Publications

Abstract

Language comprehension involves two basic operations: the retrieval of lexical information (such as phonologic, syntactic, and semantic information) from long-term memory, and the unification of this information into a coherent representation of the overall utterance. Neuroimaging studies using hemo¬dynamic measures such as PET and fMRI have provided detailed information on which areas of the brain are involved in these language-related memory and unification operations. However, much less is known about the dynamics of the brain's language network. This chapter presents a literature review of the oscillatory neuronal dynamics of EEG and MEG data that can be observed during language comprehen¬sion tasks. From a detailed review of this (rapidly growing) literature the following picture emerges: memory retrieval operations are mostly accompanied by increased neuronal synchronization in the theta frequency range (4-7 Hz). Unification operations, in contrast, induce high-frequency neuronal synchro¬nization in the beta (12-30 Hz) and gamma (above 30 Hz) frequency bands. A desynchronization in the (upper) alpha frequency band is found for those studies that use secondary tasks, and seems to correspond with attentional processes, and with the behavioral consequences of the language comprehension process. We conclude that it is possible to capture the dynamics of the brain's language network by a careful analysis of the event-related changes in power and coherence of EEG and MEG data in a wide range of frequencies, in combination with subtle experimental manipulations in a range of language comprehension tasks. It appears then that neuronal synchrony is a mechanism by which the brain integrates the different types of information about language (such as phonological, orthographic, semantic, and syntactic infor¬mation) represented in different brain areas.

Abstract

The human brain supports acquisition mechanisms that extract structural regularities implicitly from experience without the induction of an explicit model. It has been argued that the capacity to generalize to new input is based on the acquisition of abstract representations, which reflect underlying structural regularities in the input ensemble. In this study, we explored the outcome of this acquisition mechanism, and to this end, we investigated the neural correlates of artificial syntactic classification using event-related functional magnetic resonance imaging. The participants engaged once a day during an 8-day period in a short-term memory acquisition task in which consonant-strings generated from an artificial grammar were presented in a sequential fashion without performance feedback. They performed reliably above chance on the grammaticality classification tasks on days 1 and 8 which correlated with a corticostriatal processing network, including frontal, cingulate, inferior parietal, and middle occipital/occipitotemporal regions as well as the caudate nucleus. Part of the left inferior frontal region (BA 45) was specifically related to syntactic violations and showed no sensitivity to local substring familiarity. In addition, the head of the caudate nucleus correlated positively with syntactic correctness on day 8 but not day 1, suggesting that this region contributes to an increase in cognitive processing fluency.

Abstract

We explore the nature of the oscillatory dynamics in the EEG of subjects reading sentences that contain a semantic violation. More specifically, we examine whether increases in theta (≈3–7 Hz) and gamma (around 40 Hz) band power occur in response to sentences that were either semantically correct or contained a semantically incongruent word (semantic violation). ERP results indicated a classical N400 effect. A wavelet-based time-frequency analysis revealed a theta band power increase during an interval of 300–800 ms after critical word onset, at temporal electrodes bilaterally for both sentence conditions, and over midfrontal areas for the semantic violations only. In the gamma frequency band, a predominantly frontal power increase was observed during the processing of correct sentences. This effect was absent following semantic violations. These results provide a characterization of the oscillatory brain dynamics, and notably of both theta and gamma oscillations, that occur during language comprehension.

Abstract

When faced with the noun phrase (NP) versus sentence (S) coordination ambiguity as in, for example, The thief shot the jeweller and the cop hellip, readers prefer the reading with NP-coordination (e.g., "The thief shot the jeweller and the cop yesterday") over one with two conjoined sentences (e.g., "The thief shot the jeweller and the cop panicked"). A corpus study is presented showing that NP-coordinations are produced far more often than S-coordinations, which in frequency-based accounts of parsing might be taken to explain the NP-coordination preference. In addition, we describe an eye-tracking experiment investigating S-coordinated sentences such as Jasper sanded the board and the carpenter laughed, where the poor thematic fit between carpenter and sanded argues against NP-coordination. Our results indicate that information regarding poor thematic fit was used rapidly, but not without leaving some residual processing difficulty. This is compatible with claims that thematic information can reduce but not completely eliminate garden-path effects.

Abstract

This study investigates functional interpretations of left
anterior negativities (LANs), a language-related electroencephalogram effect that has been found for syntactic and morphological violations. We focus on three possible interpretations of LANs caused by the replacement of irregular affixes with regular affixes: misapplication of morphological rules, mismatch of the presented form with analogy-based expectations, and mismatch of the presented form with stored representations. Event-related brain potentials were recorded during the visual presentation of existing and novel Dutch compounds. Existing compounds contained correct or replaced interfixes (dame + s + salons > damessalons vs. *dame + n + salons > *damensalons ‘‘women’s hairdresser salons’’), whereas novel Dutch compounds contained interfixes that were either supported or not supported by analogy to similar existing compounds
(kruidenkelken vs. ?kruidskelken ‘‘herb chalices’’); earlier studies had shown that interfixes are selected by analogy instead of rules. All compounds were presented with correct or incorrect regular plural suffixes (damessalons vs. *damessalonnen). Replacing suffixes or interfixes in existing compounds both led to increased (L)ANs between 400 and 700 msec without any evidence for different scalp distributions for interfixes and suffixes. There was no evidence for a negativity when manipulating the analogical support for interfixes in novel compounds. Together with earlier studies, these results suggest that LANs had been caused by the mismatch of the presented forms with stored forms. We discuss these findings with respect to the single/dual-route debate of morphology and LANs found for the misapplication of syntactic rules.

Abstract

The recognition of a word makes available its semantic and
syntactic properties. Using electrophysiological recordings, we
investigated whether one set of these properties is available
earlier than the other set. Dutch participants saw nouns on a
computer screen and performed push-button responses: In
one task, grammatical gender determined response hand
(left/right) and semantic category determined response execution
(go/no-go). In the other task, response hand depended
on semantic category, whereas response execution depended
on gender. During the latter task, response preparation occurred
on no-go trials, as measured by the lateralized
readiness potential: Semantic information was used for
response preparation before gender information inhibited
this process. Furthermore, an inhibition-related N2 effect
occurred earlier for inhibition by semantics than for inhibition
by gender. In summary, electrophysiological measures
of both response preparation and inhibition indicated that
the semantic word property was available earlier than the
syntactic word property when participants read single
words.

Abstract

An event-related brain potential experiment was carried out to investigate the temporal relationship
between lexical selection and the semantic integration in auditory sentence processing. Participants were
presented with spoken sentences that ended with a word that was either semantically congruent or
anomalous. Information about the moment in which a sentence-final word could uniquely be identified,
its isolation point (IP), was compared with the onset of the elicited N400 congruity effect, reflecting
semantic integration processing. The results revealed that the onset of the N400 effect occurred prior to
the IP of the sentence-final words. Moreover, the factor early or late IP did not affect the onset of the
N400. These findings indicate that lexical selection and semantic integration are cascading processes, in
that semantic integration processing can start before the acoustic information allows the selection of a
unique candidate and seems to be attempted in parallel for multiple candidates that are still compatible
with the bottom–up acoustic input.

Abstract

This study tests the recent claim that Broca’s aphasics are impaired in automatic lexical access, including the retrieval of word meaning. Subjects are required to perform a lexical decision on visually presented prime target pairs. Half of the word targets are preceded by a related word, half by an unrelated word. Primes and targets are presented with a long stimulus-onset-asynchrony (SOA) of 1400 msec and with a short SOA of 300 msec. Normal priming effects are observed in Broca’s aphasics for both SOAs. This result is discussed in the context of the claim that Broca’s aphasics suffer from an impairment in the automatic access of lexical–semantic information. It is argued that none of the current priming studies provides evidence supporting this claim, since with short SOAs priming effects have been reliably obtained in Broca’s aphasics. The results are more compatible with the claim that in many Broca’s aphasics the functional locus of their comprehension deficit is at the level of postlexical integration processes.

Abstract

Stimulus-related changes in cerebral blood oxygenation were measured using high-resolution functional magnetic resonance imaging sequentially covering visual occipital areas in contiguous sections. During dynamic imaging, healthy subjects silently viewed pseudowords, single false fonts, or length-matched strings of the same false fonts. The paradigm consisted of a sixfold alternation of an activation and a control task. With pseudowords as activation vs single false fonts as control, responses were seen mainly in medial occipital cortex. These responses disappeared when pseudowords were alternated with false font strings as the control and reappeared when false font strings instead of pseudowords served as activation and were alternated with single false fonts. The string-length contrast alone, therefore, is sufficient to account for the activation pattern observed in medial visual cortex when word-like stimuli are contrasted with single characters.

Abstract

In this study the N400 component of the event-related potential was used to investigate spoken sentence understanding in Broca's and Wernicke's aphasics. The aim of the study was to determine whether spoken sentence comprehension problems in these patients might result from a deficit in the on-line integration of lexical information. Subjects listened to sentences spoken at a normal rate. In half of these sentences, the meaning of the final word of the sentence matched the semantic specifications of the preceding sentence context. In the other half of the sentences, the sentence-final word was anomalous with respect to the preceding sentence context. The N400 was measured to the sentence-final words in both conditions. The results for the aphasic patients (n = 14) were analyzed according to the severity of their comprehension deficit and compared to a group of 12 neurologically unimpaired age-matched controls, as well as a group of 6 nonaphasic patients with a lesion in the right hemisphere. The nonaphasic brain damaged patients and the aphasic patients with a light comprehension deficit (high comprehenders, n = 7) showed an N400 effect that was comparable to that of the neurologically unimpaired subjects. In the aphasic patients with a moderate to severe comprehension deficit (low comprehenders, n = 7), a reduction and delay of the N400 effect was obtained. In addition, the P300 component was measured in a classical oddball paradigm, in which subjects were asked to count infrequent low tones in a random series of high and low tones. No correlation was found between the occurrence of N400 and P300 effects, indicating that changes in the N400 results were related to the patients' language deficit. Overall, the pattern of results was compatible with the idea that aphasic patients with moderate to severe comprehension problems are impaired in the integration of lexical information into a higher order representation of the preceding sentence context.

Abstract

The temporal properties of semantic and phonological processes in speech production were investigated in a new experimental paradigm using movement-related brain potentials. The main experimental task was picture naming. In addition, a 2-choice reaction go/no-go procedure was included, involving a semantic and a phonological categorization of the picture name. Lateralized readiness potentials (LRPs) were derived to test whether semantic and phonological information activated motor processes at separate moments in time. An LRP was only observed on no-go trials when the semantic (not the phonological) decision determined the response hand. Varying the position of the critical phoneme in the picture name did not affect the onset of the LRP but rather influenced when the LRP began to differ on go and no-go trials and allowed the duration of phonological encoding of a word to be estimated. These results provide electrophysiological evidence for early semantic activation and later phonological encoding.

Abstract

The N400 is an endogenous event-related brain potential (ERP) that is sensitive to semantic processes during language comprehension. The general question we address in this paper is which aspects of the comprehension process are manifest in the N400. The focus is on the sensitivity of the N400 to the automatic process of lexical access, or to the controlled process of lexical integration. The former process is the reflex-like and effortless behavior of computing a form representation of the linguistic signal, and of mapping this representation onto corresponding entries in the mental lexicon. The latter process concerns the integration of a spoken or written word into a higher-order meaning representation of the context within which it occurs. ERPs and reaction times (RTs) were acquired to target words preceded by semantically related and unrelated prime words. The semantic relationship between a prime and its target has been shown to modulate the amplitude of the N400 to the target. This modulation can arise from lexical access processes, reflecting the automatic spread of activation between words related in meaning in the mental lexicon. Alternatively, the N400 effect can arise from lexical integration processes, reflecting the relative ease of meaning integration between the prime and the target. To assess the impact of automatic lexical access processes on the N400, we compared the effect of masked and unmasked presentations of a prime on the N400 to a following target. Masking prevents perceptual identification, and as such it is claimed to rule out effects from controlled processes. It therefore enables a stringent test of the possible impact of automatic lexical access processes on the N400. The RT study showed a significant semantic priming effect under both unmasked and masked presentations of the prime. The result for masked priming reflects the effect of automatic spreading of activation during the lexical access process. The ERP study showed a significant N400 effect for the unmasked presentation condition, but no such effect for the masked presentation condition. This indicates that the N400 is not a manifestation of lexical access processes, but reflects aspects of semantic integration processes.

Abstract

Broca′s and Wernicke′s aphasics performed speeded lexical decisions on the third member of auditorily presented triplets consisting of two word primes followed by either a word or a nonword. In three of the four priming conditions, the second prime was a homonym with two unrelated meanings. The relation of the first prime and the target with the two meanings of the homonym was manipulated in the different priming conditions. The two readings of the ambiguous words either shared their grammatical form class (noun-noun ambiguities) or not (noun-verb ambiguities). The silent intervals between the members of the triplets were varied between 100, 500, and 1250 msec. Priming at the shortest interval is mainly attributed to automatic lexical processing, and priming at the longest interval is mainly due to forms of controlled lexical processing. For both Broca′s and Wernicke′s aphasics overall priming effects were obtained at ISIs of 100 and 500 msec, but not at an ISI of 1250 msec. This pattern of results is consistent with the view that both types of aphasics can automatically access the semantic lexicon, but might be impaired in integrating lexical-semantic information into the context. Broca′s aphasics showed a specific impairment in selecting the contextually appropriate reading of noun-verb ambiguities, which is suggested to result from a failure either in the on-line morphological parsing of complex word forms into a stem and an inflection or in the on-line exploitation of the syntactic implications of the inflectional suffix. In a final experiment patients were asked to explicitly judge the semantic relations between a subset of the primes that were used in the lexical decision study. Wernicke′s aphasics performed worse than both Broca′s aphasics and normal controls, indicating a specific impairment for these patients in consciously operating on automatically accessed lexical-semantic information.

Abstract

This paper presents event-related brain potential (ERP) data from an experiment on syntactic processing. Subjects read individual sentences containing one of three different kinds of violations of the syntactic constraints of Dutch. The ERP results provide evidence for M electrophysiological response to syntactic processing that is qualitatively different from established ERP responses to semantic processing. We refer to this electro-physiological manifestation of parsing as the Syntactic Positive Shift (SPS). The SPS was observed in an experiment in which no task demands, other than to read the input, were imposed on the subjects. The pattern of responses to the different kinds of syntactic violations suggests that the SPS indicates the impossibility for the parser to assign the preferred structure to an incoming string of words, irrespective of the specific syntactic nature of this preferred structure. The implications of these findings for further research on parsing are discussed.