The relative timing of syntactic and semantic processes in sentence comprehension.

The functional primacy of syntactic over semantic processes was put to test in an auditory event-related brain potentials study using sentences in which the final words were semantically and/or syntactically incongruent with the prior context. Crucially, these words encoded the syntactically relevant word category information in the suffix, available only after the word stem which carried the semantic information. Semantic violations elicited an N400 and syntactic violations a biphasic LAN-P600 pattern. Words that were semantically and syntactically incongruent with the context evoked a biphasic LAN-P600 ERP pattern, but no N400. The similarity of the ERP pattern for the pure syntactic and the double violation condition provides strong evidence for a functional primacy of initial syntactic over lexical-semantic processes.

Dissociable brain mechanisms for inhibitory control: effects of interference content and working memory capacity.

In this study, event-related fMRI was used to examine whether the resolution of interference arising from two different information contents activates the same or different neuronal circuitries. In addition, we examined the extent to which these inhibitory control mechanisms are modulated by individual differences in working memory capacity. Two groups of participants with high and low working memory capacity [high span (HS) and low span (LS) participants, respectively] performed two versions of an item recognition task with familiar letters and abstract objects as stimulus materials. Interference costs were examined by means of the recent negative probe technique with otherwise identical testing conditions across both tasks. While the behavioral interference costs were of similar magnitude in both tasks, the underlying brain activation pattern differed between tasks: The object task interference-effects (higher activation in interference trials than in control trials) were restricted to the anterior intraparietal sulcus (IPS). Interference effects for familiar letters were obtained in the anterior IPS, the left postero-ventral and the right dorsolateral prefrontal cortex (PFC) as well as the precuneus. As the letters were more discernible than the objects, the results suggest that the critical feature for PFC and precuneus involvement in interference resolution is the saliency of stimulus-response mappings. The interference effects in the letter task were modulated by working memory capacity: LS participants showed enhanced activation for interference trials only, whereas for HS participants, who showed better performance and also lower interference costs in the letter task, the above-mentioned neuronal circuitry was activated for interference and control trials, thereby attenuating the interference effects. The latter results support the view that HS individuals allocate more attentional resources for the maintenance of task goals in the face of interfering information from preceding trials with familiar stimulus materials.

Differentiating ERAN and MMN: an ERP study.

In the present study, the early right-anterior negativity (ERAN) elicited by harmonically inappropriate chords during listening to music was compared to the frequency mismatch negativity (MMN) and the abstract-feature MMN. Results revealed that the amplitude of the ERAN, in contrast to the MMN, is specifically dependent on the degree of harmonic appropriateness. Thus, the ERAN is correlated with the cognitive processing of complex rule-based information, i.e. with the application of music-syntactic rules. Moreover, results showed that the ERAN, compared to the abstract-feature MMN, had both a longer latency, and a larger amplitude. The combined findings indicate that ERAN and MMN reflect different mechanisms of pre-attentive irregularity detection, and that, although both components have several features in common, the ERAN does not easily fit into the classical MMN framework. The present ERPs thus provide evidence for a differentiation of cognitive processes underlying the fast and pre-attentive processing of auditory information.

Working memory constraints on syntactic processing: an electrophysiological investigation.

Event-related potentials (ERPs) and reaction times (RTs) were used to study how the processing of sentences with morphosyntactic violations is constrained by working memory (WM) capacity. The available WM capacity was varied by three orthogonal manipulations: (1) syntactic complexity; (2) additional WM load; and (3) verbal WM span. The processing of the morphosyntactic violations was reflected in longer RTs in ungrammatical compared with grammatical sentences, and in an anterior negativity and a centroparietal positivity in the ERPs. While the behavioral grammaticality effect was not influenced by the WM manipulations, the ERP effects were. The amplitude of the anterior negativity was modulated by the combination of complexity and load, and by WM span. The onset of the centroparietal positivity was delayed in the high-load condition, and for the low-span group. ERPs over the course of the sentences showed a frontal negative slow wave under high WM load, largest for the low-span group. The finding that online syntactic processing is related to WM span and to additional WM load does not support the theory that there is a WM capacity specific for syntactic processing.

Musical syntax is processed in Broca's area: an MEG study.

The present experiment was designed to localize the neural substrates that process music-syntactic incongruities, using magnetoencephalography (MEG). Electrically, such processing has been proposed to be indicated by early right-anterior negativity (ERAN), which is elicited by harmonically inappropriate chords occurring within a major-minor tonal context. In the present experiment, such chords elicited an early effect, taken as the magnetic equivalent of the ERAN (termed mERAN). The source of mERAN activity was localized in Broca's area and its right-hemisphere homologue, areas involved in syntactic analysis during auditory language comprehension. We find that these areas are also responsible for an analysis of incoming harmonic sequences, indicating that these regions process syntactic information that is less language-specific than previously believed.

Syntactic gender and semantic expectancy: ERPs reveal early autonomy and late interaction.

This experiment explored the effect of semantic expectancy on the processing of grammatical gender, and vice versa, in German using event-related-potentials (ERPs). Subjects were presented with correct sentences and sentences containing an article-noun gender agreement violation. The cloze probability of the nouns was either high or low. ERPs were measured on the nouns. The low-cloze nouns evoked a larger N400 than the high-cloze nouns. Gender violations elicited a left-anterior negativity (LAN, 300-600 msec) for all nouns. An additional P600 component was found only in high-cloze nouns. The N400 was independent of the gender mismatch variable; the LAN was independent of the semantic variable, whereas an interaction of the two variables was found in the P600. This finding indicates that syntactic and semantic processes are autonomous during an early processing stage, whereas these information types interact during a later processing phase.

Brain responses during sentence reading: visual input affects central processes.

The effect of visual contrast on sentence reading was investigated using event-related brain potentials (ERPs). Under the low contrast condition semantic integration as reflected in the N400 ERP component was delayed to some degree. The left anterior negativity (LAN) reflecting initial syntactic processes, in contrast, seemed to change its characteristics as a function of visual input. In the high contrast condition the LAN preceded the P200 component whereas in the low contrast condition it was present after this component. These ERP-data from word-by-word sentence reading together with prior results from sentence listening suggest that the physical characteristics of the input must fall within a certain optimal range to guarantee ERP-effects of fast initial syntactic processes.

Concerning the automaticity of syntactic processing.

In a within-subjects design, event-related potentials were compared for two types of sentence-final syntactic errors: Incorrect verb inflection and incorrect word category (phrase structure). In a grammatical judgment task, these errors triggered robust N400 and P600 components. To assess the degree of automaticity of the underlying linguistic processes, the N400 and P600 effects were measured in a task for which the participants judged whether a word in a sentence was printed in upper case. In this physical judgment task, the N400 and P600 following verb inflection errors were greatly attenuated or absent, whereas those elicited by word category violation were only slightly diminished in amplitude. The data suggest that word category information is processed more automatically than inflectional information. The P600 appears to reflect a relatively controlled language-related process.

Priming and aging: an electrophysiological investigation of N400 and recall.

Twenty young (20.5 years) and 20 middle-aged academics (57.2 years) performed a priming-recall task which was presented in three blocks. In each block, participants read 40 word pairs after which a recall task had to be carried out. Half of the word pairs were highly associated while the others were low associated. Targets showed the N400 of the middle-aged group to be both delayed and smaller in amplitude for low-associated items. N400 of primes, however, showed no age-related latency difference but was smaller for the middle-aged group due to a positive shift. It is argued that this shift possibly indicates age differences in semantic activation or buildup of context. A reanalysis showed individual differences in word pair processing to depend on recall performance. In general, high recallers were found to show a much larger differentiation between low- and high-associated targets. This resulted from a much larger N400 component elicited by low-associated targets and a more positive ERP in the N400-region for the high-associated targets. It is suggested that the middle-aged subjects activated the expected target word to a level at least equivalent to the younger subjects, but that the activated network itself was larger/less selective particularly in subjects showing a low recall.

Human event-related brain potentials to auditory periodic noise stimuli.

Periodic noise is perceived as different from ordinary non-repeating noise due to the involvement of echoic memory. Since this stimulus does not contain simple physical cues (such as onsets or spectral shape) that might obscure sensory memory interpretations, it is a valuable tool to study sensory memory functions. We demonstrated for the first time that the processing of periodic noise can be tapped by event-related brain potentials (ERPs). Human subjects received repeating segments of noise embedded in non-repeating noise. They were instructed to detect the periodicity inherent to the stimulation. We observed a central negativity time-locked on the periodic segment that correlated to the subjects behavioral performance in periodicity detection. It is argued that the ERP result indicates an enhancement of sensory-specific processing.

When syntax meets semantics.

Three experiments concerning the processing of syntactic and semantic violations were conducted. Event-related potentials (ERPs) showed that semantic violations elicited an N400 response, whereas syntactic violations elicited two early negativities (150 and 350 ms) and a P600 response. No interaction between the semantic and early syntactic ERP effects was found. Sentence complexity and violation probability (25% vs. 75%) affected only the P600 and not the early negativities. The probability effect was taken as evidence that the P600 resembles the P3b. The temporal order of word processing in a sentence as suggested by the data was such that a more automatic syntactic analysis was performed (earlier syntactic-related negativities) in parallel with a semantic analysis (N400), after which a syntactic reanalysis was performed (P600). A reanalysis interpretation of the P600 could explain why the extent of the reanalysis differed with syntactic complexity and probability of ungrammaticality.

Focussing on aging: an electrophysiological exploration of spatial and attentional processing during reading.

Three types of selective attention tasks were presented to 24 young (20.5 years) and 24 middle-aged (57.5 years) participants. The major aim of the experiment was to explore three different aspects of selective attention, namely a pre-attentive level (i.e. auditory passive oddball task), an attentive level using spatial attention in a memory search task (i.e. selective search task) and an attentive level using a spatial cue to select a word in a reading-like situation (i.e. selective language task). The data showed that the mismatch negativity was not affected by aging although the ERPs indicated that the younger participants were paying more attention to the tones than the middle-aged. The selective search task data showed that spatial selective attention is only mildly affected by aging. The ERP-data seemed to indicate that irrelevant stimuli had a smaller impact in the middle-aged. The selective language data showed a look-a-like effect of flanker words for both age groups although the effect in the middle-aged was delayed by 30 ms and smaller. It was theorized that flankers might have smaller impact in the middle-aged. N400 was found to be smaller and delayed (90 ms) in the middle-aged participants. The overall conclusion on the basis of the three experiments is that the selectivity of processing was preserved or even enhanced in our particular group of middle-aged participants.

Language, memory, and aging: an electrophysiological exploration of the N400 during reading of memory-demanding sentences.

Twenty-four young and 24 middle-aged academics carried out a language recognition task in which sentences were presented that made either a high or a low demand on working memory (WM). The sentences ended either normally (i.e., congruent) or with an incongruous word. Middle-aged subjects had smaller WM scores, a marginally slowed down recognition performance, and a smaller and delayed N400 component. The event-related potential (ERP) difference between congruent and incongruent endings was smaller in the high-load condition for younger subjects and totally disappeared for the middle-aged subjects. ERPs for all subjects showed a WM-related positivity in the middle of the sentence and a WM-related negativity at the sentence ending. These shifts could be associated with either storage and retrieval processes or with clause wrap-up processes. Most ERP-effects were dependent on WM capacity. Age differences in sentence processing are not simply explained by age itself but depend to a large extent on individual memory capacity.

Focusing on the N400: an exploration of selective attention during reading.

In a series of two experiments, subjects read sentences wherein words were flanked in the lower visual field by irrelevant words (i.e., flankers). The visual angle between the words in the sentence and the flanker words was manipulated (i.e., 0.57 degrees, 0.97 degrees, 1.37 degrees). Sentence endings were either congruent or incongruent; incongruent endings elicited a large N400 component. Flanker effects were observed for sentence final words on electrophysiological measures during the reading task and on subsequent recognition memory performance for sentence final and new words. For both measures, the flanker effect interacted with the congruency of the sentence ending as well as the visual angle between the sentence final word and its flanker. The largest and earliest flanker effects were observed for congruent endings at the smallest visual angle (0.57 degrees); congruent endings and flankers in intermediate visual angle (0.97 degrees) conditions displayed a similar flanker-related negativity but with a longer onset latency (490 vs. 280 ms). Congruent endings and their flankers in the largest visual angle (1.57 degrees) conditions revealed no flanker effect.

Visual spatial attention to stimuli presented on the vertical and horizontal meridian: an ERP study.

In the first experiment, 48 subjects carried out a visual spatial attention task. Stimuli were presented at the vertical meridian, either above or below a fixation dot, and the subjects were instructed to attend to one of these stimulus positions and ignore the other position. In three different conditions, the distances between stimulus positions and fixation were 0.5 degrees, 0.9 degrees, and 1.3 degrees. Subjects searched for the presence of prememorized target letters at the attended location: memory load was one or four items in different conditions. The P1/N1 enhancement typically found on the horizontal dimension was not observed on the vertical dimension. Instead, a positive shift of the attended compared with the unattended stimuli was found, which was most prominent at anterior electrodes. This positivity showed effects of the distance manipulation. The N2b-P3a effects of attention and the effect of memory load (search negativity) normally present in this kind of selective search task were also found. Reaction times were faster when attention was directed above fixation than when it was directed below fixation. The event-related potential data suggested that this difference could be attributed to a more efficient neglecting of irrelevant stimuli presented below fixation. In Experiment 2, we examined whether the absence of the P1/N1 enhancement as the result of spatial attention in Experiment 1 could be attributed to (a) the presentation of stimuli along the vertical meridian instead of along the horizontal meridian, (b) the use of midline electrodes instead of lateralized electrodes, and (c) the relatively small spatial separation between the relevant and irrelevant stimuli. Twelve subjects searched for the presence of a single target letter at an attended position in three different conditions. In two of the conditions the letters were presented to the left or right of fixation. The distance between fixation and the stimulus positions was 1.3 degrees in one of these conditions and 3 degrees in the other condition. In the third condition, the stimuli were presented at 3 degrees above or below fixation. In all three conditions effects similar to those in Experiment 1 were observed. In addition, in all three conditions an enhancement of the P1 and N1 components was found at two lateral occipitotemporal electrodes.

An electrophysiological study of semantic processing in young and middle-aged academics.

This study explored age differences in the N400 component, described by Kutas and Hillyard as an index of semantic expectancy. A group of young students and a group of middle-aged academics read a number of congruent and incongruent sentences followed by a recognition task. Age differences were found in both accuracy and speed in the recognition task. The N400 elicited in the reading task was both delayed in latency and reduced in amplitude in the older group. These aging effects could not be attributed to early stimulus input processes because the N1 did not differ between the age groups. A re-averaging of the event-related potentials during reading as a function of subsequent recognition showed a small memory-related positivity for the younger group and a large memory-related positivity for the older group, suggesting a difference in the encoding strategies of the two groups. To check the generalizability of the results of this particular age group, a further task (a memory scanning task) was carried out. The results, a delayed P3b and an increased reaction time, matched those found in the literature.