting that regular past tenses are generated productively by the application of a combinatorial scheme to their separately represented stems and affixes. We suggest discrete combinatorial neuronal assemblies, which bind classes of sequentially occurring lexical elements into morphologically complex units, as the neurobiological basis of regular past tense inflection.

They played with the trade: MEG investigation of the processing of past tense verbs and their phonological twins

How regular and irregular verbs are processed remains a matter of debate. Some English-speaking patients with nonfluent aphasia are especially impaired on regular past-tense forms like played, whether the task requires production, comprehension or even the judgement that “play” and “played” sound different. Within a dual-mechanism account of inflectional morphology, these deficits reflect disruption to the rule-based process that adds (or strips) the suffix -ed to regular verb stems; but the fact that the patients are also impaired at detecting the difference between word pairs like “tray” and “trade” (the latter being a phonological but not a morphological twin to “played”) suggests an important role for phonological characteristics of the regular past tense. The present study examined MEG brain responses in healthy participants evoked by spoken regular past-tense forms and phonological twin words (plus twin pseudowords and a non-speech control) presented in a passive oddball paradigm. Deviant forms (played, trade, kwade/kwayed) relative to their standards (play, tray, kway) elicited a pronounced neuromagnetic response at approximately 130 ms after the onset of the affix; this response was maximal at sensors over temporal areas of both hemispheres but stronger on the left, especially for played and kwayed. Relative to the same standards, a different set of deviants ending in /t/―—plate, trait and kwate—―produced stronger difference responses especially over the right hemisphere. Results are discussed with regard to dual- and single-mechanism theories of past tense processing and the need to consider neurobiological evidence in attempts to understand inflectional morphology.

The temporal dynamics of inflected word recognition: a masked ERP priming study of French verbs

Morphological aspects of human language processing have been suggested by some to be reducible to the combination of orthographic and semantic effects, while others propose that morphological structure is represented separately from semantics and orthography and involves distinct neuro-cognitive processing mechanisms. Here we used event-related brain potentials (ERPs) to investigate semantic, morphological and formal (orthographic) processing conjointly in a masked priming paradigm. We directly compared morphological to both semantic and formal/orthographic priming (shared letters) on verbs. Masked priming was used to reduce strategic effects related to prime perception and to suppress semantic priming effects. The three types of priming led to distinct ERP and behavioral patterns: semantic priming was not found, while formal and morphological priming resulted in diverging ERP patterns. These results are consistent with models of lexical processing that make reference to morphological structure. We discuss how they fit in with the existing literature and how unresolved issues could be addressed in further studies.

Morphological processing as we know it: an analytical review of morphological effects in visual word identification

The last 40 years have witnessed a growing interest in the mechanisms underlying the visual identification of complex words. A large amount of experimental data has been amassed, but although a growing number of studies are proposing explicit theoretical models for their data, no comprehensive theory has gained substantial agreement among scholars in the field. We believe that this is due, at least in part, to the presence of several controversial pieces of evidence in the literature and, consequently, to the lack of a well-defined set of experimental facts that any theory should be able to explain. With this review, we aim to delineate the state of the art in the research on the visual identification of complex words. By reviewing major empirical evidences in a number of different paradigms such as lexical decision, word naming, and masked and unmasked priming, we were able to identify a series of effects that we judge as reliable or that were consistently replicated in different experiments, along with some more controversial data, which we have tried to resolve and explain. We concentrated on behavioral and electrophysiological studies on inflected, derived, and compound words, so as to span over all types of complex words. The outcome of this work is an analytical summary of well-established facts on the most relevant morphological issues, such as regularity, morpheme position coding, family size, semantic transparency, morpheme frequency, suffix allomorphy, and productivity, morphological entropy, and morpho-orthographic parsing. In discussing this set of benchmark effects, we have drawn some methodological considerations on why contrasting evidence might have emerged, and have tried to delineate a target list for the construction of a new all-inclusive model of the visual identification of morphologically complex words.

Differences in word recognition between early bilinguals and monolinguals: behavioral and ERP evidence

We investigated the behavioral and brain responses (ERPs) of bilingual word recognition to three fundamental psycholinguistic factors, frequency, morphology, and lexicality, in early bilinguals vs. monolinguals. Earlier behavioral studies have reported larger frequency effects in bilinguals' nondominant vs. dominant language and in some studies also when compared to corresponding monolinguals. In ERPs, language processing differences between bilinguals vs. monolinguals have typically been found in the N400 component. In the present study, highly proficient Finnish-Swedish bilinguals who had acquired both languages during childhood were compared to Finnish monolinguals during a visual lexical decision task and simultaneous ERP recordings. Behaviorally, we found that the response latencies were overall longer in bilinguals than monolinguals, and that the effects for all three factors, frequency, morphology, and lexicality were also larger in bilinguals even though they had acquired both languages early and were highly proficient in them. In line with this, the N400 effects induced by frequency, morphology, and lexicality were larger for bilinguals than monolinguals. Furthermore, the ERP results also suggest that while most inflected Finnish words are decomposed into stem and suffix, only monolinguals have encountered high frequency inflected word forms often enough to develop full-form representations for them. Larger behavioral and neural effects in bilinguals in these factors likely reflect lower amount of exposure to words compared to monolinguals, as the language input of bilinguals is divided between two languages.

The time-course of single-word reading: evidence from fast behavioral and brain responses

We usually feel that we understand a familiar word “immediately”. However, even basic aspects of the time-line of word recognition are still controversial. Different domains of research have still not converged on a coherent account. An integration of multiple sources of information would lead to more strongly constrained theoretical models, and help finding optimal measures when monitoring specific aspects of word recognition impairments in patient groups. In our multimodal approach – combining fast behavioral measures, ERPs and EEG/MEG source estimation – we provide converging evidence for the latencies of earliest lexical and semantic information retrieval in visual word recognition. Participants performed lexical and semantic decisions (LD, SD) in a Go/NoGo paradigm. We introduced eye-blink latencies as a dependent variable, in order to measure behavioral responses that are faster and less variable than traditional button presses. We found that the earliest behavioral responses distinguishing stimulus categories can occur around 310 ms. Ex-Gaussian analysis of behavioral responses did not reveal reliable differences between LD and SD. The earliest ERP differences between Go and NoGo conditions occurred around 160 ms for both LD and SD. Distributed source analysis of combined EEG/MEG data estimated neuronal generators for the lexicality effect around 200 ms in the left anterior middle temporal lobe. Thus, behavior and brain responses provide coherent evidence that the brain starts retrieving lexical and semantic information near-simultaneously within 200 ms of word onset. Our results support models of word recognition that assume a continuous accumulation of task-related information from the stimulus, which might be described by Bayesian principles.

Spatiotemporal Dynamics of the Processing of Spoken Inflected and Derived Words: A Combined EEG and MEG Study

The spatiotemporal dynamics of the neural processing of spoken morphologically complex words are still an open issue. In the current study, we investigated the time course and neural sources of spoken inflected and derived words using simultaneously recorded electroencephalography (EEG) and magnetoencephalography (MEG) responses. Ten participants (native speakers) listened to inflected, derived, and monomorphemic Finnish words and judged their acceptability. EEG and MEG responses were time-locked to both the stimulus onset and the critical point (suffix onset for complex words, uniqueness point for monomorphemic words). The ERP results showed that inflected words elicited a larger left-lateralized negativity than derived and monomorphemic words approximately 200 ms after the critical point. Source modeling of MEG responses showed one bilateral source in the superior temporal area ∼100 ms after the critical point, with derived words eliciting stronger source amplitudes than inflected and monomorphemic words in the right hemisphere. Source modeling also showed two sources in the temporal cortex approximately 200 ms after the critical point. There, inflected words showed a more systematic pattern in source locations and elicited temporally distinct source activity in comparison to the derived word condition. The current results provide electrophysiological evidence for at least partially distinct cortical processing of spoken inflected and derived words. In general, the results support models of morphological processing stating that during the recognition of inflected words, the constituent morphemes are accessed separately. With regard to derived words, stem and suffix morphemes might be at least initially activated along with the whole word representation.

The role of Broca's area in regular past-tense morphology: an event-related potential study

It has been suggested that damage to anterior regions of the left hemisphere results in a dissociation in the perception and lexical activation of past-tense forms. Specifically, in a lexical-decision task in which past-tense primes immediately precede present-tense targets, such patients demonstrate significant priming for irregular verbs (spoke-speak), but, unlike control participants, fail to do so for regular verbs (looked-look). Here, this behavioral dissociation was first confirmed in a group of eleven patients with damage to the pars opercularis (BA 44) and pars triangularis (BA 45) of the left inferior frontal gyrus (i.e., Broca's area). Two conditions containing word-onset orthographic-phonological overlap (bead-bee, barge-bar) demonstrated that the disrupted regular-verb priming was accompanied by, and covaried with, disrupted ortho-phonological priming, regardless of whether prime stimuli contained the regular inflectional rhyme pattern. Further, the dissociation between impaired regular-verb and preserved irregular-verb priming was shown to be continuous rather than categorical; priming for weak-irregular verbs (spent-spend) was intermediate in size between that of regular verbs and strong verbs. Such continuous dissociations grounded in ortho-phonological relationships between present- and past-tense forms are predicted by single-system, connectionist approaches to inflectional morphology and not predicted by current dual-system, rule-based models. Event-related potential data demonstrated that N400 priming effects were intact for both regular and irregular verbs, suggesting that the absence of significant regular-verb priming in the response time data did not result from a disruption of lexical access, and may have stemmed instead from post-lexical events such as covert articulation, segmentation strategies, and/or cognitive control.

Graded Effects of Regularity in Language Revealed by N400 Indices of Morphological Priming

Differential electrophysiological effects for regular and irregular linguistic forms have been used to support the theory that grammatical rules are encoded using a dedicated cognitive mechanism. The alternative hypothesis is that language systematicities are encoded probabilistically in a way that does not categorically distinguish rule-like and irregular forms. In the present study, this matter was investigated more closely by focusing specifically on whether the regular–irregular distinction in English past tenses is categorical or graded. We compared the ERP priming effects of regulars (baked–bake), vowel-change irregulars (sang–sing), and “suffixed” irregulars that display a partial regularity (suffixed irregular verbs, e.g., slept–sleep), as well as forms that are related strictly along formal or semantic dimensions. Participants performed a visual lexical decision task with either visual (Experiment 1) or auditory prime (Experiment 2). Stronger N400 priming effects were observed for regular than vowel-change irregular verbs, whereas suffixed irregulars tended to group with regular verbs. Subsequent analyses decomposed early versus late-going N400 priming, and suggested that differences among forms can be attributed to the orthographic similarity of prime and target. Effects of morphological relatedness were observed in the later-going time period, however, we failed to observe true regular–irregular dissociations in either experiment. The results indicate that morphological effects emerge from the interaction of orthographic, phonological, and semantic overlap between words.

Verbal Inflectional Morphology in L1 and L2 Spanish: A Frequency Effects Study Examining Storage versus Composition

This study examines the storage vs. composition of Spanish inflected verbal forms in L1 and L2 speakers of Spanish. L2 participants were selected to have mid-to-advanced proficiency, high classroom experience, and low immersion experience, typical of medium-to-advanced foreign language learners. Participants were shown the infinitival forms of verbs from either Class I (the default class, which takes new verbs) or Classes II and III (non-default classes), and were asked to produce either first-person singular present-tense or imperfect forms, in separate tasks. In the present tense, the L1 speakers showed inflected-form frequency effects (i.e., higher frequency forms were produced faster, which is taken as a reflection of storage) for stem-changing (irregular) verb-forms from both Class I (e.g., pensar-pienso) and Classes II and III (e.g., perder-pierdo), as well as for non-stem-changing (regular) forms in Classes II/III (e.g., vender-vendo), in which the regular transformation does not appear to constitute a default. In contrast, Class I regulars (e.g., pescar-pesco), whose non-stem-changing transformation constitutes a default (e.g., it is applied to new verbs), showed no frequency effects. L2 speakers showed frequency effects for all four conditions (Classes I and II/III, regulars and irregulars). In the imperfect tense, the L1 speakers showed frequency effects for Class II/III (-ía-suffixed) but not Class I (-aba-suffixed) forms, even though both involve non-stem-change (regular) default transformations. The L2 speakers showed frequency effects for both types of forms. The pattern of results was not explained by a wide range of potentially confounding experimental and statistical factors, and does not appear to be compatible with single-mechanism models, which argue that all linguistic forms are learned and processed in associative memory. The findings are consistent with a dual-system view in which both verb class and regularity influence the storage vs. composition of inflected forms. Specifically, the data suggest that in L1, inflected verbal forms are stored (as evidenced by frequency effects) unless they are both from Class I and undergo non-stem-changing default transformations. In contrast the findings suggest that at least these L2 participants may store all inflected verb-forms. Taken together, the results support dual-system models of L1 and L2 processing in which, at least at mid-to-advanced L2 proficiency and lower levels of immersion experience, the processing of rule-governed forms may depend not on L1 combinatorial processes, but instead on memorized representations.

An Event-Related Potential Study of Cross-modal Morphological and Phonological Priming

The current work investigated whether differences in phonological overlap between the past- and present-tense forms of regular and irregular verbs can account for the graded neurophysiological effects of verb regularity observed in past-tense priming designs. Event-related potentials were recorded from sixteen healthy participants who performed a lexical-decision task in which past-tense primes immediately preceded present-tense targets. To minimize intra-modal phonological priming effects, cross-modal presentation between auditory primes and visual targets was employed, and results were compared to a companion intra-modal auditory study (Justus, Larsen, de Mornay Davies, & Swick, 2008). For both regular and irregular verbs, faster response times and reduced N400 components were observed for present-tense forms when primed by the corresponding past-tense forms. Although behavioral facilitation was observed with a pseudopast phonological control condition, neither this condition nor an orthographic-phonological control produced significant N400 priming effects. Instead, these two types of priming were associated with a post-lexical anterior negativity (PLAN). Results are discussed with regard to dual- and single-system theories of inflectional morphology, as well as intra- and cross-modal prelexical priming.

Investigating the time course of spoken word recognition: electrophysiological evidence for the influences of phonological similarity

Behavioral and modeling evidence suggests that words compete for recognition during auditory word identification, and that phonological similarity is a driving factor in this competition. The present study used event-related potentials (ERPs) to examine the temporal dynamics of different types of phonological competition (i.e., cohort and rhyme). ERPs were recorded during a novel picture-word matching task, where a target picture was followed by an auditory word that either matched the target (CONE-cone), or mismatched in one of three ways: rhyme (CONE-bone), cohort (CONE-comb), and unrelated (CONE-fox). Rhymes and cohorts differentially modulated two distinct ERP components, the phonological mismatch negativity and the N400, revealing the influences of prelexical and lexical processing components in speech recognition. Cohort mismatches resulted in late increased negativity in the N400, reflecting disambiguation of the later point of miscue and the combined influences of top-down expectations and misleading bottom-up phonological information on processing. In contrast, we observed a reduction in the N400 for rhyme mismatches, reflecting lexical activation of rhyme competitors. Moreover, the observed rhyme effects suggest that there is an interaction between phoneme-level and lexical-level information in the recognition of spoken words. The results support the theory that both levels of information are engaged in parallel during auditory word recognition in a way that permits both bottom-up and top-down competition effects.

Neural dynamics of reading morphologically complex words

Despite considerable research interest, it is still an open issue as to how morphologically complex words such as "car+s" are represented and processed in the brain. We studied the neural correlates of the processing of inflected nouns in the morphologically rich Finnish language. Previous behavioral studies in Finnish have yielded a robust inflectional processing cost, i.e., inflected words are harder to recognize than otherwise matched morphologically simple words. Theoretically this effect could stem either from decomposition of inflected words into a stem and a suffix at input level and/or from subsequent recombination at the semantic-syntactic level to arrive at an interpretation of the word. To shed light on this issue, we used magnetoencephalography to reveal the time course and localization of neural effects of morphological structure and frequency of written words. Ten subjects silently read high- and low-frequency Finnish words in inflected and monomorphemic form. Morphological complexity was accompanied by stronger and longer-lasting activation of the left superior temporal cortex from 200 ms onwards. Earlier effects of morphology were not found, supporting the view that the well-established behavioral processing cost for inflected words stems from the semantic-syntactic level rather than from early decomposition. Since the effect of morphology was detected throughout the range of word frequencies employed, the majority of inflected Finnish words appears to be represented in decomposed form and only very high-frequency inflected words may acquire full-form representations.

Interpreting dissociations between regular and irregular past-tense morphology: evidence from event-related potentials

Neuropsychological dissociations between regular and irregular English past-tense morphology have been reported using a lexical decision task in which past-tense primes immediately precede present-tense targets. We present N400 event-related potential data from healthy participants using the same design. Both regular and irregular past-tense forms primed corresponding present-tense forms, but with a longer duration for irregular verbs. Phonological control conditions suggested that differences in formal overlap between prime and target contribute to, but do not account for, this difference, suggesting a link between irregular morphology and semantics. Further analysis dividing the irregular verbs into two categories (weak irregular and strong) revealed that priming for strong verbs was reliably stronger than that for weak irregular and regular verbs, which were statistically indistinguishable from one another. We argue that, although we observe a regular-irregular dissociation, the nature of this dissociation is more consistent with single- than with dual-system models of inflectional morphology.

Differentiating Morphology, Form, and Meaning: Neural Correlates of Morphological Complexity

The role of morphological structure in word recognition raises issues about the nature and structure of the language system. One major issue is whether morphological factors provide an independent principle for lexical organization and processing, or whether morphological effects can be reduced to the joint contribution of form and meaning. The independence of form, meaning, and morphological structure can be directly investigated using derivationally complex words, because derived words can share form but need not share meaning (e.g., archer-arch). We used an event-related functional magnetic resonance imaging paradigm to investigate priming between pairs of words that potentially shared a stem, where this link was either semantically transparent (e.g., bravely-brave) or opaque (e.g., archer-arch). These morphologically related pairs were contrasted with identity priming (e.g., mist-mist) and priming for pairs of words that shared only form (e.g., scandal-scan) or meaning (e.g., accuse-blame). Morphologically related words produced significantly reduced activation in left frontal regions, whether the pairs were semantically transparent or opaque. The effect was not found for any of the control conditions (identity, form, or meaning). Morphological effects were observed separately from processing form and meaning and we propose that they reflect segmentation of complex derived words, a process triggered by surface morphological structure of complex words.

How children process over-regularizations: evidence from event-related brain potentials

This study examines the mental processes involved in children's on-line recognition of inflected word forms using event-related potentials (ERPs). Sixty children in three age groups (20 six- to seven-year-olds, 20 eight- to nine-year-olds, 20 eleven- to twelve-year-olds) and 23 adults (tested in a previous study) listened to sentences containing correct or incorrect German noun plural forms. In the two older child groups, as well as in the adult group, over-regularized plural forms elicited brain responses that are characteristic of combinatorial (grammatical) violations. We also found that ERP components associated with language processing change from child to adult with respect to their onsets and their topography. The ERP violation effects obtained for over-regularizations suggest that children (aged eight years and above) and adults employ morphological computation for processing purposes, consistent with dual-mechanism models of inflection. The observed differences between children's and adults' ERP responses are argued to result from children's smaller lexicons and from slower and less efficient processing.

Morphology, language and the brain: the decompositional substrate for language comprehension

This paper outlines a neurocognitive approach to human language, focusing on inflectional morphology and grammatical function in English. Taking as a starting point the selective deficits for regular inflectional morphology of a group of non-fluent patients with left hemisphere damage, we argue for a core decompositional network linking left inferior frontal cortex with superior and middle temporal cortex, connected via the arcuate fasciculus. This network handles the processing of regularly inflected words (such as joined or treats), which are argued not to be stored as whole forms and which require morpho-phonological parsing in order to segment complex forms into stems and inflectional affixes. This parsing process operates early and automatically upon all potential inflected forms and is triggered by their surface phonological properties. The predictions of this model were confirmed in a further neuroimaging study, using event-related functional magnetic resonance imaging (fMRI), on unimpaired young adults. The salience of grammatical morphemes for the language system is highlighted by new research showing that similarly early and blind segmentation also operates for derivationally complex forms (such as darkness or rider). These findings are interpreted as evidence for a hidden decompositional substrate to human language processing and related to a functional architecture derived from non-human primate models.

Recognition of morphologically complex words in Finnish: evidence from event-related potentials

The temporal dynamics of processing morphologically complex words was investigated by recording event-related brain potentials (ERPs) when native Finnish-speakers performed a visual lexical decision task. Behaviorally, there is evidence that recognition of inflected nouns elicits a processing cost (i.e., longer reaction times and higher error rates) in comparison to matched monomorphemic words. We aimed to reveal whether the processing cost stems from decomposition at the early visual word form level or from re-composition at the later semantic-syntactic level. The ERPs showed no early effects for morphology, but revealed an interaction with word frequency at a late N400-type component, as well as a late positive component that was larger for inflected words. These results suggest that the processing cost stems mainly from the semantic-syntactic level. We also studied the features of the morphological decomposition route by investigating the recognition of pseudowords carrying real morphemes. The results showed no differences between inflected vs. uninflected pseudowords with a false stem, but differences in relation to those with a real stem, suggesting that a recognizable stem is needed to initiate the decomposition route.

An ERP study of regular and irregular English past tense inflection

Compositionality is a critical and universal characteristic of human language. It is found at numerous levels, including the combination of morphemes into words and of words into phrases and sentences. These compositional patterns can generally be characterized by rules. For example, the past tense of most English verbs ("regulars") is formed by adding an -ed suffix. However, many complex linguistic forms have rather idiosyncratic mappings. For example, "irregular" English verbs have past tense forms that cannot be derived from their stems in a consistent manner. Whether regular and irregular forms depend on fundamentally distinct neurocognitive processes (rule-governed combination vs. lexical memorization), or whether a single processing system is sufficient to explain the phenomena, has engendered considerable investigation and debate. We recorded event-related potentials while participants read English sentences that were either correct or had violations of regular past tense inflection, irregular past tense inflection, syntactic phrase structure, or lexical semantics. Violations of regular past tense and phrase structure, but not of irregular past tense or lexical semantics, elicited left-lateralized anterior negativities (LANs). These seem to reflect neurocognitive substrates that underlie compositional processes across linguistic domains, including morphology and syntax. Regular, irregular, and phrase structure violations all elicited later positivities that were maximal over midline parietal sites (P600s), and seem to index aspects of controlled syntactic processing of both phrase structure and morphosyntax. The results suggest distinct neurocognitive substrates for processing regular and irregular past tense forms: regulars depending on compositional processing, and irregulars stored in lexical memory.

The Role of the Striatum in Processing Language Rules: Evidence from Word Perception in Huntington's Disease

On the assumption that linguistic faculties reflect both lexical storage in the temporal cortex and combinatorial rules in the striatal circuits, several authors have shown that striatal-damaged patients are impaired with conjugation rules while retaining lexical knowledge of irregular verbs [Teichmann, M., Dupoux, E., Kouider, S., Brugières, P., Boissé, M. F., Baudic, S., Cesaro, P., Peschanski, M., & Bachoud-Lévi, A. C. (2005). The role of the striatum in rule application. The model of Huntington's disease at early stage. Brain, 128, 1155–1167; Ullman, M. T., Corkin, S., Coppola, M., Hickok, G., Growdon, J. H., Koroshetz, W. J., & Pinker, S. (1997). A neural dissociation within language: Evidence that the mental dictionary is part of declarative memory, and that grammatical rules are processed by the procedural system. Journal of Cognitive Neuroscience, 9, 266–276]. Yet, such impairment was documented only with explicit conjugation tasks in the production domain. Little is known about whether it generalizes to other language modalities such as perception and whether it refers to implicit language processing or rather to intentional rule operations through executive functions. We investigated these issues by assessing perceptive processing of conjugated verb forms in a model of striatal dysfunction, namely, in Huntington's Disease (HD) at early stages. Rule application and lexical processes were evaluated in an explicit task (acceptability judgments on verb and nonword forms) and in an implicit task (lexical decision on frequency-manipulated verb forms). HD patients were also assessed in executive functions, and striatal atrophy was evaluated with magnetic resonance imaging (bicaudate ratio). Results from both tasks showed that HD patients were selectively impaired for rule application but lexical abilities were spared. Bicaudate ratios correlated with rule scores on both tasks, whereas executive parameters only correlated with scores on the explicit task. We argue that the striatum has a core function in linguistic rule application generalizing to perceptive aspects of morphological operations and pertaining to implicit language processes. In addition, we suggest that the striatum may enclose computational circuits that underpin explicit manipulation of regularities.

Abstract grammatical processing of nouns and verbs in Broca's area: evidence from fMRI

The role of Broca's area in grammatical computation is unclear, because syntactic processing is often confounded with working memory, articulation, or semantic selection. Morphological processing potentially circumvents these problems. Using event-related functional magnetic resonance imaging (fMRI), we had 18 subjects silently inflect words or read them verbatim. Subtracting the activity pattern for reading from that for inflection, which indexes processes involved in inflection (holding constant lexical processing and articulatory planning) highlighted left Brodmann area (BA) 44/45 (Broca's area), BA 47, anterior insula, and medial supplementary motor area. Subtracting activity during zero inflection (the hawk; they walk) from that during overt inflection (the hawks; they walked), which highlights manipulation of phonological content, implicated subsets of the regions engaged by inflection as a whole. Subtracting activity during verbatim reading from activity during zero inflection (which highlights the manipulation of inflectional features) implicated distinct regions of BA 44, 47, and a premotor region (thereby tying these regions to grammatical features), but failed to implicate the insula or BA 45 (thereby tying these to articulation). These patterns were largely similar in nouns and verbs and in regular and irregular forms, suggesting these regions implement inflectional features cutting across word classes. Greater activity was observed for irregular than regular verbs in the anterior cingulate and supplementary motor area (SMA), possibly reflecting the blocking of regular or competing irregular candidates. The results confirm a role for Broca's area in abstract grammatical processing, and are interpreted in terms of a network of regions in left prefrontal cortex (PFC) that are recruited for processing abstract morphosyntactic features and overt morphophonological content.

Interplay between computational models and cognitive electrophysiology in visual word recognition

In this article, we discuss the relevance of electrophysiological data to the enterprise of analyzing and understanding the reading process. Specifically, we detail how the event-related brain potential (ERP) technique (and its magnetic counterpart) can aid in development of models of visual word recognition. Any viable and accurate account of reading must take into account the temporal and anatomical constraints imposed by the fact that reading is a human brain function. We believe that neurophysiological (especially, although not limited to electrophysiological) data can serve an essential reference in the development of biologically realistic models of reading. We assess just how well extant electrophysiological data comport with specific predictions of existing computational models and offer some suggestions for the kinds of research that can address some of the remaining open questions.

Neural correlates of morphological decomposition in a morphologically rich language: an fMRI study

By employing visual lexical decision and functional MRI, we studied the neural correlates of morphological decomposition in a highly inflected language (Finnish) where most inflected noun forms elicit a consistent processing cost during word recognition. This behavioral effect could reflect suffix stripping at the visual word form level and/or subsequent meaning integration at the semantic-syntactic level. The first alternative predicts increased activation for inflected vs. monomorphemic words in the left occipitotemporal cortex while the second alternative predicts left inferior frontal gyrus and/or left posterior temporal activation increases. The results show significant activation effects in the latter areas. This provides support for the second alternative, i.e., that the morphological processing cost stems from the semantic-syntactic level.