Statistical learning and prosodic bootstrapping differentially affect neural synchronization during speech segmentation.

Neural oscillations constitute an intrinsic property of functional brain organization that facilitates the tracking of linguistic units at multiple time scales through brain-to-stimulus alignment. This ubiquitous neural principle has been shown to facilitate speech segmentation and word learning based on statistical regularities. However, there is no common agreement yet on whether speech segmentation is mediated by a transition of neural synchronization from syllable to word rate, or whether the two time scales are concurrently tracked. Furthermore, it is currently unknown whether syllable transition probability contributes to speech segmentation when lexical stress cues can be directly used to extract word forms. Using Inter-Trial Coherence (ITC) analyses in combinations with Event-Related Potentials (ERPs), we showed that speech segmentation based on both statistical regularities and lexical stress cues was accompanied by concurrent neural synchronization to syllables and words. In particular, ITC at the word rate was generally higher in structured compared to random sequences, and this effect was particularly pronounced in the flat condition. Furthermore, ITC at the syllable rate dynamically increased across the blocks of the flat condition, whereas a similar modulation was not observed in the stressed condition. Notably, in the flat condition ITC at both time scales correlated with each other, and changes in neural synchronization were accompanied by a rapid reconfiguration of the P200 and N400 components with a close relationship between ITC and ERPs. These results highlight distinct computational principles governing neural synchronization to pertinent linguistic units while segmenting speech under different listening conditions.

Food is special by itself: Neither valence, arousal, food appeal, nor caloric content modulate the attentional bias induced by food images.

When food cues appear in a visual context, such information is likely to influence eating behavior by enhancing attention for food cues. We investigated whether active but task-irrelevant information could modulate the attentional bias for food stimuli using a novel paradigm in which participants were purposely deceived by being enrolled in a memory experiment. A set of images were first held in working memory and then used as task-irrelevant distractors in a subsequent single target rapid serial visual presentation (RSVP) task, allowing us to investigate the attentional blink (AB) effect elicited by those images. In Experiment 1, the results revealed that food images elicited a larger AB effect than nonfood images. In three follow-up experiments, we investigated whether valence or arousal (Experiment 2), food preparation (Experiment 3), or food caloric content (Experiment 4) were factors related to the attentional bias for food. Overall, our results demonstrated that when held in working memory, food images can easily capture attention, even in circumstances in which the information retained in memory is irrelevant to solve the task, as indicated by the strong correlation found between items that were recognized in the RSVP task and the AB effect. Nonetheless, none of the food-related properties we examined were found to be associated with this attentional bias for food.

The right inferior frontal cortex in response inhibition: A tDCS-ERP co-registration study.

In any given common situation, when an individual controls him/herself or obeys and stops a current action when asked to do, it is because the brain executes an inhibitory process. This ability is essential for adaptive behaviour, and it is also a requirement for accurate performance in daily life. It has been suggested that there are two main inhibitory functions related to behaviour, as inhibition is observed to affect behaviour at different time intervals. Proactive inhibition permits the subject to control his behavioural response over time by creating a response tendency, while reactive inhibition is considered to be a process that usually inhibits an already initiated response. In this context, it has been established that inhibitory function is implemented by specific fronto-basal-ganglia circuits. In the present study, we investigated the role of the right inferior frontal cortex (rIFC) in response inhibition by combining into a single task the Go-NoGo task and the Stop-Signal task. Concurrently, we applied transcranial direct current stimulation (tDCS) over the IFC and recorded electroencephalography (EEG). Thus, we obtained online EEG measurements of the tDCS-induced modifications in the IFC together with the participant's performance in a response inhibition task. We found that applying bilateral tDCS on the IFC (right anodal/left cathodal) significantly increased proactive inhibition, although the behavioural parameters indicative of reactive inhibition were unaffected by the stimulation. Finally, the inhibitory-P3 component reflected a similar modulation under both inhibitory conditions induced by the stimulation. Our data indicates that an online tDCS-ERP approach is achievable, but that a tDCS bilateral montage may not be the most efficient one for modulating the rIFC.

Brain oscillatory activity associated with task switching and feedback processing.

In this study, we sought to dissociate event-related potentials (ERPs) and the oscillatory activity associated with signals indicating feedback about performance (outcome-based behavioral adjustment) and the signals indicating the need to change or maintain a task set (rule-based behavioral adjustment). With this purpose in mind, we noninvasively recorded electroencephalographic signals, using a modified version of the Wisconsin card sorting task, in which feedback processing and task switching could be studied separately. A similar late positive component was observed for the switch and correct feedback signals on the first trials of a series, but feedback-related negativity was observed only for incorrect feedback. Moreover, whereas theta power showed a significant increase after a switch cue and after the first positive feedback of a new series, a selective frontal beta-gamma increase was observed exclusively in the first positive feedback (i.e., after the selection of the new rule). Importantly, for the switch cue, beta-alpha activity was suppressed rather than increased. This clear dissociation between the cue and feedback stimuli in task switching emphasizes the need to accurately study brain oscillatory activity to disentangle the role of different cognitive control processes.

Language learning under working memory constraints correlates with microstructural differences in the ventral language pathway.

The present study combined behavioral measures and diffusion tensor imaging to investigate the neuroanatomical basis of language learning in relation to phonological working memory (WM). Participants were exposed to simplified artificial languages under WM constraints. The results underscore the role of the rehearsal subcomponent of WM in successful speech segmentation and rule learning. Moreover, when rehearsal was blocked task performance was correlated to the white matter microstructure of the left ventral pathway connecting frontal and temporal language-related cortical areas through the extreme/external capsule. This ventral pathway may therefore play an important additional role in language learning when the main dorsal pathway-dependent rehearsal mechanisms are not available.

Early response competition over the motor cortex underlies proactive control of error correction.

Response inhibition is a fundamental brain function that must be flexible enough to incorporate proactive goal-directed demands, along with reactive, automatic and well consolidated behaviors. However, whether proactive inhibitory processes can be explained by response competition, rather than by active top-down inhibitory control, remains still unclear. Using a modified version of the Eriksen flanker task, we examined the behavioral and electrophysiological correlates elicited by manipulating the degree of inhibitory control in a task that involved the fast amendment of errors. We observed that restraining or encouraging the correction of errors did not affect the behavioral and neural correlates associated to reactive inhibition. We rather found that an early, sustained and bilateral activation, of both the correct and the incorrect response, was required for an effective proactive inhibitory control. Selective unilateral patterns of response preparation were instead associated with defective response suppression. Our results provide behavioral and electrophysiological evidence of a simultaneous dual pre-activation of two motor commands, likely underlying a global operating mechanism suggesting competition or lateral inhibition to govern the amendment of errors. These findings are consistent with the response inhibitory processes already observed in speed-accuracy tradeoff studies, and hint at a decisive role of early response competition to determine the success of multiple-choice action selection.

The role of the anterior insular cortex in self-monitoring: A novel study protocol with electrical stimulation mapping and functional magnetic resonance imaging.

Becoming aware of one's own states is a fundamental aspect for self-monitoring, allowing us to adjust our beliefs of the world to the changing context. Previous evidence points out to the key role of the anterior insular cortex (aIC) in evaluating the consequences of our own actions, especially whenever an error has occurred. In the present study, we propose a new multimodal protocol combining electrical stimulation mapping (ESM) and functional magnetic resonance imaging (fMRI) to explore the functional role of the aIC for self-monitoring in patients undergoing awake brain surgery. Our results using a modified version of the Stroop task tackling metacognitive abilities revealed new direct evidence of the involvement of the aIC in monitoring our performance, showing increased difficulties in detecting action-outcome mismatches when stimulating a cortical site located at the most posterior part of the aIC as well as significant BOLD activations at this region during outcome incongruences for self-made actions. Based on these preliminary results, we highlight the importance of assessing the aIC's functioning during tumor resection involving this region to evaluate metacognitive awareness of the self in patients undergoing awake brain surgery. In a similar vein, a better understanding of the aIC's role during self-monitoring may help shed light on action/outcome processing abnormalities reported in several neuropsychiatric disorders such as schizophrenia, anosognosia for hemiplegia or major depression.

The effects of COMT (Val108/158Met) and DRD4 (SNP -521) dopamine genotypes on brain activations related to valence and magnitude of rewards.

People's sensitivity to reinforcing stimuli such as monetary gains and losses shows a wide interindividual variation that might in part be determined by genetic differences. Because of the established role of the dopaminergic system in the neural encoding of rewards and negative events, we investigated young healthy volunteers being homozygous for either the Valine or Methionine variant of the catechol-O-methyltransferase (COMT) codon 158 polymorphism as well as homozygous for the C or T variant of the SNP -521 polymorphism of the dopamine D4 receptor. Participants took part in a gambling paradigm featuring unexpectedly high monetary gains and losses in addition to standard gains/losses of expected magnitude while undergoing functional magnetic resonance imaging at 3 T. Valence-related brain activations were seen in the ventral striatum, the anterior cingulate cortex, and the inferior parietal cortex. These activations were modulated by the COMT polymorphism with greater effects for valine/valine participants but not by the D4 receptor polymorphism. By contrast, magnitude-related effects in the anterior insula and the cingulate cortex were modulated by the D4 receptor polymorphism with larger responses for the CC variant. These findings emphasize the differential contribution of genetic variants in the dopaminergic system to various aspects of reward processing.

Individual differences in true and false memory retrieval are related to white matter brain microstructure.

We sometimes vividly remember things that did not happen, a phenomenon with general relevance, not only in the courtroom. It is unclear to what extent individual differences in false memories are driven by anatomical differences in memory-relevant brain regions. Here we show in humans that microstructural properties of different white matter tracts as quantified using diffusion tensor imaging are strongly correlated with true and false memory retrieval. To investigate these hypotheses, we tested a large group of participants in a version of the Deese-Roediger-McDermott paradigm (recall and recognition) and subsequently obtained diffusion tensor images. A voxel-based whole-brain level linear regression analysis was performed to relate fractional anisotropy to indices of true and false memory recall and recognition. True memory was correlated to diffusion anisotropy in the inferior longitudinal fascicle, the major connective pathway of the medial temporal lobe, whereas a greater proneness to retrieve false items was related to the superior longitudinal fascicle connecting frontoparietal structures. Our results show that individual differences in white matter microstructure underlie true and false memory performance.

Neurophysiological markers of novelty processing are modulated by COMT and DRD4 genotypes.

Humans are faced with the dilemma to maintain a stable cognitive set on the one hand and to be able to redirect and switch attention to novel stimuli of potential importance. The dopaminergic system has been implicated in the balance between these two antagonistic constraints and in particular in novelty processing. Here we studied the impact of two polymorphisms affecting dopaminergic functioning (COMT Val108/158Met and DRD4 SNP -521) on neurophysiological correlates of novelty processing. Recording event-related potentials (ERPs) and oscillatory activity in a modified oddball task that featured infrequent but task-irrelevant novel sounds in addition to frequent standard and rare target tones, we examined participants homozygous for the Met or Val variant of COMT as well as homozygous for the C or T variant of DRD4. We found effects mainly on the P3a component to novel stimuli. A greater P3a amplitude was found for the COMT-ValVal group relative to MetMet. There was a tendency for DRD4-TT participants to show greater P3a amplitude and shorter P3a latency. Finally, DRD4-TT and COMT-ValVal participants showed the greatest increase of theta-power to novel stimuli. By contrast, the P3b component to target stimuli showed little influence of the studied polymorphism. Individual differences in dopaminergic genes explain part of the interindividual variance in the neural correlates of novelty but not target processing.

Time course and functional neuroanatomy of speech segmentation in adults.

The present investigation was devoted to unraveling the time-course and brain regions involved in speech segmentation, which is one of the first processes necessary for learning a new language in adults and infants. A specific brain electrical pattern resembling the N400 language component was identified as an indicator of speech segmentation of candidate words. This N400 trace was clearly elicited after a short exposure to the words of the new language and showed a decrease in amplitude with longer exposure. Two brain regions were observed to be active during this process: the posterior superior temporal gyrus and the superior part of the ventral premotor cortex. We interpret these findings as evidence for the existence of an auditory-motor interface that is responsible for isolating possible candidate words when learning a new language in adults.

ADHD candidate gene (DRD4 exon III) affects inhibitory control in a healthy sample.

BACKGROUND: Dopamine is believed to be a key neurotransmitter in the development of attention-deficit/hyperactivity disorder (ADHD). Several recent studies point to an association of the dopamine D4 receptor (DRD4) gene and this condition. More specifically, the 7 repeat variant of a variable number of tandem repeats (VNTR) polymorphism in exon III of this gene is suggested to bear a higher risk for ADHD. In the present study, we investigated the role of this polymorphism in the modulation of neurophysiological correlates of response inhibition (Go/Nogo task) in a healthy, high-functioning sample. RESULTS: Homozygous 7 repeat carriers showed a tendency for more accurate behavior in the Go/Nogo task compared to homozygous 4 repeat carriers. Moreover, 7 repeat carriers presented an increased nogo-related theta band response together with a reduced go-related beta decrease. CONCLUSIONS: These data point to improved cognitive functions and prefrontal control in the 7 repeat carriers, probably due to the D4 receptor's modulatory role in prefrontal areas. The results are discussed with respect to previous behavioral data on this polymorphism and animal studies on the impact of the D4 receptor on cognitive functions.

The impact of catechol-O-methyltransferase and dopamine D4 receptor genotypes on neurophysiological markers of performance monitoring.

Dynamic adaptations of one's behavior by means of performance monitoring are a central function of the human executive system, that underlies considerable interindividual variation. Converging evidence from electrophysiological and neuroimaging studies in both animals and humans hints at the importance of the dopaminergic system for the regulation of performance monitoring. Here, we studied the impact of two polymorphisms affecting dopaminergic functioning in the prefrontal cortex [catechol-O-methyltransferase (COMT) Val108/158Met and dopamine D4 receptor (DRD4) single-nucleotide polymorphism (SNP)-521] on neurophysiological correlates of performance monitoring. We applied a modified version of a standard flanker task with an embedded stop-signal task to tap into the different functions involved, particularly error monitoring, conflict detection and inhibitory processes. Participants homozygous for the DRD4 T allele produced an increased error-related negativity after both choice errors and failed inhibitions compared with C-homozygotes. This was associated with pronounced compensatory behavior reflected in higher post-error slowing. No group differences were seen in the incompatibility N2, suggesting distinct effects of the DRD4 polymorphism on error monitoring processes. Additionally, participants homozygous for the COMT Val allele, with a thereby diminished prefrontal dopaminergic level, revealed increased prefrontal processing related to inhibitory functions, reflected in the enhanced stop-signal-related components N2 and P3a. The results extend previous findings from mainly behavioral and neuroimaging data on the relationship between dopaminergic genes and executive functions and present possible underlying mechanisms for the previously suggested association between these dopaminergic polymorphisms and psychiatric disorders as schizophrenia or attention deficit hyperactivity disorder.

Human oscillatory activity associated to reward processing in a gambling task.

Previous event-related brain potential (ERP) studies have identified a medial frontal negativity (MFN) in response to negative feedback or monetary losses. In contrast, no EEG correlates have been identified related to the processing of monetary gains or positive feedback. This result is puzzling considering the large number of brain regions involved in the processing of rewards. In the present study we used a gambling task to investigate this issue with trial-by-trial wavelet-based time-frequency analysis of the electroencephalographic signal recorded non-invasively in healthy humans. Using this analysis a mediofrontal oscillatory component in the beta range was identified which was associated to monetary gains. In addition, standard time-domain ERP analysis showed an MFN for losses that was associated with an increase in theta power in the time-frequency analysis. We propose that the reward-related beta oscillatory activity signifies the functional coupling of distributed brain regions involved in reward processing.

Beneficial effects of word final stress in segmenting a new language: evidence from ERPs.

BACKGROUND: How do listeners manage to recognize words in an unfamiliar language? The physical continuity of the signal, in which real silent pauses between words are lacking, makes it a difficult task. However, there are multiple cues that can be exploited to localize word boundaries and to segment the acoustic signal. In the present study, word-stress was manipulated with statistical information and placed in different syllables within trisyllabic nonsense words to explore the result of the combination of the cues in an online word segmentation task. RESULTS: The behavioral results showed that words were segmented better when stress was placed on the final syllables than when it was placed on the middle or first syllable. The electrophysiological results showed an increase in the amplitude of the P2 component, which seemed to be sensitive to word-stress and its location within words. CONCLUSION: The results demonstrated that listeners can integrate specific prosodic and distributional cues when segmenting speech. An ERP component related to word-stress cues was identified: stressed syllables elicited larger amplitudes in the P2 component than unstressed ones.

Hand Position and Response Assignment Modulate the Activation of the Valence-Space Conceptual Metaphor.

Conceptual metaphor is ubiquitous in language and thought, as we usually reason and talk about abstract concepts in terms of more concrete ones via metaphorical mappings that are hypothesized to arise from our embodied experience. One pervasive example is the conceptual projection of valence onto space, which flexibly recruits the vertical and lateral spatial frames to gain structure (e.g., good is up-bad is down and good is right-bad is left). In the current study, we used a valence judgment task to explore the role that exogenous bodily cues (namely response hand positions) play in the allocation of spatial attention and the modulation of conceptual congruency effects. Experiment 1 showed that congruency effects along the vertical axis are weakened when task conditions (i.e., the use of vertical visual cues, on the one hand, and the horizontal alignment of responses, on the other) draw attention to both the vertical and lateral axes making them simultaneously salient. Experiment 2 evidenced that the vertical alignment of participants' hands while responding to the task-regardless of the location of their dominant hand-facilitates the judgment of positive and negative-valence words, as long as participants respond in a metaphor-congruent manner (i.e., up responses are good and down responses are bad). Overall, these results support the claim that source domain representations are dynamically activated in response to the context and that bodily states are an integral part of that context.

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.

Neurophysiological evidence for the interplay of speech segmentation and word-referent mapping during novel word learning.

Learning a new language requires the identification of word units from continuous speech (the speech segmentation problem) and mapping them onto conceptual representation (the word to world mapping problem). Recent behavioral studies have revealed that the statistical properties found within and across modalities can serve as cues for both processes. However, segmentation and mapping have been largely studied separately, and thus it remains unclear whether both processes can be accomplished at the same time and if they share common neurophysiological features. To address this question, we recorded EEG of 20 adult participants during both an audio alone speech segmentation task and an audiovisual word-to-picture association task. The participants were tested for both the implicit detection of online mismatches (structural auditory and visual semantic violations) as well as for the explicit recognition of words and word-to-picture associations. The ERP results from the learning phase revealed a delayed learning-related fronto-central negativity (FN400) in the audiovisual condition compared to the audio alone condition. Interestingly, while online structural auditory violations elicited clear MMN/N200 components in the audio alone condition, visual-semantic violations induced meaning-related N400 modulations in the audiovisual condition. The present results support the idea that speech segmentation and meaning mapping can take place in parallel and act in synergy to enhance novel word learning.

The effects of stress and statistical cues on continuous speech segmentation: an event-related brain potential study.

The study of the processes involved in speech segmentation has gained special relevance in recent years by trying to establish what type of information listeners use to segment the speech signal into words. An event-related brain potential experiment was conducted in order to understand how two of these cues (statistical and stress cues) interact. The experiment consisted of the presentation of artificial speech streams in which words were marked either by statistical cues alone, or by a combination of statistical and stress cues. As a baseline, comparison streams were also created with the same syllables but organized in random order. Results showed an N400 component that marks the on-line segmentation of speech into words, and an increased positivity (P2 component) for languages that include both types of cues. Possible implications of these results for the process of speech segmentation are discussed.

Headstart for speech segmentation: a neural signature for the anchor word effect.

Learning a new language is an incremental process that builds upon previously acquired information. To shed light on the mechanisms of this incremental process, we studied the on-line neurophysiological correlates of the so-called anchor word effect where newly learned words facilitate segmentation of novel words from continuous speech. Higher segmentation performance was observed for speech streams embedded with newly learned anchor words. The anchor words elicited an enhanced Stimulus-preceding negativity (SPN) component considered to be an index of expectation for incoming relevant information. Moreover, we confirmed a previously reported N400 amplitude increase for the to-be-segmented novel words, indicating a bottom-up learning process whereby new memory representations for the novel words emerge. We propose that the anchor word effect indexed by SPN reflects an expectation for an incoming novel word at the offset of the anchor word, thus facilitating the segmentation process.